Pool Calculator

How to use the pool volume calculator

What this calculator does

This calculator estimates how much water a rectangular, square, oval, or circular pool can hold. It combines the pool's plan area with the average of two end depths, then reports capacity in gallons or liters, surface area, cubic volume, approximate water weight, and an optional fill-cost estimate. The calculation is most accurate for pools whose floor slopes gradually and evenly between the two measured depths. It is a planning estimate, not a survey of irregular steps, tanning ledges, curved walls, displaced equipment, or the lower operating waterline used in a real pool.

When to use it

Use the calculator when planning a first fill, checking a contractor's stated capacity, selecting pumps or treatment products that are sized by water volume, or comparing water costs before opening a pool. It is also useful when converting a capacity stated in liters to US gallons, or when you know the dimensions but the pool documentation is unavailable.

How to calculate

1. The calculator opens with a ready-to-use demonstration: a 50 ft by 12 ft rectangular pool that slopes from 4 ft to 6 ft. The example results and a validated Excel workbook are available immediately.
2. Choose Pool shape. Select Rectangular / square for straight sides and square corners, or Oval / circle when the top view is an ellipse or circle.
3. Choose the Measurement system. Switching between feet and meters converts the current dimensions rather than merely changing the labels.
4. Replace Length, Width, Depth 1, and Depth 2 with positive measurements. For a level-bottom pool, enter the same depth twice. For a gradual slope, enter the shallow and deep ends.
5. Optionally enter Water price per 1,000 gallons. In metric mode the same rate is shown and entered per 1,000 liters, then converted consistently for the cost calculation.
6. Read Pool volume first, then review Cubic volume, Average depth, Surface area, Estimated water weight, Estimated fill cost, and Equivalent liters or gallons. The details table shows both systems side by side.
7. Select Download Excel to create a current-state workbook. Reset clears the demonstration and calculated output; export remains unavailable until all four required dimensions form a valid pool again.

Input guide

Pool shape is required. The rectangular option uses length × width for surface area. The oval option uses π × length × width ÷ 4. Choosing oval therefore reduces volume for the same bounding length and width. Do not choose oval merely because a rectangular pool has rounded corners; use the plan shape that best represents most of the water surface.

Measurement system is required and accepts either feet with US gallons or meters with liters. NIST explains that the cubic meter is the SI volume unit and that one liter is one cubic decimeter in its SI units guidance for volume. Switching systems preserves the physical pool by converting every dimension.

Length and Width are required positive decimals. Enter plain en-US numbers such as 50, 12.5, or 1,250.25; commas may be used only as thousands separators. Scientific notation and decimal commas are rejected. Measure at the intended waterline, not necessarily the outside edge of coping. Larger length or width increases volume in direct proportion.

Depth 1 and Depth 2 are required positive decimals measured from the intended water surface to the floor. A 4 ft shallow end and 6 ft deep end produce a 5 ft average depth. Reversing the two values does not change volume. Abruptly stepped or multi-level floors should be divided into simpler sections and added separately.

Water price per 1,000 gallons is optional and accepts zero or a positive US-dollar amount such as 1.50. Use the rate that applies to the incremental water consumed; some utilities also charge sewer or fixed fees, so the displayed cost may not match the entire bill. In metric mode, the label changes to price per 1,000 liters and the numeric rate is converted to preserve the same cost basis.

Output guide

Pool volume is the primary theoretical capacity. Cubic volume shows the same space in ft³ or m³. Average depth is the arithmetic mean of the two depths. Surface area is the top-view water area and is useful for cover sizing and evaporation planning. Estimated water weight uses standard water density as an approximation and should not be used as a structural engineering load calculation. Estimated fill cost multiplies capacity by the entered unit rate; it displays an em dash when no rate is supplied. Equivalent liters or gallons is an exact unit conversion at the calculator's stored precision. The summary pills repeat shape, average depth, and capacity from the same model.

Worked example

The startup pool is rectangular, 50 ft long, 12 ft wide, 4 ft at one end, and 6 ft at the other. Average depth is (4 + 6) ÷ 2 = 5 ft. Surface area is 50 × 12 = 600 ft². Cubic volume is 600 × 5 = 3,000 ft³. Multiplying by 7.48051948 US gallons per cubic foot gives 22,441.57 US gallons. At $1.50 per 1,000 gallons, the estimated fill cost is 22,441.57 ÷ 1,000 × $1.50 = $33.66. The same water is about 84,949 liters.

Learn more

A pool's theoretical fill is only one part of water planning. The U.S. EPA's pool water-efficiency guidance explains how covers can reduce evaporation and replacement water. For safe operation after filling, consult the CDC's home pool water treatment and testing guidance for current disinfectant and pH recommendations.