Pool Volume Calculator: How Many Gallons or Litres Is My Pool?
Select a shape and enter the pool’s actual water dimensions to see its estimated capacity instantly. This pool gallons calculator reports pool water volume in US gallons, Imperial gallons and litres for common and irregular shapes.
How to measure and calculate pool capacity
- Measure at the waterline. Measure inside length, width or diameter and water depth—not outside coping, wall height or empty freeboard.
- Choose the shape and units. Select the closest regular shape; use L-shaped or custom sections when one outline is not accurate.
- Choose the depth profile. Use Uniform depth for a flat floor or Shallow-to-deep slope for a gradual, even slope.
- Review the estimate. Check the substituted formula, then use the clearly labelled US gallons, Imperial gallons or litres value.
Shape formulas
- Rectangle:
surface area = length × width - Round:
surface area = π × (diameter ÷ 2)² - Oval:
surface area = π × (length ÷ 2) × (width ÷ 2) - Kidney:
surface area = 0.45 × (width A + width B) × length - Triangle:
surface area = base × height ÷ 2 - L-shaped/custom: calculate non-overlapping section areas and add them.
Methodology and review
Method: the calculator derives plan surface area from the selected shape, multiplies it by uniform or average water depth, and converts the cubic volume. The international foot is exactly 0.3048 metre; one US gallon is exactly 3.785411784 litres and one Imperial gallon is 4.54609 litres.
Shape guidance follows established pool-industry practice: the two-width kidney formula and the practice of summing regular sections for irregular pools are documented by SwimmingPool.com, while Pentair demonstrates shape-specific dimension inputs. Expected uncertainty is usually driven by measurement precision and unmodelled steps, benches, coving, freeboard, curved corners and abrupt deep-end geometry.
References: NIST unit conversion factors; NIST international foot definition; SwimmingPool.com pool formulas; Pentair pool volume guidance.
Common pool capacity reference tables
Round above-ground pools
Assumption: circular pool filled to a uniform 4 ft (1.22 m) water depth. Measure actual water depth before using an estimate for dosing.
| Diameter | Assumed depth | US gallons | Litres |
|---|---|---|---|
| 15 ft | 4 ft | 5,288 | 20,016 |
| 18 ft | 4 ft | 7,614 | 28,823 |
| 24 ft | 4 ft | 13,536 | 51,241 |
Rectangular inground pools
Assumptions are stated per row and use a gradual slope or equivalent average depth. Abrupt hoppers should be split into sections.
| Pool size | Assumed average depth | US gallons | Litres |
|---|---|---|---|
| 12 × 24 ft | 5 ft | 10,772 | 40,776 |
| 16 × 32 ft | 5.5 ft | 21,065 | 79,740 |
| 20 × 40 ft | 6 ft | 35,906 | 135,921 |
Worked pool-volume examples
Round pool
An 18 ft round pool with 4 ft of water has area π × 9² = 254.47 ft² and holds about 7,614 US gal (28,823 L).
Oval pool
A 30 × 15 ft oval averaging 5 ft deep has area π × 15 × 7.5 = 353.43 ft² and holds about 13,219 US gal (50,040 L).
Kidney pool
A 30 ft kidney pool with widths A and B of 14 ft and 10 ft, averaging 5 ft deep, holds about 12,118 US gal (45,873 L): 0.45 × (14 + 10) × 30 × 5 × 7.48052.
Split-section pool
Two non-overlapping rectangles measuring 20 × 12 ft and 8 × 6 ft have 288 ft² total area. At a uniform 4 ft depth they hold about 8,618 US gal (32,621 L).
Practical measurement guidance
Steps, tanning ledges and benches
These features displace water, so a simple outside-outline calculation tends to run high. For a large tanning ledge, use a separate custom section with its own representative depth, or subtract its displacement outside this tool.
Abrupt depth changes and hoppers
Averaging shallow and deep depth is appropriate for a gradual, even slope. For a sharp drop, hopper or separate diving well, divide the pool into sections and estimate each depth zone separately.
Irregular and freeform pools
Trace the plan as several non-overlapping rectangles, circles or triangles and use Custom sections. A kidney outline should use two independent width measurements; do not substitute one width for both.
How to verify the estimate
Compare the result with builder drawings, manufacturer specifications or commissioning records. A metered fill is a strong real-world check: record the water meter before and after filling while accounting for every other use.
Chemical dose assumptions
The collapsed dose helper is a conversion tool, not a treatment recommendation. It uses the approximation 1 ppm = 1 mg/L in pool water, then adjusts the active mass by the product strength entered. Product formulation, density and label instructions control the real dose. Test water first, follow the product label, never mix chemicals and seek qualified pool-service guidance when uncertain.
Safety reference: CDC Pool Chemical Safety.
Pool volume FAQs
How many gallons are in a 16 by 32 foot pool?
A 16 by 32 foot rectangular pool averaging 5.5 feet deep holds about 21,065 US gallons, 17,540 Imperial gallons or 79,740 litres. Use measured water depth for your own pool.
How do I calculate a flat-bottom pool versus a sloped pool?
Use Uniform depth for a flat floor. For a gradual, even slope, use Shallow-to-deep slope; the calculator averages the two depths. Split an abrupt hopper or drop-off into separate sections.
Should I use above-ground pool wall height as the depth?
No. Measure the actual water depth from the waterline to the floor. Wall height includes unfilled space above the water and can overstate capacity.
How do I calculate an L-shaped pool?
Split the L into two rectangles that do not overlap, enter each rectangle's length and width, and the calculator adds their surface areas before applying the selected depth profile.
Do steps, benches and tanning ledges change pool volume?
Yes. They displace water, so a simple exterior-shape estimate is usually slightly high. Model a large ledge as a separate shallow section or check builder specifications or a metered fill.
What is the difference between US and Imperial gallons?
One US gallon is 3.785411784 litres; one Imperial gallon is 4.54609 litres. The result labels both clearly because they are not interchangeable.
How can I check a pool volume estimate?
Compare the estimate with builder or manufacturer specifications. For a stronger check, record a water-meter reading before and after a full fill, accounting for any other water used.
Limits
Every result is an estimate unless capacity is verified by a metered fill. Measurement error and features such as curved corners, steps, shelves, spas, coving, sloped sidewalls and unusual deep-end geometry can change the real pool water volume. Use a conservatively rounded measured capacity when following product labels.