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How much ice for an ice bath?
Enter your water volume and temperatures. Get pounds or kilograms, a bag count, and the extra water from melting ice.
A calculation you can check.
53 gallons, 77°F → 50°F.
With ice starting at −0.4°F, the ideal estimate is 67.2 lb (30.5 kg): seven 10 lb bags to buy. The calculated mass adds 8.0 gallons of meltwater. Adding every full bag adds more water and may overshoot the target.
| Water in tub | Calculated ice | 10 lb bags | Meltwater |
|---|---|---|---|
| 25 US gal | 31.7 lb / 14.4 kg | 4 | +3.8 US gal |
| 53 US gal | 67.2 lb / 30.5 kg | 7 | +8.0 US gal |
| 100 US gal | 126.7 lb / 57.5 kg | 13 | +15.2 US gal |
Ideal estimates, not measured tub performance. Meltwater uses calculated mass, not rounded bags. A warm tub, sunlight and air can increase ice needs.
How the ice calculation works
Heat lost by the water warms the ice to 0°C, melts it, then warms the meltwater to your target. Water is approximated as 1 kg per liter.
Ice kg = water liters × 4.186 × (start °C − target °C) ÷ [2.09 × (−ice °C) + 334 + 4.186 × target °C]
Constants: water heat capacity 4.186 and ice heat capacity 2.09 kJ/kg·°C; heat of fusion 334 kJ/kg. Sources: OpenStax on heat capacity and melting and latent heat.
The model excludes heat from your body, container, air and sun. It does not calculate cooling time, cold retention or a suitable exposure temperature. It does not apply directly to sealed ice packs or frozen bottles.