How much ice do you need for an ice bath? The 2026 UK numbers
Around 5.4 kg of ice per 100 litres takes summer tap water from 18°C down to 13°C. This guide gives you the formula, a season-by-season table, and the point at which ice stops making financial sense.
See the Plunge PROLast updated: September 2026
You need roughly 5.4 kg of ice per 100 litres of water to drop from 18°C to 13°C, or about 7.7 kg per 100 litres to reach 11°C. Add 20 to 30 per cent on top of that for heat leaking in from the air, the walls of the tub and the body that gets in afterwards. For a 300 litre fill in a British summer, that means roughly 20 kg of ice to hit 13°C.
Most ice bath advice online gives you a vague ratio and leaves it there. The honest answer is that the number depends on three things you can actually measure: how much water is in the tub, how warm that water starts, and how cold you need it. Get those three and the arithmetic is fixed. Everything else is insulation and logistics.
What is the formula for how much ice an ice bath needs?
Ice cools water in two stages: it absorbs 334 kJ per kilogram as it melts, then the resulting meltwater absorbs more heat as it warms to the final temperature. Combining both gives a single equation. Water's specific heat is 4.186 kJ per kilogram per °C, and one litre of water weighs one kilogram.
The equation: ice (kg) = litres × 4.186 × (start temp − target temp) ÷ (334 + 4.186 × target temp)
Worked example, 300 litres from 18°C to 13°C: 300 × 4.186 × 5 = 6279 kJ to remove. Each kilogram of ice absorbs 334 + 54.4 = 388.4 kJ. So 6279 ÷ 388.4 = 16.2 kg in theory, or roughly 20 kg once you allow 25 per cent for real-world heat gain.
Why the rules of thumb online disagree with each other
Published ratios range from 1 kg of ice per 10 litres to 1 kg per 3 litres. They are not contradictory, they are answering different questions. A 1:10 ratio delivers roughly a 4°C drop. A 1:3 ratio delivers closer to a 12°C drop. Neither is wrong, but neither tells you what you need unless you know your starting temperature.
How much ice per 100 litres, by starting temperature?
This table gives the theoretical ice requirement per 100 litres of water. Multiply by your fill volume, then add 20 to 30 per cent for practical losses. Figures are rounded to one decimal place and assume ice at 0°C.
| Water start temp | To 13°C | To 11°C |
|---|---|---|
| 20°C (hot spell, tub left outdoors) | 7.5 kg | 9.9 kg |
| 18°C (typical UK summer mains) | 5.4 kg | 7.7 kg |
| 15°C (spring or autumn mains) | 2.2 kg | 4.4 kg |
| 12°C (typical UK winter mains) | None needed | 1.1 kg |
The pattern is the point. Between roughly November and March, UK mains water often arrives cold enough that an 11°C to 15°C session needs almost no ice at all. Reported UK mains temperatures range from around 10°C in winter to around 20°C in summer. Your ice bill is a summer problem, not a year-round one.
How cold does the water actually need to be?
Colder is not automatically better, and chasing 5°C multiplies your ice requirement for no clear gain on soreness. A 2025 network meta-analysis in Frontiers in Physiology found that 10 to 15 minutes at 11°C to 15°C was the dose that best reduced delayed onset muscle soreness, with 10 to 15 minutes at 5°C to 10°C performing better on biochemical and neuromuscular markers.
That matters for your shopping list. If 11°C to 15°C is your working band, the table above is the whole job. If a coach insists on single digits, expect to roughly double the ice for the same volume. We cover the dose question in full in our guide to ice bath temperature and duration.
Buy a thermometer before you buy ice: a £10 digital probe removes all the guesswork here. Measure the water as it comes out of the tap, run the equation, and you stop over-ordering by habit.
Timing matters as much as temperature. If cold is going in near a strength session, read the evidence-based protocol for footballers first.
Does tub insulation change how much ice you need?
Yes, and it is the single biggest lever most buyers ignore. Ice quantity is set by physics, but how long that cold lasts is set by the tub. A poorly insulated tub with a fabric cover loses temperature to the air continuously, so you pay for ice twice: once to reach the target, again to hold it for a second or third user.
This is why build matters more than capacity. Plunge PRO pairs 8 cm drop-stitch walls with an 8 cm rigid inflatable lid, where the usual competitor pattern is 5 cm walls and a fabric cover. Rigid insulation on the top surface matters because that is where most of the heat arrives when the tub is sitting idle between users.
