How Many Gallons of Propane in a 20 lb Tank

It can be a bit confusing. That is, how many gallons of propane to expect in a standard 20 lb tank (typical barbecue grill size) when it’s “full”.

However, I’m going to make it simple for you (as simple as I can).

You will most likely get 4 gallons of propane when you bring your empty 20 lb propane tank to get it refilled.

Technically, the tank won’t be filled to it’s maximum capacity. But for safety reasons, a 20 lb propane tank should only fill to 80% of it’s maximum. If you were somehow able to fill the tank completely (unsafe) it would hold 5 gallons of propane.

Most consider a “full” 20 lb propane tank to hold 4 gallons of propane.

Note: Apparently today’s ‘exchange’ propane tanks might only be filled with 15 pounds, or about 3.5 gallons.

One quick and easy way to know how much is in the tank:

BBQ grill propane tank gauge specifically calibrated for 20-pound (5-gallon)

(view on amzn)
propane tank scale for bbq grill

Why just 80% (4 gallons)?

Temperature plays a role. When the temperature rises, the LPG (propane) gas expands. Leaving a 20% empty margin in the tank will provide a level of safety.

If a tank is overfilled and has rust at the seems or other defects, it can fail. A rupturing propane tank is is a SERIOUS THREAT TO LIFE.

The pressure inside a propane tank is affected by temperature. It can range from about 60 psi (30 degrees F) to about 200 psi (100 degrees F).

Propane Tank Overfill Protection

Legal propane tanks will have an OPD, which is an Overfill Protection Device. It acts like a float, and will close the valve when it reaches 4.0-4.2 gallons of propane.

How do I know if my propane tank has an OPD overfill protection device?

If you open the tank’s valve and propane comes right out, you do not have an OPD. They are also recognizable by the triangular hand wheel at the top of the valve itself. The hand wheel connecting to the valve stem is tamperproof and is not interchangeable with a cylinder not equipped with the overfill prevention safety mechanism.

Propane pounds per gallon

Propane weighs 4.25 pounds per gallon.
Here’s a chart:

4.25 – 1
8.50 – 2
12.75 – 3
17.00 – 4
21.25 – 5
25.50 – 6
29.75 – 7

1. Weigh your propane tank

You might use this multipurpose luggage scale:

(view on amzn)
Luggage scale up to 110 pounds

2. Subtract it’s TW Tare Weight (stamped on tank collar).
3. Read chart above to find equivalent gallons.

A standard 20 lb propane tank will typically fill with 17 pounds, or about 4 gallons.

For more details:
[ Read: How To Tell How Full (or Empty) Your Propane Tank Really Is ]


  1. My understanding is “if you take an empty 20 lb LP tank to a big box type of store to exchange for another, your new one or newer one will be only slightly more than 2/3 of a tank “, but if you take your empty LP tank to a propane supplier, you will full 4 gallons. As far as the OPD valve is concerned,the last time I took a tank in , I paid in the area of $ 25 or $30 for the new valve plus another $15 to $20 for a tank fill. The second tank that was taken in was replaced with a new tank because the older was out of date. No big deal, it worked out ok

    1. Don’t do what I did. Just a bone headed mistake. I took my new recently purchased tank and exchange for crappy used tank at Home Depot. Regerts Regerts Regerts😬😧🙄

      1. Elad K, Yep. We always take new tanks to the farm store. Costs a little more for propane but worth it. We take old, expired tanks to the swap stations.

  2. Note: I don’t do ‘exchange tanks’. All of my tanks I’ve purchased ‘new’ and I simply bring them to a local refill station when needed. This way I know the condition of my own tanks (not abused). Plus they’re all nice and white ;)

    1. I don’t exchange tanks either. Except one I found way out of date, took it in to exchange for the newest filled Blue Rhino in the cage. I will refill it myself once it’s empty, and just keep refilling as needed. A broke preppers way of obtaining a newish tank.

      1. some fill stations in the south
        dont use the purest propane.
        if you refill in the south and take it where it gets cold you will have
        trouble getting a decent flame.

        1. Dan,
          Butane has almost the same btu content as propane. One issue with butane is that it does not vaporize easily at Temps below freezing. Since you live in the South, where freezing weather rarely occurs, they can add it in with propane and it will still work well. Northern climates this will not work as the butane will not vaporize and just sit in the tank until the outside temp warms way up.

    2. I have been filling cylinders for more than 25 years, tanks have changed a lot but 20 pounds has always been what I could legally put into a BBQ tank. 47.6 / 8.34 pounds per gallon is 5.7 not 5 even therefor without an O.P.D. BBQ tanks could hold close to 25 pounds. Exchange programs put less than the 20 full pounds a BBQ tank can legally hold to cover the of painting rusty tanks and revalving outdated tanks.

