Know your gallons. Add the right amount.
27 calculators for pools, hot tubs and fish tanks: volume, salt, shock, chlorine, pH, heaters, pumps, costs and stocking. Each one shows the math and gives you the amount to buy.
The pool drawn here is 16 ft wide and 38 ft long (32 ft plus two 3 ft Roman ends), 3½ ft deep at the shallow end and 8 ft at the deep end. It holds 20,700 gal, the same figure the volume calculator gives for those numbers.
Pool volume & water
Every dose, heater and pump starts with gallons. Work out the volume of any pool shape, how long the hose takes to fill it, and how much water it loses in a week.
All 4 pool volume & water calculatorsPool Volume Calculator
Pick the shape, enter the size and depth, and get the water in your pool in gallons and litres, with a drawing of the pool to check it.
Pool Gallons Calculator
Pick your above-ground pool size and wall height, or enter an in-ground pool's dimensions, and see the gallons it holds.
Pool Fill Time Calculator
Enter your pool's gallons and how fast your hose runs, and see how many hours the fill takes and what the water costs.
Pool Evaporation Calculator
Enter your pool's surface area, pick your region and wind, and see the inches and gallons evaporation takes each week, with and without a cover.
Pool chemistry
Enter your test results and your gallons, and get the amount of each product to add, in the order to add it, in cups, ounces, pounds or bags.
All 11 pool chemistry calculatorsPool Chemical Calculator
Type in your test strip or kit readings and get a dosing plan in the right order, with the amount of each product and what to buy.
Pool Salt Calculator
Enter your pool size, the salt you have and the level your system wants, and get the pounds and bags to add, or how much water to replace.
Pool Shock Calculator
Pick routine shock, SLAM or algae, enter your gallons, free chlorine and CYA, and get the amount of shock, what it does to calcium and CYA, and when to stop.
Pool Chlorine Calculator
Enter your gallons, free chlorine and CYA to get the chlorine target, the amount to add in gallons, ounces or litres, and the daily top-up.
Pool Alkalinity Calculator
Enter your gallons and total alkalinity to get the baking soda or acid needed to reach your target, in parts small enough to retest between.
Heaters, pumps & filters
Size the heater for the temperature rise you want, the pump for your turnover rate, and the filter for the flow, then see what each costs to run.
All 4 heaters, pumps & filters calculatorsPool Heater Calculator
Enter your pool, the temperature you want and the hours you can wait to get heater size in Btu/h and kW, time to heat and cost for gas versus heat pump.
Pool Pump Calculator
Enter your pool volume, turnover goal and head to get the flow you need, the pump size and what a variable-speed pump saves each year.
Pool Turnover Calculator
Enter your gallons and pump flow to get turnover time and rate, or pick a target to get the GPM you need.
Pool Filter Size Calculator
Enter your pump flow or your pool and turnover goal to get the filter area you need and the sand to buy.
Pool costs
A low, typical and high price for the pool you are considering, the monthly payment on it, and what it costs to keep running.
All 3 pool costs calculatorsPool Cost Calculator
Pick the pool type, size and extras to get a low, typical and high price for your state, the monthly payment and what the first year of running it costs.
Pool Payment Calculator
Enter the pool price, your down payment, the interest rate and the term to see the monthly payment, the interest you will pay and how the balance falls each year.
Pool Resurfacing Cost Calculator
Enter the pool size and choose the finish to get a low, typical and high price for your state, with the drain, tile and coping lines you pick.
Pool Removal Cost Calculator
Choose partial fill-in, full removal or above-ground, enter the pool's size and get a low, typical and high price for your state with every line shown.
Aquarium & fish tanks
Find out how much water a tank holds and how much it weighs, how much sand or gravel to buy, how many fish it can carry and how to mix saltwater.
All 5 aquarium & fish tanks calculatorsAquarium Volume Calculator
Pick your tank shape, enter the size in inches or centimetres, and get gallons, litres, the water left after substrate and rock, and the filled weight.
Fish Tank Calculator
Choose your tank size and get gallons, litres, the weight when full, the heater and filter to buy and the load on your floor.
Aquarium Substrate Calculator
Enter the tank bottom and the depth you want, choose sand, gravel or soil, and get pounds, kilograms and the number of bags to buy.
Aquarium Stocking Calculator
Pick your tank and filter, add fish from a list of sourced species, and get a stocking level with the compatibility warnings that matter.
Salinity Calculator
Turn a hydrometer reading into ppt and mS/cm at your water temperature, then get the pounds and cups of salt mix for the water change.
Numbers you can check with a pencil.
How we calculateYour gallons, saved once
Enter your pool volume one time. Every dose, heater and cost calculator starts from it, and it never leaves your device.
The math, with your numbers
Each result prints its formula with your test values in it, so you can check it with a pencil or a phone calculator.
Ranges with a source
Targets and dose rates come from published references and product labels, and the page says which one it follows.