During the winter, many bodies of water freeze over. These include ponds, lakes, and even some rivers. Solid ice can be tempting to cross over for a variety of reasons. Despite the temptation, walking on ice can be dangerous.
Most people do not know how much weight ice can hold, which might result in a fatal accident. Ice must be at least three inches thick to hold the weight of a human.
In this article, I will explain the equation for how much weight a given piece of ice can hold, the required thickness for some common situations, and finally how to calculate ice thickness.
How Much Weight Can Ice Hold?
Ice has varying strengths based on appearance. Let us talk about them in order from strongest to weakest.
Clear ice (a.k.a. black ice) is the strongest and ideal for holding weight. The amount of weight that clear ice can hold is equal to the square of the thickness in inches (P=Ah^2).
This ice is cloudy or opaque looking because it contains air pockets. These air pockets lessen the ice’s strength, making it unpredictable. There is no reliable equation for predicting the load-bearing ability of white ice, but you can estimate its strength as being 15% less than Black Ice. It is safest to avoid this kind of ice.
This ice is called rotten because it has begun to melt. The early stages of melting ice make it appear grey or black. At this stage, it is about 50% weaker than Black Ice. As it melts further, it gets a mushy appearance. This ice is the most dangerous.
Using Gold’s Formula
The most widely used way to determine the weight ice can hold is Gold’s Formula (P= Ah^2). Here, P is the weight in pounds, h is the thickness in inches, and A is the constant psi (determined by ice quality).
A=50 when ice is black/clear. If it is White, then A=40. In the case of gray ice, you could use A=25. I give an example of how to use this formula below.
Grace is going over a lake with her snowmobile. Her, the vehicle, and the equipment weigh about 700 lbs. The equation is then 700 = 50(h^2) for average conditions. When we solve that we get h=3.74.
This indicates that 3.74 is barely enough to hold Grace and her equipment if the ice is clear and in average condition. Your estimates should always allow some wiggle room, so Grace should not go over the ice unless it is more than four inches thick.
Safe Ice Thickness to Walk on
These measurements assume black/clear ice.
An average-sized person (~200 lbs.) can walk on ice that is 3 inches thick.
When Ice fishing, you will be stationary for long periods. A stationary load requires thicker ice than a mobile one. For safety, it is best to set up an ice fishing location where the ice is six inches thick instead of three.
When skating in a group, you should aim for about six inches of ice. However, if you are skating alone, you can reduce this to three inches. Ice skating does not require as thick of ice as walking because you will be moving smoothly at speed, not slowly with the jolting impact of placing your feet on the ice.
Safe Ice Thickness to Drive on
Driving on the ice must be done in some cases. These measurements assume an average weight. You should always know the weight of your equipment. Additionally, always drive on ice slowly with your seatbelt undone and the car door open.
A small vehicle (~1200 lbs.) such as an ATV or snowmobile can be driven on six inches of ice.
Standard vehicles include compact cars, medium-sized cars, and pickup trucks. These values assume a full tank of gas and the maximum number of passengers.
A compact vehicle requires at least eight inches of ice to hold its’ average weight of 3200 lbs.
A medium-sized car requires nine inches of ice to hold an average weight of 4000 lbs. This category includes Jeeps, Sedans, and other similar-sized vehicles.
A pickup truck requires ten to twelve inches depending on size. About ten inches will accommodate a small pickup truck (5000 lbs.). Twelve inches is suggested for a full-size pickup (7000 lbs.).
When parking a vehicle, you will need greater thickness than when driving because the load is stationary. Additionally, you must move the vehicle every couple of hours and not park close to another vehicle.
This is to prevent the ice from sinking. As a tip, you can make a hole next to the car. When water starts to come up through the hole, it is time to move the car.
Parking small vehicles require 10-12 inches of ice.
A standard vehicle should not be parked on ice thinner than 13-16 inches.
A pickup truck needs 18-22 inches of ice for safe parking.
Measuring Ice Thickness
To decide if ice is safe for your purposes, you will need to measure its’ thickness.
Cordless Drill Auger
This is a portable, low-labor way to measure ice thicknesses greater than four inches. The cordless auger is battery-powered, and the drill section has markings for each inch.
Simply turn the auger on and guide it straight down into the ice until you break through. Then, locate the corresponding mark to determine thickness. You can always double-check this value with a measuring tape.
Ice Chisel or Axe
This method is low-tech and lightweight for those that need to test ice thicker than four inches. You can easily keep a chisel or axe and a measuring tape in the back of your car.
To measure thickness this way, you will need to hit the ice to create a hole, and then use the tape measure to determine the thickness of the ice.
Ice Testing Pole or Nordic Skating Pole
These poles are weighted and have a sharp tip. This is designed to break ice under a certain thickness. Some models (usually called ice testing poles) will break ice less than 3 to 4 inches, which is extremely useful for determining if ice is safe to walk on.
Nordic Skating Poles are designed to break the ice that is 2.5 inches or less, making it a good choice for skating or skiing. To use one of these poles, simply hold the sharp tip slightly above the ice, and then give it a good jab downward. If the ice does not break, it is safe.
Although not widely available or cost-effective currently, future technology deserves an honorable mention. Portable sonar devices have been developed to measure ice thickness. These may become standard soon depending on price and market interest.
When traversing ice, always make sure to bring measuring equipment with you. Testing Poles, Ice Drills, or an Axe are all great options.
Walking on ice requires at least four inches, while other activities may take more. A mobile load (such as a moving vehicle) does not require the same thickness as a standing load (a parked car).