All pool and hot tub calculators
Every calculator on the site, grouped by job: volume, chlorine, water balance, hot tubs, equipment and running costs. Each one works in US or metric units and shows the working behind its answer.
Pool & spa volume
- Pool Volume CalculatorGallons or litres in a rectangle, round, oval or kidney pool, with a flat or sloped floor.
- Above-Ground Pool Gallons CalculatorGallons in a round, oval or rectangular above-ground pool from its size, wall height and how full you fill it.
- Hot Tub Gallons CalculatorEstimated gallons in a hot tub from its outside size, based on manufacturers’ published capacities — the number every spa chemical dose needs.
- Kiddie Pool Gallons CalculatorHow many gallons a round or rectangular kiddie or paddling pool holds at the depth you fill it — and how long it takes to fill.
Chlorine
- Pool Chlorine CalculatorHow much liquid chlorine, bleach, cal-hypo, dichlor or trichlor raises free chlorine to your target — plus the stabilizer, calcium or salt each one adds.
- Liquid Chlorine & Bleach CalculatorFluid ounces, cups or gallons of liquid chlorine or plain bleach to raise free chlorine by any amount, and how many jugs that is.
- Pool Shock CalculatorHow much shock — cal-hypo bags, liquid chlorine, bleach or dichlor — to superchlorinate, clear algae (SLAM level) or follow the CDC’s accident response.
- Chlorine Tablet CalculatorHow many 3-inch chlorine tablets a week your pool needs — and how much stabilizer (CYA) they add over a season.
- Chlorine & Stabilizer (FC/CYA) CalculatorThe free chlorine level your pool needs for its stabilizer (CYA) level: minimum, shock level and the public-pool limits.
- Hot Tub Chemical Calculator (Chlorine, Bleach, Bromine)How much dichlor, bleach or liquid chlorine raises a hot tub’s chlorine to target — or how much bromide booster and how many bromine tablets to start a bromine tub.
Water balance
- Pool Salt CalculatorPounds or kilograms of pool salt — and how many 40 lb bags — to bring a salt water pool up to your chlorinator’s target.
- Muriatic Acid Calculator (pH & Alkalinity Down)How much muriatic acid or dry acid to lower pH or total alkalinity, worked from your test results and pool volume.
- Pool Stabilizer (CYA) CalculatorHow much stabilizer (cyanuric acid, conditioner) raises CYA to your target — granular or liquid — and the chlorine level that CYA then needs.
- Baking Soda Calculator (Raise Alkalinity)How much baking soda (sodium bicarbonate, alkalinity up) raises total alkalinity to target — and what it does to pH.
- Soda Ash Calculator (Raise pH)How much soda ash (pH up) raises your pool’s pH to target, estimated from pH, alkalinity, stabilizer and temperature.
- Calcium Hardness CalculatorHow much calcium chloride (hardness increaser) raises calcium hardness to target, for pools and hot tubs.
- Drain & Refill Calculator (Lower CYA, Salt, Calcium)How much water to drain and refill to bring stabilizer (CYA), salt, calcium or TDS down to target — in one go or in safer partial drains.
- Saturation Index (LSI) CalculatorLangelier saturation index for pool or spa water: is it corrosive, balanced or scale-forming — and what pH would balance it.
Pumps & filters
- Pool Pump Size Calculator (GPM & Turnover)The flow your pump needs to turn the pool over in the hours you choose, checked against your pipe size and filter.
- Pool Filter Sand CalculatorHow much #20 silica sand your sand filter takes, by model: Hayward, Pentair Triton II, Sand Dollar and Intex, in pounds and 50 lb bags.
Heating & running costs
- Pool Heater Size & Heat-Up Time CalculatorWhat size pool heater you need (BTU/h or kW) and how many hours a heater takes to warm the pool.
- Pool Heating Cost CalculatorWhat a gas, propane, heat pump or electric pool heater costs per hour, per heat-up and per month.
- Pool Pump Cost CalculatorWhat your pool pump costs to run per day, month and season, and what a variable-speed pump at a lower speed would save.
- Pool Running Cost Calculator (per month)A monthly pool budget: pump electricity, heating, chemicals, top-up water and a salt cell, each line from your own prices.
- Solar Cover Size CalculatorWhat size solar cover to buy for a round, oval, rectangle or kidney pool, how much to trim, and the water and heat it saves.
Filling & water loss
- Pool Fill Time & Water Cost CalculatorHow long it takes to fill a pool with a garden hose (or several), what the water costs, and how many truckloads it would take instead.
- Pool Evaporation & Water Loss CalculatorGallons your pool loses to evaporation per day, week and year, the heat that goes with it, the top-up cost, and what a cover saves.