Measuring your pool
- Measure the length and width of the water surface, inside the walls.
- Measure the water depth at the shallow end and the deep end, from the floor to the water line, not to the top of the wall.
- For a sloped bottom, average the two depths. For a hopper (a steep deep end), split the pool into two parts and add them.
- For freeform pools, use the builder’s surface area, or split the shape into rectangles and half-circles.
The constants
One cubic foot holds 7.48 US gallons. A circle’s area is π × r², which works out to 0.785 × diameter², and 0.785 × 7.48 = 5.87. Kidney pools use the industry approximation 0.45 × (big width + small width) × length. In metric, length × width × depth in metres gives cubic metres, and 1 m³ is 1,000 litres.
Check it once
Every dose scales with volume, so it is worth confirming. Add a known amount of salt or stabilizer, wait for it to dissolve, and compare the test change with what the calculator predicted. If 10 lb of salt raised salt by less than expected, your pool is bigger than you thought.