Hot Tub Calculator
Calculate Hot Tub Volume & Costs
Calculate volume, chemicals, and heating costs for your hot tub
Formula
Gallons = (L x W x D in inches) / 231 x 0.8 | Heating BTU = Gallons x 8.34 x Temp Rise
Frequently Asked Questions
How many gallons is my hot tub?
Multiply length x width x depth in inches, divide by 231 to get gallons, then multiply by 0.8 for the actual fill volume (hot tubs are not perfect rectangles). Most 4-person hot tubs hold 250-350 gallons.
How much does it cost to heat a hot tub?
Initial heating costs $3-$8 depending on size and electricity rate. Monthly operating costs are typically $20-$50 for a well-insulated hot tub. Poorly insulated tubs can cost $75-$150 per month.
What chemicals do I need for a hot tub?
Essential hot tub chemicals include chlorine or bromine sanitizer, pH increaser/decreaser, alkalinity increaser, and test strips. Maintain chlorine at 1-3 ppm, pH at 7.2-7.6, and alkalinity at 80-120 ppm.
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