How to Measure Your Swimming Pool
Measure length, width, diameter and average depth accurately, including sloped floors, steps and freeform outlines.
· 8 min read
A volume figure is only as good as the tape measure behind it. This guide explains where to stand, what to record, and how to turn a sloped floor into a single average depth you can type into the pool volume calculator.
What you need
- A tape measure long enough for the longest side (30 m / 100 ft is plenty for most domestic pools).
- A telescopic pole or a marked pole for depth, if you cannot reach the floor by hand.
- A notepad, or the calculator open on your phone.
Measure the water surface, not the coping. Tiles, raised beams and overflow channels sit outside the water and should not be included in length or width.
Rectangular pools
Measure the inside length along one long wall, then the inside width at both ends. If the two width readings disagree by more than a couple of centimetres, average them — many older pools are slightly out of square. Record the unit you used (metres, feet, centimetres or inches) and keep it consistent.
Circular and oval pools
For a circle, measure the diameter across the centre in two directions and average them. For an oval, measure the longest inside length and the widest inside width. The calculator treats an oval as an ellipse, so those two figures become the full axes (it halves them for you).
Average depth, including a slope
Take both readings at the centreline of the pool, from the water surface to the floor — not to a step tread. If the floor has a hopper or more than one slope, take three or more depth readings along the centreline and average those instead.
Steps, benches and beach entries
Roman steps and sun shelves hold extra water that a simple rectangle misses. Measure the shelf as its own shallow rectangle (length × width × shelf depth) and add it with the irregular shape mode. Ignore the thickness of the step risers; they displace a trivial volume compared with the basin.
Irregular and kidney outlines
Walk the outline and sketch it as overlapping rectangles, circles and ovals. Measure each piece as if it were a pool on its own, then add the sections. Overlap is better than a gap: a slight overestimate is safer for chemical dosing than an underestimate.
When the numbers are in, calculate the volume and keep a note of the date. Re-measure after a major remodel, a change of liner, or if you start using a different unit on product labels.
Next: the exact formulas with worked examples, or a litres-to-gallons conversion.