How much ice for an ice bath? About 50 lb
How much ice for an ice bath? About 50 lb cools 100 gallons from 60°F to 50°F. A table for any tap temperature, the sum behind it, and ways to use less ice.
For checking the water
All our tub picksThe short answer
About 50 lb
That cools 100 gallons of 60°F tap water to 50°F. Warmer tap water or a colder target takes more. The rule of thumb is half a pound of ice per 10 gallons for every degree you want to drop.
For checking the water
All our tub picksHow much ice for an ice bath depends on three numbers
The ice you need comes down to how many gallons are in the tub, how warm the water is when it comes out of the tap, and how cold you want it. Most advice online skips the second one, which is why you see answers from 20 lb to 100 lb for the same tub. Both can be right. A tap that runs at 55°F in January and 72°F in August needs very different amounts of ice.
- ½ lb Ice per 10 gallons, per degree
- 8.34 lb Weight of a gallon of water
- 144 BTU Heat a pound of ice absorbs as it melts
Our maths. The half-pound rule holds for targets between 45 and 55°F.
Ice needed for 100 gallons
Find your tap temperature on the left and your target along the top. For a 50-gallon tub, halve the figure.
| Tap water | To reach 55°F | To reach 50°F | To reach 45°F |
|---|---|---|---|
| 75°F | 100 lb | 129 lb | 159 lb |
| 70°F | 75 lb | 103 lb | 133 lb |
| 65°F | 50 lb | 77 lb | 106 lb |
| 60°F | 25 lb | 51 lb | 80 lb |
| 55°F | None | 26 lb | 53 lb |
If you are unsure what to aim for, 50 to 59°F is the range the medical sources recommend. Our guide to cold plunge temperature covers it.
Work it out for your own tub
- Measure your tap water. Run the cold tap for a minute and hold a thermometer in the stream.
- Find the gallons you fill. Use the maker’s stated capacity, less a little for the water you displace when you get in.
- Work out the heat to remove. Gallons × 8.34 × the degrees you want to drop. The answer is in BTU.
- Divide by what a pound of ice absorbs. That is 144, plus your target temperature, minus 32.
Take 80 gallons of 65°F water and a target of 50°F. The heat to remove is 80 × 8.34 × 15, which is 10,008 BTU. Each pound of ice absorbs 144 + 50 − 32, which is 162 BTU. Divide one by the other and you get 62 lb.
The second number matters more than it looks. Ice does two jobs. It absorbs 144 BTU per pound just turning to water, then the meltwater, which starts at 32°F, takes up another BTU per pound for each degree it warms to match the tub.
How much ice for an Ice Barrel
Ice Barrel lists the Ice Barrel 500 at 94 gallons and the Ice Barrel 300 at 77 gallons.
| Tap water | Ice Barrel 500 to 50°F | Ice Barrel 300 to 50°F |
|---|---|---|
| 70°F | 97 lb | 79 lb |
| 65°F | 73 lb | 59 lb |
| 60°F | 48 lb | 39 lb |
You won’t fill either barrel to the brim, because the water rises when you climb in. Fewer gallons means less ice, so these figures sit on the high side for the water and the low side for everything else that warms it.
Why a real session needs more
The tables assume a sealed, perfect tub. Yours isn’t one.
Warm air heats the surface the whole time the water sits there. The tub walls are at air temperature when you fill it. Then you get in, at body temperature, and warm the water yourself. On a hot afternoon in direct sun, a thin-walled tub can use up a large share of the ice before you are in it.
None of this can be put in one table, because it depends on your tub and your weather. Add a margin, and measure the water before you get in. A thermometer is cheaper than a bag of ice.
How to keep a portable ice bath cold
A portable ice bath has thin walls and little insulation, so it gains heat faster than a barrel or a hard tub. These cut the ice you buy.
- Put the lid on whenever you are not in the water, including the wait while the ice melts.
- Keep it in the shade. Direct sun on the water and the walls works against you all day.
- Fill it last. Add water and ice shortly before the session, not hours ahead.
- Use big pieces to hold, small pieces to cool. Cubes melt fast and bring the temperature down quickly. Blocks and frozen jugs melt slowly and hold it there.
- Freeze your own. A gallon jug of water, frozen, is 8.34 lb of ice you can use again tomorrow. Six of them replace a 50 lb ice run. Leave an inch of space in each jug, because water expands as it freezes.
- Keep the water. If the tub is clean and covered, yesterday’s water is colder than the tap, so the next session starts closer to the target.
Chiller vs ice: what the ice adds up to
One session’s ice is easy to shrug off. A year’s worth is not. At 51 lb a session:
| Sessions a week | Ice in a year | In 10 lb bags |
|---|---|---|
| 1 | 2,652 lb | 265 |
| 3 | 7,956 lb | 796 |
| 5 | 13,260 lb | 1,326 |
If a 10 lb bag costs you $3, three sessions a week comes to about $2,400 a year. That figure is why regular plungers buy a chiller, and why occasional ones shouldn’t. The full sums, with electricity, are in what a cold plunge costs. The same choice from the chiller’s side is in chiller or ice.
Stay on ice if
You plunge once or twice a week, your tap water is cool, or you are still finding out whether the habit sticks.
Look at a chiller if
You plunge most days, your tap runs warm for half the year, or you are tired of driving to buy ice. Our guide to chiller sizing covers which one.
An ice bath and a chilled cold plunge are the same practice with a different way of getting cold. We set the two side by side in cold plunge vs ice bath.
Common questions
How many bags of ice do I need for an ice bath?
For 100 gallons of 60°F tap water and a target of 50°F, five 10 lb bags or three 20 lb bags. Add a bag if the tub sits in the sun or your tap runs warmer.
How much ice do I need for a bathtub?
Work from the water you put in, not the tub’s size. Cooling 40 gallons by 10 degrees takes about 21 lb of ice. The half-pound rule covers any amount: half a pound per 10 gallons, per degree.
Should I wait for the ice to melt before getting in?
Wait until a stirred thermometer shows your target. Ice that has not melted has not finished cooling the water yet, so getting in early means a warmer bath than you paid for.
Can I use frozen water bottles in place of ice?
Yes. A frozen bottle cools the water by the same sum as loose ice of the same weight, and you can refreeze it. It works more slowly, because the plastic and the smaller surface slow the melt.
How do I work out the ice for a different tub?
Multiply the gallons by 8.34 and by the degrees you want to drop, then divide by 162 for a 50°F target. The result is in pounds. How we handle figures like these is on how we review.