The formulas
- Rectangle: length × width × average depth × 7.48
- Round: π × (diameter ÷ 2)² × average depth × 7.48
- Oval: length × width × 0.785 × average depth × 7.48
- Kidney: (width A + width B) × length × 0.45 × average depth × 7.5
Average depth is (shallow + deep) ÷ 2 for a steadily sloped floor; hopper-bottom or deep-end pools run a little off, so treat the answer as ±5–10%. There are 7.48 US gallons in a cubic foot.
Why surface area matters for robots
A robot doesn't care how many gallons you have. It cares about the floor it has to cover, thewalls it has to climb and whether it needs to scrub the waterline. A shallow 16×32 ft pool and a deep 16×32 ft pool have the same floor but very different wall area, so size up for deep pools and heavy debris. Take your floor area to the robot matcher, or readhow robot coverage ratings work.
FAQ
How do I calculate pool volume in gallons?
For a rectangular pool: length × width × average depth × 7.48. Average depth is (shallow depth + deep depth) ÷ 2 for a sloped floor. Round pools use π × radius² × depth × 7.48; ovals use length × width × 0.785 × depth × 7.48; kidney pools use (A + B) × length × 0.45 × depth × 7.5.
How big a robot do I need for my pool volume?
Robots clean surfaces, not volume, so floor area matters more than gallons. Pick a cordless robot rated for roughly 1.5× your floor area, or a corded robot rated for a pool longer than yours. The robot matcher does this for you.