  3. If I may add;

    There is an article on MSB about how to safely store Gas/Fuel/Propane, please review this article and its comments. DON’T BLOW YOURSELF UP, dead is for a very long time. (link please Ken) or do a search.

    I also do not use exchange tanks, I purchase and own my tanks, many times used and have them inspected and ALWAYS have the valves replaced at $15.oo a valve, that’s cheap insurance.
    I get them filled at a local Propane Supplier; they will NOT fill any tanks (small tanks under 100#) without an OPD valve. Also they also check the ‘manufactured date’ they offer a “re-test” for tanks and will re-stamp the tanks for continued use.

    As a side note; 100 pound or larger tanks do not require the OPD valve or date tests.

    PS; just called my supplier, to fill a 20#er its $9.00 plus tax…….
    Household tanks 250 plus is $1.80 per gallon…..

    1. In my area it’s anything over 40lb tanks. I have a 50lb and 100lb tank and the COOP will fill all my 20lb tanks at the discount bulk rate if I bring one of the larger tanks to be filled.

  4. Thanks for the article Ken.

    I do the same as you ( buying a new tank and refilling. When the tank becomes rusted to a degree, most propane refill stations will refuse to refill your tank so it is a built in safety measure to not; “paint your tank in order to make it pretty”.

    Most propane tanks I have had have lasted some 5 to 10 years prior to turning the tank in to obtain a new one.

    On pre-filled tanks: I have had bad experiences with the Blue Rhino drop off tanks when cooking at a mobile kitchen operation. Nothing like having the flame go out with a bunch of hungry diners. I have noticed others on this site having the same trouble with the pre-filled tank options.

    More reasons to take and use options that are tested and reliable prior to going on an expedition or leaving town for your off-grid cabin.

  5. We don’t use the exchange propane tanks , we own all of our 5 & 7 gallon tanks . We recently purchased a used 325 gallon above ground tank for our home . The cost of a new one was $ 1100.00 , Because we are on a budget we got the used one all checked out from Ferrellgas for $ 300.00 plus $ 165.00 delivery and setup, plus fill . This gives us 260 gallons of gas ,about a 4 year supply with our one propane range . We purchased instead of lease so we have our choice of who has the best price at fill up or top off time .

    1. Bluesman;
      Smart move on purchasing your tank, mainly because you can have other suppliers fill it with proof of purchase. Not so if you rent.
      I would have purchased but my supplier leases/rents to Seniors (over 65) for $1.oo per year, yes one dollar per year.

  6. I add that I tried to get the company to install a fill whip so I could fill my small bottles , no deal .

    1. Bluesman;
      Actually Ferrellgas will install a whip if you own the tank, talk to the Tech not the office.
      Have a neighbor that had one installed by Ferrellgas on a 250 tank, of course his the same neighbor that double powdered a 45 ACP load and tried to kill himself when he pulled the trigger :-(
      I have learned to stay away from him when he “does stuff”.

      1. NRP,
        I talked to the district manager, delivery setup man and the gas driver , nothing worked . Interesting neighbor you have , good fences make good neighbors.

  7. As per Worthington Tank chart I have. 20#/4.7 gal. 30#/7.1 gal . 40#/9.4 gal. 43.5#/10.3 gal. 60#/14.2 gal. 100#/23.6 gal. I am always on the look out for BBQ tanks being set by the road with a rusted out grill. FREE! I have quite a collection from 1 pounders up to 100 pounders plus a 250 gallon tank. Talk to your delivery guy. And see if he will fill up your smaller tanks if he has the adaptor. I get him to refill all mine in the summer. Last time it was 89¢ per gallon.

  8. Great timing on this post Ken, been wondering about something and this might be a good time to ask, along the topic so to speak.

    Has anyone looked in to converting their vehicles into propane powered? Since propane would store for 10 years it seems like a good choice for peppers, but I am by no means knowledgeable on mechanics so I’m asking the community. Thanks!

    1. I looked into converting my vehicle to propane many years ago as I worked as an operator of an LPG fractionating plant. Remember the OPEC oil embargo in the early 80’s? I decided against it then because if I remember correctly you give up about 30% of your engines horsepower potential and about 25% in mileage. Propane does have the advantage of causing a lot less carbon build up in an engine thus possibly allowing an engine to go longer between oil changes and last longer. The down side is the ethyl mercaptain they put in propane is corrosive. At normal doses this is not a problem but many times I saw double doses used when filling tank trucks at the plant loading docks. The companies were especially paranoid of lawsuits arising from home explosions and investigations showing that undetectable levels of ethyl mercaptain were used to give the gas that rotten egg smell.
      Propane will pretty much last forever. As far as I know the only limiting factor is the tank life. If you have the money to convert a vehicle to propane and just let it sit for a bug out vehicle and change or test the tank every 12 years, go for it. It would serve that purpose great. Remember to convert a pre computerized vehicle incase of an EMP or CME. It would suck to spend all that money on a BOV only to have a CME or EMP disable it permanently. As an everyday driver, not really worth the investment in my opinion.

