Tool

Cold plunge ice calculator

Enter your tub volume and temperatures to see the ice needed for one full cool-down. The physics is simple, and the answer is a floor.

Water volumeliters300 L is about 79 gallons. Multiply gallons by 3.785 for liters.Starting water temperature°FTarget temperature°FIce price, low$/lb$0.20 per lb is the low end of the ThePricer range for 10 lb bags.Ice price, high$/lb$0.50 per lb is the high end of that range.

Heat to remove18,772 kJ

Ice needed (floor)53 kg / 116.7 lb

Ice cost$23.35 to $58.37

How it works

Melting ice absorbs about 333.55 kJ per kilogram and liquid water has a specific heat of about 4.184 kJ per kilogram per kelvin. The calculator multiplies water mass by 4.184 and by the temperature drop, then divides by the heat each kilogram of ice absorbs, which is 333.55 plus the 4.184 kJ per kelvin it takes to warm the meltwater up to your target. It is the same method I use by hand in do you need a chiller, where a 300 L tub from 68°F to 41°F comes out near 53 kg.

Why the real number is higher

The calculation assumes no heat leaks in from the air, the tub walls or your body. Treat it as a floor. The two ice prices are the low and high end of what ThePricer lists for 10 lb bags; replace them with what your store charges. If you plunge often, a chiller starts to make sense, and the electricity guide shows how to price it.