How much water does your cold plunge hold?
Knowing your plunge's water volume is critical for: chiller sizing, chemical dosing, ice calculation, and weight estimation. Use this calculator to determine the exact volume of your plunge.
Interactive volume calculator
Cold Plunge Volume Calculator
Enter your values and click Calculate.
Common plunge volumes
| Vessel | Capacity | Water weight | Total weight (with person) |
|---|---|---|---|
| Rubbermaid 50-gal stock tank (filled to 4" below rim) | ~42 gal | 350 lbs | 550 lbs |
| Rubbermaid 100-gal stock tank (filled to 4" below rim) | ~85 gal | 709 lbs | 909 lbs |
| The Cold Pod 85-gal (filled) | ~75 gal | 625 lbs | 825 lbs |
| Chest freezer conversion (5-7 cu ft) | 30-60 gal | 250-500 lbs | 450-700 lbs |
| Standard bathtub (filled) | 35-50 gal | 292-417 lbs | 492-617 lbs |
Body displacement guide
Your body displaces water when you enter the plunge. The amount depends on body size and submersion depth:
| Body type | Submersion depth | Displacement |
|---|---|---|
| Small adult (120 lbs) | Waist-deep | 8-10 gal |
| Small adult (120 lbs) | Chest-deep | 12-14 gal |
| Medium adult (170 lbs) | Waist-deep | 10-13 gal |
| Medium adult (170 lbs) | Chest-deep | 15-18 gal |
| Large adult (220 lbs) | Waist-deep | 13-16 gal |
| Large adult (220 lbs) | Chest-deep | 18-22 gal |
Why volume matters
1. Chiller sizing
Chiller HP scales with water volume. Use our chiller sizing calculator with the calculated volume.
2. Chemical dosing
Chlorine, algaecide, and other chemicals are dosed per gallon. Adding too much chlorine to a small tub is dangerous; too little to a large tub is ineffective.
3. Ice calculation
Ice needed scales directly with water volume. Use our ice calculator with the calculated volume.
4. Weight estimation
Water weighs 8.34 lbs/gallon. A 50-gallon plunge weighs 417 lbs + your body weight = 600+ lbs total. Verify your floor can handle this.
5. Drain/refill planning
Knowing volume helps estimate drain time (50 gal through garden hose = ~25 minutes) and refill time.
How to measure your tub
- Measure interior dimensions (not exterior — wall thickness varies)
- Measure water depth you'll use (typically 4" below rim to prevent overflow)
- Subtract body displacement based on your size and submersion depth
- For irregular shapes, measure in sections and add volumes
For chest freezer conversions
Chest freezer interior volume is measured in cubic feet. To convert to gallons:
Gallons = cubic feet × 7.48
Examples:
- 5 cu ft freezer = 37 gallons (when filled to 4" below rim, ~30 gal usable)
- 7 cu ft freezer = 52 gallons (when filled to 4" below rim, ~42 gal usable)
- 10 cu ft freezer = 75 gallons (when filled to 4" below rim, ~60 gal usable)
Recommended vessels by volume
- Rubbermaid 50-gal — Most popular, 42 gal usable
- The Cold Pod 85-gal — Insulated, 75 gal usable
- AS ColdPlunge XL — Inflatable, 100+ gal
- Pond liner — For chest freezer conversions
The most accurate way to measure your tub's volume: fill it to your target depth with a hose that has a flow meter (or time how long it takes to fill a known-volume container, then time filling the tub). This accounts for irregular shapes and rounded corners that math-based calculations miss.
For chiller sizing based on volume, see our chiller calculator. For ice needed, see our ice calculator. For electricity costs, see our electricity calculator.