How much ice for an ice bath? UK calculator
How many kilos and bags of ice your ice bath needs to reach a target temperature, what that costs a month in the UK, and when a chiller pays for itself.
About 21 kg of ice (11 bags of 2 kg) per plunge
About £22.00 a session and £381 a month at 4 plunges a week. Assumes shop ice at about -10C and 30% extra for heat gained while it melts. Ice added to warm water melts in minutes: plunge soon after.
Ice needed by tub size and tap temperature
Kilograms of shop-bought ice per plunge for an uninsulated tub (inflatable, stock tank or bath), including 30% for heat gained while it melts. UK mains water runs from about 8-10C in winter to 15-18C in late summer.
| Starting and target temperature | 150 litres | 250 litres | 350 litres | 450 litres |
|---|---|---|---|---|
| Winter tap water 10C to 5C | 11 kg | 18 kg | 25 kg | 33 kg |
| Spring tap water 13C to 6C | 15 kg | 25 kg | 35 kg | 45 kg |
| Summer tap water 17C to 10C | 14 kg | 24 kg | 34 kg | 43 kg |
| Summer tap water 17C to 5C | 26 kg | 43 kg | 61 kg | 78 kg |
Ice or a chiller?
Take a 250 litre tub, tap water at 15C, a target of 8C and 4 plunges a week. That is about 25 kg of ice (13 bags of 2 kg) a session, roughly £450 a month at £2 a bag. A chiller holding the same tub at 8C under a lid uses about 1.4 kWh a day even in summer, around £11 a month at 25p per kWh. The cheapest chiller in our catalogue, The Pod Company Pod Chiller at £499, would pay for itself in about 2 months against ice.
Ice still wins for occasional use: one or two plunges a week, summer only, or while you decide whether the habit sticks. A chiller wins on convenience from about three plunges a week, and it keeps the water filtered. Size one with the chiller sizing calculator, check the electricity with the running cost calculator, and read tub plus chiller versus all-in-one before you buy.
Thinking of a home ice maker instead? The countertop machines sold in the UK make 12 to 15 kg a day, which is one plunge in a small tub but three or four days of output for a full-size one. The accessories guide has the numbers.
How the calculation works
Cooling water by one degree takes 4.186 kJ per litre. Each kilo of shop ice at about -10C absorbs around 21 kJ warming to 0C, 334 kJ melting, and a little more warming to your target. Ice needed is the heat to remove divided by what each kilo absorbs, plus an allowance for heat entering the tub while the ice melts (10% for an insulated tub with a lid, 30% without). Melted ice also adds water, so a full tub may need a little drained first.
Frequently asked questions
How much ice do I need for an ice bath?
For a typical 250 litre tub filled from a UK tap at about 15C, getting to 8C takes roughly 25 kg of ice, around 13 bags of 2 kg. Colder targets and warmer tap water need a lot more: 250 litres from 17C to 5C needs about 43 kg.
Is ice or a chiller cheaper?
At 4 plunges a week the ice in our example costs about £450 a month against roughly £11 of electricity for a chiller holding the same tub at 8C, so the cheapest chiller in our catalogue (The Pod Company Pod Chiller, £499) pays for itself in about 2 months. Ice is cheaper if you plunge once or twice a week or only in summer.
How long does ice take to cool the water?
Bagged ice melts within 10 to 20 minutes in water at 12-17C, and the water starts warming again as soon as it has melted. Add the ice just before you get in, stir it, and check the temperature with a floating thermometer.