Hot Tub Volume Calculator
Your spa's gallonage is the number every chemical dose, heating cost and shock treatment depends on. Most portable hot tubs hold 250鈥?50 gallons; swim spas hold 1,500鈥?,500.
How the math works
- Round: 蟺 脳 (diameter 梅 2)虏 脳 depth 脳 7.48 梅 1,728 (cubic inches 鈫?gallons)
- Square/Rectangular: Length 脳 Width 脳 Depth 脳 7.48 梅 1,728
- Corner: 陆 脳 (L 脳 W) 脳 Depth 脳 7.48 梅 1,728
- Seats & footwell: the shell geometry isn't all water 鈥?the standard deduction is 15鈥?0% for a typical 5鈥? seat layout. That's why your 400-gallon-labeled tub may really hold ~330.
Measure to the water line, not the top rim 鈥?the difference is often 20鈥?0 gallons.
Frequently asked questions
Why does my manual say a different gallonage?
Manufacturers quote the shell's full capacity to the rim, before seats, headrests and footwell. The real working volume is typically 15鈥?0% lower 鈥?and dosing should always use the real working volume.
How many gallons is a 6-person hot tub?
Typically 320鈥?50 gallons of actual water, depending on layout. A large swim spa runs 1,500鈥?,500 gallons.
Why does volume matter so much in a hot tub?
Small water + high temperature (100鈥?04掳F) means chemistry moves fast: one tablespoon of chlorine in a 350-gallon tub can swing the reading several ppm. Dose small, retest, repeat.