Twenty-three calculators for the numbers that come up in looking after a pool: how much water it holds, how much of a chemical to add, what size pump or filter it needs, and what the whole thing costs to run. Each one shows the formula it used and the assumptions behind it, so you can check the answer rather than take it on trust.
Water & Volume
Volume, surface area, filling time and more.
Pool Chemistry
Chlorine, pH, alkalinity, CYA, salt and more.
Chlorine
How much chlorine to add to reach the level you want.
Open calculatorAlkalinity
How much baking soda to raise alkalinity — or how to bring it down.
Open calculatorBorate
How much boric acid to reach a borate level that steadies your pH.
Open calculatorCalcium Hardness
How much calcium chloride to add to protect your plaster and grout.
Open calculatorPool Chemistry
Enter every test reading at once and get the dose for each one.
Open calculatorCyanuric Acid
How much stabiliser to add, and the chlorine level it commits you to.
Open calculatorWater Health Check
Enter your test results and see what is in range, what is not, and what to do first.
Open calculatorpH
How much acid or soda ash to move your pH into range.
Open calculatorSalt
How much salt to add to reach the level your chlorinator needs.
Open calculatorPool Shock
Work out the shock dose for your pool, based on your stabiliser level.
Open calculatorEquipment
Pumps, filters, heaters and flow rates.
Filter Size
What size sand, cartridge or DE filter your flow rate calls for.
Open calculatorHeater Size
What size heater your pool needs to reach temperature in the time you want.
Open calculatorHeating Time
How long your heater will take to bring the pool up to temperature.
Open calculatorPipe Size
Check whether your plumbing can carry the flow, and see the velocity in each size.
Open calculatorPump Size
Find the flow rate your pool needs — and the ceiling your pipes impose.
Open calculatorTurnover
Find the pump flow rate your pool needs, and how long yours must run.
Open calculatorCost & Energy
Heating, electricity and maintenance costs.
Filling Cost
What it costs to fill your pool from the tap, at your own water rate.
Open calculatorHeating Cost
What it costs to heat your pool, at your own fuel prices.
Open calculatorOwnership Cost
Add up what a pool really costs you in a year — every figure your own.
Open calculatorPump Running Cost
What your pump costs to run, and what a variable-speed pump would save.
Open calculatorMaintenance
Schedules, cleaning and water care.
Start with your pool volume
Almost every other number depends on it. A chemical dose is volume multiplied by the change in parts per million; a turnover time is volume divided by flow rate; a heating cost is volume multiplied by the temperature rise. Get the volume wrong by a quarter and every dose you calculate afterwards is wrong by a quarter.
It is worth measuring rather than guessing, and worth writing down once. Most people only need to do it properly a single time. If your pool has a shallow end and a deep end, measure both and let the calculator average them — using the deep end alone is the most common reason a dose comes out too high.
A builder’s figure is often the volume at the rim rather than at the waterline, and pools are rarely filled to the rim. If your own measurement comes out five to ten per cent under the number you were given, that is usually why.
Which one you need
| If you are asking | Use |
|---|---|
| How much water is in here? | Pool Volume |
| My test kit shows several readings off | Water Health Check |
| How much chlorine do I add? | Chlorine, or Pool Shock if it has got away from you |
| How long should the pump run? | Turnover |
| What is this costing me? | Pump Running Cost, then Ownership Cost |
| What size equipment do I need? | Pump Size, Filter Size, Heater Size |
What the results assume
Every result here is an estimate built on published constants: 8.34 pounds per gallon of water, 7.48 gallons per cubic foot, and the strengths printed on standard pool chemicals. Those are reliable. What varies is your pool: sunlight, bather load, rain, and how accurate your test kit is.
So treat a dose as a starting point rather than a final answer. Add roughly three quarters of what a calculator suggests, let the water circulate for a few hours, then test again. You can always add more; getting a level back down is slower, more expensive and sometimes means draining water.
The product label wins every time. Concentrations differ between brands and change between batches, and the label is the one that was measured. If a label disagrees with a figure here, follow the label.
Common questions
Do I need to sign up to use these?
No. There is no account, no email required and no limit on how many times you use them. Nothing you type is sent anywhere — the arithmetic runs in your own browser.
Do they work in metric?
Yes. Every calculator has a switch between US units and metric, and the results show both — gallons alongside litres, pounds alongside kilograms. The Unit Converter handles anything the others do not.
How accurate are the chemical doses?
The arithmetic is exact for the strength you select. The uncertainty is in the inputs: your volume estimate and your test reading. A drop-based test kit is considerably more accurate than strips for chlorine and stabiliser, and that difference matters more than anything the calculator does.
Can I use these for a hot tub or spa?
The volume and dosing maths is the same, so the numbers will be right. Be aware that the target ranges differ — a spa runs hotter, holds far less water and takes a much heavier bather load for its size, so levels move faster than the same dose would move them in a pool.