    2. Rob,
      I’ve had several propane powered vehicles in the past. I had it installed on a new 1981 Ford F-150 PU with the 300 ci 6 cylinder engine. This was done by a fair sized propane dealership that catered to commercial businesses. They installed it for free on a lease/purchase with the caveat that I buy all my propane from them. I don’t remember the cost of the lease. This was during the oil embargo spoken of. In Texas you had to buy a “road use permit” which approximated the gasoline tax each year. I also converted a 62 VW Beetle air-cooled 4 cylinder to run off propane during this same time period. Without going into detail, it required an adjustable regulator on the tank and a demand diaphragm valve at the carburetor. I ran the VW off a 20# bottle.
      As texasprepper pointed out, you lose performance on propane. Propane has about 82% of the btu’s per gallon as gasoline, but has a very high 110 octane rating. An engine just doesn’t wear out on propane. I was approaching 400,000 miles on that Ford, still not using any oil between changes, until my son decided he could beat that red light.
      I’ve still got the parts I used on the VW with the plan to convert my 12,5KW generator if the need arises.

      1. Thanks for the info guys! It sounds like under the right circumstances the conversion might be worthwhile. ☺

  9. Being a prepper, I notice things, Dose anyone here notice that the “4 gallons” do not go as far as they use to? Canning on my 2 burner propane stove, I use to get almost 5 cycles per 4 gal, now I get only 3. Do the burners on a propane get worn out? My stove is about 15yrs old, but I’ve never had a problem that I know of with it. I turn gas off after each use, so I don’t think leaks are the answer.

    1. If you are still getting that nice pretty blue flame you are burning about as efficiently as you can. If you are seeing lots of yellow flame check your fresh air tubes. sometimes spiders or wasps set up in them tubes blocking fresh air intake for a clean burn. If they are clear and you are still getting yellow flames, chances are pretty good either your burners are bad or your gas orifice has eroded some.

  10. I also buy all my tanks new. Seems the last 20# tanks I bought were only about $20.00 new at Sams and they have a pretty accurate gauge on them. I get them filled at our local Farm and Ranch store for $10.00 each when empty. Could probably find somewhere cheaper to get them filled but the owner of the store is a friend and I very much like keeping my business local when possible, Still way cheaper than the tank exchange places.
    Another note, as I understand it those OPD devices are required on all portable tanks. By law, propane filling stations are not supposed to refill them.

    1. Should have said, “By law propane filling stations are not supposed to refill them without the OPD valve”.

  11. How timely an article. Lol
    I was just thinking, just an hour ago, where my #20 stand.
    Two back at the ‘ bin are full. Outside with a layer of tin to keep out the elements to.prevent rust on the tanks. Not completely enclosed so they can ‘breath’ if need be. Surrounded with a dirt barrier. A was given a three way trailer fridge that I need to get working. It won’t run on 120v but need to see if I runs on gas. Will be a nice addition to the ‘bin.
    Three partial tanks on the horse trailers and one on the bar-b,
    Come on spring!

  12. I have five 20# tanks, three are mine, two swappers. One being used, four reserve. Good ideas on finding spare tanks that are safe to use. Store the spares in a shed a ways from the house. Did a a 20# TANK filled full years ago, summer, sitting outside the shed, could smell it walking by for a day or two, warm weather expansion, no cigar zone for sure. 🔥🚭😨

  13. Coincidence? I don’t th…well, yeah probably. But still,

    Today I bought a 100# propane tank for my gas grill. Then, searched for a tank level guage. Then I figured those are probably calibrated for the standard 20# tanks, plus it became obvious from online reviews that a better way to go is to weigh the tank. But it’s reeeeally heavy!

    A search led me straight to this article, posted this day! I was not looking for another prepper blog, but… maybe it’s NOT a coincidence. Mayhap this is God’s favorite prepper blog and He LED me here! Bookmarked, just in case. And I’ll be back, just as soon as I put my new Chinese Walmart $88 puny grill together and test it out (if I survive). The tank and custom hose/regulator/fitting ate most of my grill budget.

