Ice Bath Calculator: How Much Ice Do I Need?
Enter how much water is in your tub, how warm it is and the temperature you want. You get the minimum amount of ice to get there, worked out from the physics of melting ice.
Result
The amount of ice that would cool your water to the target if no heat came in from outside.
Real tubs warm up from the air, the sun, the tub walls and you, so buy a bag or two more than this and check the water with a thermometer. Beginners should stay between 50 and 59°F (10 to 15°C), and never go below 40°F (4°C).
How the ice calculation works
Ice cools water by absorbing heat as it warms up and melts. Melting one kilogram of ice takes 334 kJ, which is why a little ice goes a long way. The calculator works out how much heat has to come out of your water to drop it from the starting temperature to your target, then divides that by the heat each kilogram of ice can absorb.
- Heat to remove = water mass × 4.186 kJ/kg·°C × (start − target)
- Heat absorbed per kg of ice = warming the ice to 0°C (2.09 kJ/kg·°C) + melting it (334 kJ/kg) + warming the meltwater to the target (4.186 kJ/kg·°C)
One litre of water is counted as one kilogram, and one US gallon as 3.785 litres. The answer is a floor, not an exact shopping list: heat keeps leaking into the tub while you fill it and while you sit in it.
Worked example
An 80-gallon tub of 60°F tap water, cooled to 50°F with store-bought ice, needs about 41 lb of ice at minimum, so around five 10 lb bags. Summer tap water is warmer, so the same tub needs more ice in July than in January.
Ice or a chiller?
If you plunge a few times a week, the ice adds up. A cold plunge chiller holds the water at a set temperature with no ice at all. Read our cold plunge temperature guide to pick a target.
FAQ
How much ice do I need for an ice bath?
It depends on how much water you use, how warm it starts and how cold you want it. For example, 80 gallons of 60°F water needs about 41 lb of store-bought ice to reach 50°F, before allowing for heat from the room. Enter your own numbers above.
How much ice for a bathtub ice bath?
A typical bathtub holds far less water than a cold plunge tub. Enter the amount of water you fill to and your tap water temperature, and the calculator gives the minimum ice.
Can ice cool the water below 32°F?
No. Melting ice holds water at about 32°F (0°C) at best, and you should not plunge below 40°F (4°C) anyway.
Constants: specific heat of water 4.186 kJ/kg·°C, specific heat of ice 2.09 kJ/kg·°C, latent heat of fusion of ice 334 kJ/kg. Temperature guidance: Cleveland Clinic, What to know about cold plunges.