Pool volume is the master number. Every chemical dose, every turnover calculation, every filter sizing decision starts with it. Pro operators memorize a handful of formulas and one constant — and can calculate any residential pool's volume in about 60 seconds.
The master formula
Volume (gallons) = Surface Area (ft²) × Average Depth (ft) × 7.48
The 7.48 is a conversion constant — there are 7.48 gallons in one cubic foot of water. Metric: Volume (liters) = Surface Area (m²) × Average Depth (m) × 1000.
Surface area by pool shape
| Shape | Formula |
|---|---|
| Rectangle | Length × Width |
| Circle | π × R² (π ≈ 3.14) |
| Oval | Length × Width × 0.785 |
| Kidney | (A + B) × Length × 0.45 |
| Freeform | Split into rectangles/circles, sum the parts |
For kidney pools, A is the width at the widest point and B is the width at the narrowest point.
Average depth for multi-depth pools
For pools with a shallow end, deep end, and transition, use:
Average depth = (Shallow depth + Deep depth) ÷ 2
This is approximate — good enough for dosing. If you need precision (sizing a filter for code), you can weight by surface-area ratios of each section.
Worked example: typical FL backyard pool
Pool: 32 ft × 16 ft rectangle, shallow 3 ft, deep 7 ft.
Surface area: 32 × 16 = 512 ft²
Average depth: (3 + 7) ÷ 2 = 5 ft
Volume: 512 × 5 × 7.48 = ~19,150 gallons
Worked example: kidney pool
Pool: Kidney, 28 ft long, widest 14 ft, narrowest 10 ft, uniform 5 ft deep.
Surface area: (14 + 10) × 28 × 0.45 = 302.4 ft²
Volume: 302.4 × 5 × 7.48 = ~11,310 gallons
Why as-built volume drifts from plans
Real-world volumes can differ from blueprints by ±5% due to:
- Plaster thickness variation
- Tile and grout displacement
- Steps and bench seats
- Swim-outs and sun shelves
- Spill-over spas and attached features
For a new pool where chemistry matters, verify volume using a water meter reading during fill (if available) or by dye-tracer methods on commercial pools. For dosing, calculated volume is almost always close enough.
Conversion constants to memorize
- 1 ft³ of water = 7.48 gallons = ~62.4 lbs
- 1 gallon = 3.785 liters
- 1 inch of depth over 1 ft² = 0.623 gallons
- π ≈ 3.14 (or 3.14159 for the precise)