      1. There’s a lot of good people here. WELCOME,
        ( watch out for Nailbanger, He’s a CLASSIC!)

    1. Welcome Scott, glad that you found us.

      Yes, pretty well impossible to weigh your big tank…
      However you could look for the condensation line when the weather conditions reveal it.

      1. Weighing a 100# tank…. Bathroom Scale with e wood block on it so ya can see the numbers….
        But better off, just have a 20#er as a spare incase the 100#er runs out… :-)

    2. 100# tank on a BBQ grill?? You Sir, sound like you might enjoy bbq’ing. 🍻 🐂 🐖 👍 . An easy way to check how much propane is left in your ” TANK” is to take a cup of warm/hot water, and pour it on the side. If it doesn’t make a frost ring at the level of the propane. You can touch the side of the tank and feel where it gets cold. That’s how much propane is left.

      1. Livin’ in the Woods;
        I have to say, I have my BBQ grill hooked to the ‘House’ Propane, 500 gallon tank….. :-) :-) Ya can never have enough BBQ resources available. AND I do Charcoal and wood BBQ, plus a very nice Smoker I just got a few weeks ago, and yes it’s electric, so if/when ohhhhh well, but for now…. tis sweet

      2. – Welcome Scott =
        Although I must say that personally, I prefer charcoal or even wood (lots of pecan and mesquite around these parts), I certainly understand the attraction of propane and can and have used it in the past. I prefer to use it to deep fry turkeys and running canners and such.

        A 100-pounder certainly sounds like a serious barbecue aficionado to me. Once it’s up and running, be sure let us know and we’ll all try to come and help you try it out. Can’t be letting barbecue go to ‘waist’ after all.

        Seriously, Ken, thank you for the information about the OPD valves. I was unaware that the larger tanks were not required to have them and had wondered about refilling my 100-pound tank when I need to use it. Currently it is full, and just put back against future need (I have several 20-pounders I rotate for use)

        I’ll confess, a couple of my tanks were other folks discards from rusted out grills, taken back to Blue rhino or others and exchanged for the newest tank in the cage. I’ve had good luck so far.

        Nailbanger, be sure to wear your snorkel while you are out and about; it sounds like you might need it.

        – Papa S.

  14. Now that old man is in the hospital recovering from his knee operation I am in charge of the orchard. We are having a frost tonight and I have to light the propane tank with the heater on top. Followed the steps but couldn’t get the propane match to light. Finally did and too much propane escaped and it appears I have singed my hair and maybe my eyebrows. I wondered what that propane smell was in the house. Learned a lesson there.
    We also measure out tanks and keep a chart as we can’t run out in case we are having a frost.

  15. I think last year we had some posts/questions about refilling the 1# disposable cylinders. I intentionally over-filled a couple of them and left them in a tote box out in the elements. They now have a somewhat hour glass shape. But never blew the seals. I also had correctly re-filled ones in the same tote. They didn’t bulge out at all. I can send pictures if Ken wants to post them.

  16. Anyone heard from Nailbanger lately? Hawaii got nailed with 2ft of rain.
    Hey, Nailbanger, YOU OKAY MY FRIEND???????

    1. SMG
      Yea im here, Maui didnt get as much rain as Oahu or Kauai, yet….
      We have been getting a lot of rain though, still more on the way supposedly, we are under a flood watch again, im pretty sure we will get rain.
      Those other islands got hammered, not really unexpected or unprecedented though, and IMHO most of it could have been avoided as far as loss of homes IF PEOPLE DIDNT BUILD IN FLOOD PLAINS AND DIDNT RELY ON GOVERNMENT TO FIX STUFF!!!
      Havent seen sunny skies in about 3 weeks other than a few hours here or there, today is supposed to be more of the same.

      1. you would think you lived in Cordova Alaska. 165 inches of rain a year and few sunny skies

        1. Old lady;
          You went from Cordova Alaska to Magdalena NM, talk about extremes. LOLOL

        2. I went from Cordova, AK to Datil, NM much better! I went from Tucson, AZ to Cordova, AK! And many more

      2. I’m relieved your OK. To hell with the dumb ones, just take care of yourself.

  17. We buy our own tanks and we have 30 pound and 100 pound tanks. The 30 pound tanks are for our RV.

    Both of these tank sizes require ‘certification’ and when it expires, you’ve either got to get the tank(s) recertified, or you buy a new tank. Reason? No one will fill them at a propane filling station.

    We were just rejected for the 30 pounders, trying to refill them. Guess we will be buying new tanks unless we decide to go w/ the 20 pounders from here on. Kinda puts a crimp on being off-grid in an RV, boondocking., esp during cold weather.

