Hot Tub Calculators
Volume, chemical doses and monthly running cost for acrylic, inflatable and wooden tubs.
- Hot Tub Volume CalculatorEstimate how many gallons or litres your hot tub holds, for acrylic spas with molded seats, inflatables and wooden or tiled tubs, round or square.
- Hot Tub Chemical CalculatorGet exact hot tub doses for chlorine, pH and alkalinity from your spa’s volume and test results, in ounces or grams, in the right order.
- Hot Tub Running Cost CalculatorEstimate what your hot tub costs to run each month from its size, your weather, how often you soak and your electricity price. Works with US and UK prices.
Small water, small doses
A hot tub holds a few hundred gallons, so a dose that would barely register in a pool can overshoot in a spa. Start by finding the real volume with the hot tub volume calculator. For acrylic spas, the manual’s capacity figure is the best number to use if you have it.
Hot water changes the chemistry
At 100°F and up, chlorine is used up faster and germs grow faster, which is why the CDC recommends at least 3 ppm free chlorine in hot tubs compared with 1 ppm in pools. The CDC also advises against cyanuric acid in hot tubs, so stabilized products like dichlor need regular water changes.
What it costs to keep hot
Most of a hot tub’s electricity goes on keeping it hot under the cover, and on reheating after the cover has been off. The running cost calculator estimates both from your weather and how often you soak.