Pool Volume Calculator

The short answer

A rectangular pool is length times width times average depth times 7.5 gallons per cubic foot. A 16 by 32 foot pool with an average depth of 5 feet holds 2,560 cubic feet — about 19,200 gallons. Average depth is the shallow and deep depths averaged, and freeform shapes need to be broken into sections rather than estimated from the outline.

What it depends on

Shape is where the estimate usually goes wrong, because an oval or kidney-shaped pool holds noticeably less than the rectangle that encloses it. The water level rather than the coping height is the correct depth reference, and most pools are filled to just below the top of the skimmer. Volume drives chemical dosing, pump sizing and heater capacity, so an error propagates into all three.

Where this stops being useful

This is a volume estimate and does not cover circulation, chemical balance, barrier requirements or electrical code, all of which are regulated. Pool barriers, drain covers and equipment bonding are safety items governed by code, and permits are usually required. A licensed pool contractor can specify a system. General information and planning only, not engineering, structural or code advice.

An average depth is only accurate when the pool floor is level or slopes gently from one end to the other. A pool with a deep end and a shallow end needs to be measured in sections, and the section method in this calculator handles that. Round shapes and steps and ladders each add volume that the basic calculation misses, and a pool with a slope can easily be ten percent more than the simple figure suggests. If the pump turnover matters to you — and it usually does — being wrong here means the filter is undersized or overworked.

Volume is the number that appears in every later decision about a pool: the pump, the filter, the heating, the chemical dosing and the water top-up schedule. It is worth getting from measurements rather than from the builder's brochure, because the two often differ on an irregularly shaped pool.

Pool volume determines the pump and filter capacity, which are sold by flow rate in gallons per hour. The rule of thumb is to turn the pool volume over once every eight hours, which gives the required flow rate; most pool codes require one and a half turnovers per day. Calculate the volume first, then size the equipment to it. If you are comparing a new liner or estimating chemical doses, volume also sets how much chlorine or acid a change needs — both scale directly with the water volume.

Almost everything in pool care is dosed per volume of water, so the number that matters most is how many gallons or litres your pool actually holds. Get that wrong and every chemical dose is wrong with it, which is why pool shops ask for the volume before selling you anything, and why an estimate from the pool's dimensions is worth doing properly. The arithmetic is a volume calculation with one refinement: the floor slopes, so the depth varies. For a constant-depth pool, length times width times depth gives the cubic feet, and multiplying by about seven and a half gives US gallons. For a typical pool with a shallow and a deep end, average the two depths before multiplying. A round pool uses the area of a circle, pi times the radius squared, rather than length times width. Real pools rarely match the geometry exactly. Roman ends, steps, a sun shelf, a spa spillover and a sloped floor all remove or add volume relative to a plain rectangular box, so the calculated figure is usually a little generous. Dosing charts handle this with ranges, and it is plainly safer to be slightly over than under on sanitizer, but a heavily shaped pool may hold enough less water to matter — check the builder's original specification if you can find it. This calculator gives volume in cubic feet, US gallons, litres and cubic metres for a rectangular or round pool with a sloped floor. It ignores steps, spas and attached features. Round the result sensibly for dosing, keep a note of the figure near the pump, and use it whenever you adjust chlorine, pH or stabiliser.

This calculator returns estimates for planning and general information only. It is not engineering, architectural, structural, electrical or code advice, and it cannot replace a qualified professional who has seen the site. Material quantities depend on the actual dimensions, the product you buy and local building codes, so confirm the figures before ordering materials or starting work, and always follow local regulations.