How to calculate pool square footage
surface sq ft = length × width (rectangle) · 0.785 × diameter² (round) · 0.785 × length × width (oval) · floor + walls = surface + perimeter × average depth
Pool square footage means one of three numbers, and each job needs a different one. The water surface is what a heater, heat pump or solar cover works with and what evaporates. The floor and walls are what you paint, plaster or tile. The perimeter, in running feet, is the waterline tile and the coping. A 16x32 rectangle has 512 sq ft of surface and a 96 ft perimeter; at 3.5 ft in the shallow end and 7.5 ft in the deep end (5.5 ft on average) the walls add 96 × 5.5 = 528 sq ft, so the floor and walls come to 1,040 sq ft.
| Pool | Surface (sq ft) | Perimeter (ft) | Floor + walls (sq ft) | Gallons |
|---|---|---|---|---|
| 12x24 | 288 | 72 | 684 | 11,850 |
| 14x28 | 392 | 84 | 854 | 16,130 |
| 15x30 | 450 | 90 | 945 | 18,510 |
| 16x32 | 512 | 96 | 1,040 | 21,070 |
| 18x36 | 648 | 108 | 1,242 | 26,660 |
| 20x40 | 800 | 120 | 1,460 | 32,910 |
| Diameter | Surface (sq ft) | Perimeter (ft) |
|---|---|---|
| 12 ft | 113.1 | 37.7 |
| 15 ft | 176.7 | 47.1 |
| 18 ft | 254.5 | 56.5 |
| 21 ft | 346.4 | 66.0 |
| 24 ft | 452.4 | 75.4 |
| 27 ft | 572.6 | 84.8 |
| 30 ft | 706.9 | 94.2 |
Formulas by pool shape
Oval pools are true ellipses, so they take the same 0.785 (π ÷ 4) as round ones: an 18x36 oval has 509 sq ft, not the 648 of an 18x36 rectangle. A Roman pool is a rectangle with a half circle at each end. A kidney is close to 0.45 × (wide width + narrow width) × length, the factor the pool trade uses for gallons. An L-shape is two rectangles added. For a free-form pool, the average of several widths times the length gets within a few percent; the more widths you measure, the closer it gets. Kidney and free-form walls have no simple perimeter, so the floor and walls use the paint maker's shape factor instead: length × widest width × 1.6.
Use the surface in the pool heat pump calculator and the pool heating cost calculator, and for the water lost each day in the pool evaporation calculator. The floor and walls go into the pool paint calculator and the pool resurfacing cost calculator. For the water itself, the pool volume calculator gives the gallons of every shape and saves your pool for the chemical calculators.
Geometry: circle and ellipse area π ÷ 4 × length × width; ellipse perimeter by Ramanujan's approximation; kidney factor 0.45 as in the pool trade's gallon formula. Floor + walls treat the floor as flat, so a sloped floor adds a little. Shape factor 1.6 for free-form pools: Kelley Technical Coatings, Bulletin No. 143 "Estimating the Quantity of Coating Required" (02-10). Read October 23, 2026.
Frequently asked questions
How do I calculate the square footage of a pool?
Measure inside at the water line. Rectangle: length × width. Round: 0.785 × diameter × diameter. Oval: 0.785 × length × width. Kidney: 0.45 × (wide width + narrow width) × length. That is the water surface; for paint or plaster add the walls, perimeter × average depth.
How many square feet is a 15x30 pool?
450 sq ft of water surface, with a 90 ft perimeter. At a 5.5 ft average depth the walls add 495 sq ft, so the floor and walls to paint or plaster come to 945 sq ft. The pool holds about 18,510 gallons at that depth.
How many sq ft is an 18x36 pool?
An 18x36 rectangle has 648 sq ft of surface and a 108 ft perimeter; with a 5.5 ft average depth the floor and walls are 1,242 sq ft. An 18x36 oval is smaller: 0.785 × 18 × 36 = 509 sq ft of surface.
What is the square footage of a 16x32 pool?
512 sq ft of water surface and a 96 ft perimeter. At 3.5 ft in the shallow end and 7.5 ft in the deep end, the floor and walls are 1,040 sq ft. Size a heater, heat pump or solar cover from the 512, paint or plaster from the 1,040.
How do you measure a kidney-shaped pool?
Measure the length from end to end, then the width across the wide lobe and across the narrow lobe. Area ≈ 0.45 × (wide width + narrow width) × length: a 30 ft kidney that is 14 ft and 10 ft wide has about 324 sq ft of surface.