Why use this calculator
Every pool chemical is dosed per volume of water, so an accurate figure is the difference between clear water and either a green pool or an over-chlorinated one. Most owners either do not know their volume or are working from a number a previous owner mentioned once, and errors of twenty or thirty per cent are common because average depth is not the same as deep-end depth.
This calculator handles the three common shapes, averages the depth correctly for a sloping floor, and converts the result straight into the chlorine and salt quantities you actually need, which is the form the question is usually asked in.
How to use it
- Choose the shape that matches your pool.
- For a round pool enter the diameter as the length; for an oval enter the long and short axes.
- Measure water depth rather than wall height, since the waterline typically sits well below the coping, and enter both the shallow and deep end figures so the calculator can average them.
- For a flat-bottomed pool put the same figure in both.
- Measure at the water surface for length and width, and use metres throughout.
- The results are converted to gallons for anyone working from American product labels.
What each result means
- Pool volume
- Total water capacity in litres. The figure every chemical dose is calculated against.
- In cubic metres
- The same volume in cubic metres, which is how pool builders and water carters usually quote.
- In US gallons
- The volume in US gallons, needed when following American product labels or equipment specifications.
- Surface area
- The water surface area, used for sizing covers, solar heating and evaporation estimates.
- Average depth
- The mean of the shallow and deep ends. Using the deep-end figure alone would overstate volume substantially.
- Liquid chlorine to raise free chlorine by 1 ppm
- How much 12.5 per cent liquid chlorine adds one part per million. Multiply by the increase you need, and always check the product label.
- Granular chlorine for 1 ppm (65% available)
- The equivalent dose in granular calcium hypochlorite, which is more concentrated and must be dissolved before adding.
- Salt to reach 4,000 ppm from zero
- Salt required for a chlorinator pool starting from fresh water. An existing pool needs only the shortfall.
The formula
Volume is surface area multiplied by average depth. Surface area is length × width for a rectangle, π × radius² for a round pool, and π × (long axis ÷ 2) × (short axis ÷ 2) for an oval. Average depth is the shallow and deep end depths averaged, which is exact for a floor that slopes uniformly. One cubic metre is 1,000 litres and 264.17 US gallons. For dosing, raising free chlorine by 1 part per million in 10,000 litres requires about 10 grams of pure available chlorine, which is 80 millilitres of liquid chlorine at 12.5 per cent available.
How this number is used in practice
Using deep-end depth instead of average depth is the most common error, and it overstates volume by a third on a typical pool with a sloping floor. That error runs straight into every chemical dose, leaving the water persistently under-treated. Which is usually diagnosed as a pump or filter problem when it is arithmetic. If you only ever measure one thing accurately, make it the depth at both ends.
Dosing is not a one-off calculation. Chlorine is consumed by sunlight, swimmers and organic matter, so free chlorine is typically held between one and three parts per million and topped up continuously. Stabiliser, or cyanuric acid, slows the sun's destruction of chlorine but at too high a level it makes the chlorine sluggish. pH matters just as much: above about 7.8 chlorine loses much of its effectiveness regardless of how much you add.
Volume also drives equipment sizing and water costs. A pump and filter should turn the whole volume over roughly every six to eight hours, and heating, covers and solar systems are specified per volume or surface area. Filling a 50,000 litre pool from mains water is a substantial bill in most Australian councils, which is worth knowing before draining one for maintenance.
Worked examples
8 m by 4 m rectangular pool, 1.1 m shallow and 2.0 m deep
About 49,600 litres, or 49.6 cubic metres, needing roughly 0.4 litres of liquid chlorine per part per million.
4 m diameter round pool, 1.2 m deep throughout
About 15,100 litres. A flat-bottomed pool uses the same depth at both ends.
10 m by 5 m oval pool, 1.2 m shallow and 1.8 m deep
About 58,900 litres. An oval holds roughly 79 per cent of the rectangle enclosing it.
When people use it
- Working out chemical doses accurately instead of guessing
- Sizing a pump, filter or heater to your pool
- Calculating salt for a chlorinator when commissioning or refilling
- Estimating the water cost of filling or topping up
- Checking a pool builder's stated capacity against the measurements
Tips
- Measure water depth, not wall height. The waterline usually sits well below the coping.
