How does the pool volume calculator work?
The pool calculator tells you how much water you need to fill pools of various sizes and depths. This is useful information that helps you estimate the cost of the water, as well as the amount of time you need to go from an empty pool to floating around with a cool drink in your hand. If you're wondering how many gallons your pool has, give this tool a try!
Please note that the pool volume calculator assumes that the depth of the pool changes evenly and gradually from one end to the other, as is generally the case. If this does not apply to your pool, figures computed by the pool calculator are still in the right ballpark.
How to use the pool calculator
- Select your unit system — Imperial (feet) for US/UK, or Metric (meters) for the rest of the world.
- Choose the pool shape — Rectangular/Square or Oval/Circle.
- Enter pool dimensions — length and width.
- Enter depths — shallow end and deep end. If your pool has a uniform depth, enter the same value in both fields.
- Optionally, check "Water Cost" and enter the price per 1,000 gallons (imperial) or per m³ (metric) to estimate your water bill.
- Click Calculate Volume.
Formulas behind the pool calculator
Rectangular / Square pool
The volume of a rectangular pool with a sloping bottom is calculated as:
V = L × W × (d₁ + d₂) / 2
- V — Pool volume
- L — Length of the pool
- W — Width of the pool
- d₁ — Depth at the shallow end
- d₂ — Depth at the deep end
The formula averages the two depths, which is equivalent to finding the volume of a prism with a trapezoidal cross-section.
Oval / Circle pool
For an oval or circular pool, the area of an ellipse replaces the rectangular area:
V = (π × L × W / 4) × (d₁ + d₂) / 2
The factor π/4 converts the bounding rectangle to the area of the inscribed ellipse. For a perfectly circular pool, L = W = diameter, and the formula simplifies to V = π × r² × avg_depth.
How many gallons is my pool?
Let's walk through an example with this pool volume calculator:
- Choose Rectangular shape and Imperial units.
- Enter 50 ft length and 12 ft width.
- Set shallow end depth to 4 ft and deep end to 6 ft.
- The calculator shows the volume: approximately 22,441 US gallons (84,955 liters, 84.95 m³).
At the US average water rate of $1.50 per 1,000 gallons, filling this pool costs around $33.66.
Volume unit conversions
| From | To US Gallons | To Liters | To m³ | To ft³ |
|---|---|---|---|---|
| 1 ft³ | 7.48052 gal | 28.3168 L | 0.028317 m³ | — |
| 1 m³ | 264.172 gal | 1,000 L | — | 35.3147 ft³ |
| 1 US gallon | — | 3.78541 L | 0.003785 m³ | 0.13368 ft³ |
Water weight
Knowing how much your pool water weighs helps with structural load calculations:
- 1 US gallon of water weighs approximately 8.34 lbs (3.785 kg).
- 1 liter of water weighs exactly 1 kg (at 4°C).
- A typical 22,441-gallon pool holds approximately 187,154 lbs (84,955 kg) of water — nearly 85 metric tons!
Olympic swimming pool volume
An Olympic swimming pool measures 50 m × 25 m × 2 m (uniform depth). Its volume is:
- 2,500 m³ (2,500,000 liters)
- 660,430 US gallons
- Water weighs approximately 2,500 metric tons
Typical residential pool sizes
| Pool Type | Typical Size (ft) | Avg Depth (ft) | Approx. Gallons |
|---|---|---|---|
| Small backyard | 10 × 20 | 4 | ~6,000 |
| Standard backyard | 12 × 24 | 4.5 | ~12,000 |
| Large backyard | 16 × 32 | 5 | ~24,000 |
| Lap pool | 10 × 50 | 4 | ~15,000 |
| Our example | 12 × 50 | 5 (avg) | ~22,441 |
FAQs
- How do I measure pool depth if it slopes?
- Measure the shallowest point (usually 3–4 ft) and the deepest point (usually 5–8 ft for residential pools). Enter both values into the calculator. It automatically averages them.
- My pool has a flat bottom — what do I enter for depths?
- Enter the same depth in both the shallow and deep end fields. The average will equal that depth and the calculation will be exact.
- How accurate is this calculator?
- The calculator is accurate for pools with a gradually sloping bottom. If your pool has a flat shallow end, a steep drop, and a flat deep end (a common shape), divide it into sections and calculate each separately, then sum the volumes.
- How much does it cost to fill a pool?
- Check the "Water Cost" option and enter your local water rate. In the US, the average is about $1.50 per 1,000 gallons. In Russia, water costs around 30–50 rubles per m³. Fill times depend on your water supply flow rate.
- How much water does an oval pool hold?
- An oval pool holds about 78.5% (π/4 ≈ 0.785) of the volume of a rectangular pool with the same length, width, and depth. Select "Oval / Circle" in the calculator to get the correct result.