Pool & hot tub
calculators.
Free, instant results. Enter your numbers — get exact amounts. No signup, no ads in your way.
Every calculator here does the same basic job: it turns a test reading and a water volume into an amount you can actually measure out. Guessing a dose is how water ends up over-chlorinated, cloudy, or scaled — and how you end up buying chemicals twice. If you don't know your volume yet, start with the pool volume calculator; every chemical result on this site depends on that one number being right.
The tools are grouped four ways. Water chemistry covers dosing — chlorine, pH, alkalinity, calcium hardness, CYA and salt — plus an all-in-one water balance planner that puts the adjustments in the right order, since alkalinity moves pH and doing them backwards means redoing both. Sizing covers equipment: the pump size calculator works from your turnover requirement, the filter size calculator makes sure the filter can handle whatever the pump pushes at it, and the heater size calculator works from surface area and the temperature rise you want. Cost estimates what heating, chemicals and electricity add up to over a season.
Hot tubs get their own set. A spa holds a few hundred gallons against a pool's tens of thousands and runs far hotter, so pool doses are wildly wrong at that scale — use the hot tub chemical calculator instead of scaling a pool figure down by eye. Everything runs in your browser: no signup, no account, and your readings are never sent anywhere. Results switch between US and metric units, and each calculator explains the formula behind its answer rather than just printing a number.
Chemical dosing calculators for balancing your pool water.
Water Balance (All-in-One)
Enter all readings, get a complete treatment plan with order and timing.
Chlorine Calculator
Calculate liquid chlorine, bleach, or dichlor amounts to reach your target FC.
Pool Shock Calculator
Breakpoint chlorination dosing for calcium hypochlorite, dichlor, or liquid shock.
pH Calculator
Muriatic acid or soda ash amounts to raise or lower pH to 7.2-7.6.
Alkalinity Calculator
Baking soda or muriatic acid to adjust total alkalinity to 80-120 ppm.
Calcium Hardness Calculator
Calcium chloride dosing to reach 200-400 ppm and prevent surface damage.
CYA / Stabilizer Calculator
Cyanuric acid dosing to protect chlorine from UV sunlight degradation.
Salt Pool Calculator
How many pounds/bags of salt to reach the ideal 3,200 ppm for SWG pools.
Determine your pool volume and equipment requirements.
Pool Volume Calculator
Calculate volume in gallons or liters for rectangular, round, oval, and irregular shapes.
Pool Heater Size Calculator
Find the right BTU output based on surface area, location, and desired temperature.
Pool Pump Size Calculator
Calculate correct pump GPM and HP for your pool volume and plumbing.
Pool Filter Size Calculator
Determine the right filter square footage for your pool and flow rate.
Pool Filter Sand & DE Calculator
How many pounds of sand or DE powder your filter needs, by tank size or area.
Estimate ongoing and one-time pool ownership costs.
Pool Heating Cost Calculator
Estimate monthly heating costs for gas, electric, heat pump, and solar heaters.
Pool Maintenance Cost Calculator
Monthly chemical, electricity, water, and service cost estimates.
Variable Speed Pump Payback Calculator
Annual savings, kWh saved, and payback years for a variable speed pump upgrade.
Heat Pump vs Gas Heater Calculator
Running-cost gap, upfront difference, and payback in seasons for a heat pump over gas.
Pool Cost of Ownership
Total annual cost breakdown for prospective and current pool owners.
Calculators designed for hot tub chemistry and sizing.
Hot Tub Volume Calculator
Calculate your hot tub volume for accurate chemical dosing.
Hot Tub Chemical Calculator
Bromine and chlorine dosing for smaller hot tub volumes and higher temperatures.
Hot Tub Heating Cost Calculator
Estimate monthly electricity costs to keep your hot tub at temperature.
Use our all-in-one Water Balance tool — enter all your test readings and get a complete treatment plan.