Ice Bath Ice Calculator: How Much Ice Do You Need?

Buying ice by guesswork means either a lukewarm plunge or a tenner of wasted bags. This calculator uses the actual physics of melting ice (it absorbs a large burst of heat as it melts) to tell you how much ice in kilograms and supermarket bags you need to hit your target temperature from your current water temperature.

The maths assumes the ice starts at 0°C and the tub is insulated, so heat from the air and ground is ignored over a short fill. In a thin uninsulated tub on a warm day you'll need more, because the water keeps gaining heat while the ice works. If you plunge most days, this is the running cost that pushes people towards a chiller.