When is ice safe? There is no for-certain absolute answer. Really, ice should never be considered safe. Though there are some ice thickness safety guidelines to follow (listed below).

Ice Safety

You can’t judge the strength of ice just by its appearance, age, thickness, temperature, or whether or not the ice is covered with snow.

Ice strength is based on ALL these factors — plus the depth of water under the ice, size of the water body, water chemistry and currents, the distribution of the load on the ice, and local climatic conditions.

New Ice vs Old Ice

New ice is usually stronger than old ice. Four inches of clear, newly‑formed ice may be a safe ice thickness support one person on foot, while a foot or more of old, partially‑thawed ice may not.

Ice Thickness Uniformity

Ice seldom freezes uniformly. It may be a foot thick in one location and only an inch or two just a few feet away.

Ice Over Flowing Water

Ice formed over flowing water and currents is often dangerous. This is especially true near streams, bridges and culverts. Also, the ice on outside river bends is usually weaker due to the undermining effects of the faster current.

Snow Over Ice

The insulating effect of snow slows down the freezing process. The extra weight also reduces how much weight the ice sheet can support.

Ice Near Shore vs Farther Out

Ice near shore can be weaker than ice that is farther out.

Booming Ice

Booming and cracking ice isn’t necessarily dangerous. It only means that the ice is expanding and contracting as the temperature changes.

Fish Movements

Schools of fish in a given location can also adversely affect the relative safety of ice. The movement of fish can bring warm water up from the bottom of the lake. In the past, this has opened holes in the ice causing snowmobiles and cars to break through.

Safe Ice Thickness | Guidelines

For New, Clear Ice Only (and listed caveats)

2″ Ice or less – STAY OFF!

4″ Okay for Ice Fishing or activities on foot

5″ Ice Thickness for Snowmobile or ATV

8″ – 12″ Thick Ice for Car or small Pickup

12″ – 15″ Ice Thickness for Medium Truck

How To Check Ice Thickness

One way is to use a cordless drill with a Long 5/8 inch Wood Auger Bit (like this one on amzn). It won’t take long to drill through the ice to check the depth. Just use a small tape measure to check.

White Ice vs Clear Ice

White ice, sometimes called “snow ice,” is only about one-half as strong as new clear ice so the above thicknesses should be doubled.

Ice Thickness Can Vary Widely

Ice is seldom the same thickness over a single body of water. It can be two feet thick in one place and one inch thick a few yards away due to currents, springs, rotting vegetation or school of rough fish.

Vehicle Spacing On Ice

Vehicles weighing about one ton such as cars, pickups or SUVs should be parked at least 50 feet apart and moved every two hours to prevent sinking. It’s not a bad idea to make a hole next to the car. If water starts to overflow the top of the hole, the ice is sinking and it’s time to move the vehicle!

Never Go Out Alone

Use the Buddy System. Have a length of rope. If you go through the ice while you’re alone, well, that’s bad on you.

The Most Popular Ice Cleats

Crampons Ice Cleats
(view on amzn)

Some ice safety data sourced from the Minnesota Department of Natural Resources – I figured that those in MN certainly ought to have good information about this! (“Land of 10,000 Lakes”)

Continue reading: Wind Chill Frostbite Chart