- Fill once, use several times. A tub that holds temperature lets a squad rotate through one fill rather than re-icing between groups.
- Lid on between users. An open tub in a warm changing area loses cold fast. Treat the lid as part of the protocol, not as storage.
- Site it out of direct sun. Radiant heat on a dark tub in July costs real money in ice.
- Top up rather than restart. Adding a few kilograms to bring water back into band is far cheaper than draining and re-icing.
Is bagged ice or a chiller cheaper in the UK?
Bagged ice in the UK is commonly quoted at around £0.60 to £1.00 per kilogram, which puts a 20 kg summer fill at roughly £12 to £20. Water chillers typically start from around £1,000 and cost pennies per day to run. The crossover point is frequency, not principle.
| Usage pattern | Cheaper option | Why |
|---|---|---|
| A few sessions a month, seasonal | Bagged ice | No capital outlay |
| Daily through summer, one user | Chiller | Ice spend compounds |
| Squad sessions, 2 to 3 days a week | Bulk ice or ice machine | Volume beats chiller output |
| Winter only, UK | Neither | Mains water is already in band |
One caveat worth stating plainly: a domestic chiller has a fixed cooling rate, so it struggles to pull a large volume down quickly after a squad has warmed it. For team use, bulk ice or an on-site ice machine is usually the faster route. Our ice bath buying guide covers the full kit decision.
How much ice does a squad session need?
A single 300 litre tub serving a rotating group in summer typically needs the initial charge plus a top-up. Budget the initial requirement from the table, then hold back roughly a quarter of it to bring water back into band once bodies have warmed it. Plan the sequence rather than improvising at pitchside.
- Fill and measure. Record the tap temperature. In winter, check before you order anything.
- Calculate, then add 25 per cent. Use the equation above on your actual fill volume, not the tub's rated capacity.
- Charge, stir, verify. Ice sitting on the surface does not mean the water is at temperature. Stir and re-measure before the first athlete gets in.
- Lid on between groups. Every minute open is heat gained.
- Top up on temperature, not on a timer. Measure, then add only what the reading requires.
- Log the water. Multi-user fills raise hygiene as well as temperature questions. See our water change and filtration protocol.
Screening comes before any of this. Cold water immersion is not appropriate for every athlete, and clubs should have a documented process. Our guide on cold water immersion safety and contraindications sets out the checks.
If you are specifying kit for an academy, clinic or national governing body, MyVYRO runs a partner programme with volume terms and direct support for performance staff. Get in touch through the site.
Most inflatable tubs pair 5 cm walls with a fabric cover. The Plunge PRO pairs rigid drop-stitch walls with a rigid inflatable lid, and sets up in minutes with no plumbing.
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Frequently asked questions
How many bags of ice do I need for an ice bath?
Supermarket bags are usually 2 kg. For a 300 litre fill at 18°C targeting 13°C, you need roughly 20 kg, so about 10 bags. In winter, when mains water is near 12°C, you may need one or two bags or none at all.
How long does it take ice to cool an ice bath?
Most of the cooling happens within 5 to 10 minutes of adding ice, provided you stir. Ice left floating undisturbed cools the top layer first and can read several degrees colder at the surface than at depth. Always stir and re-measure before use.
Do you need ice in an ice bath in winter?
Often not. Reported UK mains water sits around 10°C to 12°C in winter, which is already inside the 11°C to 15°C band used in most recovery protocols. Measure the tap temperature first rather than buying ice out of habit.
Is salt or cold water better than ice for cooling a plunge?
Salt lowers the freezing point, so an ice and salt mix can reach lower temperatures than ice alone. For an 11°C to 15°C target it is unnecessary, adds cost, and makes the water harsher on tub materials and skin. Plain ice is sufficient.
Can I reuse ice bath water to save on ice?
Yes, and reusing water is the main way to cut ice spend, because an already-cold fill needs far less topping up. Hygiene sets the limit rather than temperature. Follow a documented change and filtration schedule, especially for multi-user club setups.
Written by Jonny Weekes, MyVYRO. Sources: Frontiers in Physiology (2025) network meta-analysis on cold water immersion dose and exercise-induced muscle damage; published UK mains water temperature ranges; standard thermodynamic values for the enthalpy of fusion of ice and the specific heat capacity of water. We supply the Pulse PRO and Plunge PRO to clubs, gyms, clinics and performance staff across the UK. British English throughout. For general education, not medical advice.