- Average the shallow and deep ends. Using the deep end alone overstates a typical pool by about a third.
- Free chlorine is normally held between 1 and 3 ppm, with pH between 7.2 and 7.6 for it to work properly.
- Above pH 7.8 chlorine loses much of its effectiveness no matter how much you add.
- Add chemicals with the pump running and never mix concentrated products together.
- An oval holds about 79 per cent of the rectangle that would enclose it. A useful mental check.
What it assumes, and where it stops being accurate
- The floor is assumed to slope uniformly between the shallow and deep ends.
- Kidney, freeform and L-shaped pools are approximated by breaking them into simpler shapes.
- Steps, benches, swim-outs and spa spillovers are not deducted and reduce actual volume slightly.
- Chlorine dosing assumes 12.5 per cent available liquid chlorine and 65 per cent granular; check your product.
- Stabiliser level, pH, temperature and chlorine demand all affect real dosing and are not modelled.
- The salt figure assumes a target of 4,000 ppm from fresh water; check your chlorinator's recommended range.
Terms used on this page
- Free chlorine
- The chlorine available to sanitise the water, as distinct from chlorine already combined with contaminants.
- Parts per million (ppm)
- A concentration measure: 1 ppm is one gram of substance per 1,000 litres of water.
- Stabiliser
- Cyanuric acid, which slows the sun's destruction of chlorine but reduces its speed at high levels.
- Turnover rate
- How long the pump takes to circulate the entire pool volume through the filter.
Questions people ask
- How do I calculate my pool volume?
- Multiply the surface area by the average depth. For a rectangular pool that is length × width × ((shallow + deep) ÷ 2). An 8 by 4 metre pool averaging 1.55 metres deep holds about 49,600 litres. Round pools use π × radius² for the area, and ovals use π × half the long axis × half the short axis.
- Should I use the deep end depth?
- No. Use the average of the shallow and deep ends. Using the deep-end figure alone overstates volume by around a third on a typical sloping-floor pool, and that error carries straight into every chemical dose, leaving the water chronically under-treated.
- How much chlorine does my pool need?
- Free chlorine is normally held between one and three parts per million. Raising it by one part per million takes roughly 80 millilitres of 12.5 per cent liquid chlorine per 10,000 litres, so a 50,000 litre pool needs about 400 millilitres. Demand rises sharply with heat, rain, swimmer load and sunlight.
- How much salt does a salt chlorinator pool need?
- Most chlorinators target between 3,000 and 5,000 parts per million, so a 50,000 litre pool starting from fresh water needs around 200 kilograms at 4,000 ppm. An established pool only needs the shortfall, since salt is not consumed. It is only lost through splash-out, backwashing and rain overflow.
- How do I measure an irregular or kidney-shaped pool?
- Break it into simpler shapes, calculate each and add the results. A kidney shape is often approximated as two overlapping circles or as an oval with a correction. For an unusual shape, taking the average of the widest and narrowest widths and treating it as a rectangle usually lands within ten per cent.
- Why does pH matter as much as chlorine?
- Because chlorine's sanitising power depends on it. Above about pH 7.8 much of the chlorine converts to a far less effective form, so a pool can show adequate chlorine on a test and still go green. Keeping pH between 7.2 and 7.6 is what lets the chlorine you have added actually work.
Use this with
Swimming Pool Volume Calculator answers one part of the question. These pick up where it stops: Water Tank & Dam Volume Calculator, Area Calculator, Mulch, Soil and Gravel Calculator and Power Bill Calculator.
Where these figures come from
This calculation is jurisdiction-neutral arithmetic. No country-specific rules are applied.
- Royal Life Saving Australia: home pool safety. Pool safety and supervision guidance
- NSW Health: swimming pool water quality. Chlorine and pH guidance for domestic pools
Swimming Pool Volume Calculator produces an estimate for general information. It is not financial, tax, medical, legal or engineering advice. read the full disclaimer. Spotted a wrong number? Report it and it gets fixed. The form picks up this calculator and the inputs you used.