    The 100 pound tanks, though, are what we use for greenhouse heating and for our kitchen stove/oven. Not sure what the cost will be but we do need to look into that.

    Just one more regulatory headache…

  18. Can’t seem to find an answer to this one:
    Is it OK to shake a tank to get the last bit of propane out of it?
    I’m guessing it is not because it appears to increase the pressure dramatically, but what do I know?

    1. GeneL I’ve done it but that aint much of a reference. They have a internal pressure relief valve which keeps it from overpressuring and is supposed to make it safe. I don’t think you can add more pressure to a tank by shaking it.

  19. The 80% of 20lbs myth is exactly that, a myth. It is misinformation invented and spread by tank exchanges to sell you less gas for more money. They are lying to you, and I will show you how.

    Here’s the reality. Every propane tank is required by law to have it’s water capacity, or ‘WC’ stamped on it. This is the amount of water in pounds that will fit in the tank, and its 47.6 on a 20lb propane tank. Try to follow these basic conversions:
    On a cool day, water has a density of 8.345 lbs/U.S. gal. So the total full volume of a 20lb propane tank is 5.7 gallons of water (or liquid propane or anything really). You can measure this for yourself, although trying to pull the valve off a propane tank to fill it with water is a very unsafe thing to do.
    80% of 5.70 gallons is 4.56 gallons. Meaning that the full capacity of the tank, after allowing for that 80% standard, is ~4.6 US gallons of liquid. That’s the capacity, period.

    Now how much propane is that?
    The density of liquid propane varies with temperature, but it is about 4.3 lbs per gallon on a cool day (more like 4.0 or slightly lower on a hot day).
    4.3 x 4.6 = 19.78 lbs of propane

    Now looking at it the opposite way, what if you put 20lbs of propane in the tank on an extremely hot day (115 degrees F) when the liquid propane has a density of 3.8 lbs/gal?
    20 / 3.8 = 5.2 gallons.
    5.2 gallons is still significantly below the 5.7 gallon actual capacity of the tank if it were filled to 100%

    You can safely put 20lbs of propane in a 20lb tank. Although, 4.6 gallons of liquid propane will usually weigh closer to 19lbs. Some really smart people already did all this math and safety testing when they engineered and built the tank for 20lbs. This is why they are called 20lb tanks and not 15lb tanks. Anybody who says otherwise is either misinformed, or trying to cheat you.
    Read the actual markings stamped right there on the side of every tank, and educate yourself on what they mean.

    Also as a side note, all this conversion is why the capacity is measured in pounds and not gallons, and by extension why it doesn’t make any sense that it is sold by the gallon.

  20. Full = 4 gallons is completely wrong. The 80% is already figured in. A 20 lb tank holds almost 4.7 gallons even considering the 80%. You think 4 gallons is full because tank exchange companies are not filling the tank. A refill place will.

    You can work this out yourself. Check the WC (water capacity) of the tank, which is pounds of water. A 20 lb tank marked WC 47.6 divided by the weight of water (8.3 lbs per gallon) works out to 5.7 gallons total capacity. Multiply that by 80% and you get the maximum propane: 4.7 gallons.

    Now doublecheck your answer by taking the 20 lbs and dividing by the weight of propane, 4.3 lbs/gallon. The result matches, almost 4.7 gallons of propane is the actual legal capacity of a full 20 lb tank.

    I’m a former hot-air balloonist. We need to understand propane tank weight and capacity very accurately.

  21. Just some tips for you all. If you have an old tank with a non OPD valve, just exchange it at a big box store for a “full” one. They don’t care. Their supplier will test the old tank and replace the valve and put it back into circulation. True, it won’t be completely full but now you have a certified OPD tank that you can take to a hardware or propane supplier and get it “fully” filled. Then you’re not paying to buy a brand new tank nor paying to have a new valve put in. Saves you a lot of money.

  22. 20# tanks are heavy duty. The metal is about 1/8″ thick. The valves are protected by the ring so that it is rare for a tank to be so beat up that they would be unsafe. I’ve switched out many tanks with no problems. Just look at the tank. do a quick “once over” and you can tell real quickly whether it has been thrown around or not. Also, if you get them refilled at a propane supplier, the filler will check the overall condition of the tank. It’s not “rocket science”. If the tank looks OK, is not all beat up or rusted where the valve screws in, you’re probably OK. People fear a lot of things they don’t need to fear. It’s usually due to not understanding what they are dealing with. Study, learn, educate yourself, and you’ll be fine.

  23. Thank you, thank you. I have been at the mercy of refill con artists as I pull my travel trailer around the US. Now I know enough after reading all of the information here to be alert to scams to refill less and charge more.

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