Pool Calculator: Determine Gallons of Water to Fill Your Pool

Our pool calculator will compute how many gallons of water it will take to fill your pool. We’ve also provided a pool gallon formula for manual calculations.

Enter the length, width, and depth of the pool in feet. There are two spaces for depth, and this calculator works if your depth increases at an even rate. In the first depth field, enter the dimension of the shallowest area, and in the second depth field, enter the dimensions of the deepest end.

Use the following formula to calculate pool gallons for a rectangular or square pool with a shallow and deep end that increases at an even, gradual rate:

Pool volume in gallons = length (ft) x width (ft) x d1 (ft) + d2 (ft)2 x 7.5

To determine the pool volume in gallons for a square or rectangle pool with a constant depth, use the following formula, where the length, width, and depth are all in feet:

Pool volume in gallons = length (ft) x width (ft) x depth (ft) x 7.5

To determine the pool volume in gallons for a circular pool with a shallow end and a deep end that evenly changes, use the following formula:

Pool volume in gallons = 3.14 x radius squared (ft) x d1 (ft) + d2 (ft)2 x 7.5

The formula for pool gallons for a circular pool with a constant depth is:

Pool volume in gallons = 3.14 x radius squared (ft) x depth (ft) X 7.5

How to Calculate How Many Gallons of Water for a Rectangular or Square Pool: Examples

Determining the cubic footage is the first step in calculating the number of gallons to fill a pool. The formula for cubic footage is length x width x depth. Once you know the cubic footage, you can multiply that number by 7.5 since there are about 7.5 gallons in each cubic foot.

Calculating the pool volume of a standard rectangle or square pool with a constant depth is easy. In this example, we’ll calculate gallons of water to fill a 28’ x 14’ x 5’ pool.

Pool volume in gallons = 28 x 14 x 5 x 7.5

Based on this formula, it would take 14,700 gallons of water to fill this size pool.

To estimate pool volume in gallons for a pool with a shallow and deep end, you must calculate the average pool depth. We’ll do this by adding the shallow and deep end together and dividing by two.

(Note: This formula works for pools that gradually increase in depth. If your pool has a sudden drop-off, the results will be less accurate.)

For our example, we’ll calculate gallons of water for a 28′ x 14′ pool with a 3′ shallow end and a 6′ deep end. Here’s what the formula looks like:

Pool volume in gallons = 28 x 14 x 3 + 62 x 7.5

Based on this formula, filling a pool this size takes 13,230 gallons of water.

How to Calculate Gallons of Water for Circular Pools: Examples

To find the cubic feet of a circular pool, you must multiply pi by the radius squared by the average depth. Then multiply the total cubic footage by 7.5 to determine the number of gallons needed.

In this formula, we’ll use 3.14 to represent pi. To find the radius of your circular pool, divide the diameter in two. For example, if your pool is 24 feet in diameter, your radius is 12 ft. To find the radius squared, multiply the radius by the radius.

In this example, we’ll calculate pool volume in gallons for a pool with a 24 ft diameter (12-foot radius) and a constant depth of 4 feet.

Pool volume in gallons = 3.14 x 12 x 12 x 4 x 7.5

Based on our calculations, it would take 13,565 gallons of water to fill a pool this size.

If you have an in-ground circular pool that evenly changes depth from the shallow end to the deep end, you must figure out the average depth to determine pool volume in gallons.

In this example, we’ll calculate pool volume in gallons for a circular inground pool with a 36-foot diameter (equal to an 18-foot radius), a shallow end of 3 feet, and a deep end of 5 feet.
Pool volume in gallons = 3.14 x 18 x 18 x 3 + 52 x 7.5

Based on our calculations, a pool this size requires 30,521 gallons of water.

How to Estimate How Much It Will Cost to Fill Your Pool

Using a garden hose to fill your pool costs $4 – $10 per 1,000 gallons of water. To determine total costs, use one of the formulas above to estimate the gallons you need. Then divide that number by 1,000 and multiply by $4 and $10 for an average range.

• 10,000-gallon pool – $40 – $100
• 15,000-gallon pool – $60 – $150
• 20,000-gallon pool – $80 – $200
• 25,000-gallon pool – $100 – $250
• 30,000-gallon pool – $120 – $300
• 35,000-gallon pool – $140 – $350

The cost of water delivery service is more expensive than filling your pool with a hose, costing anywhere from $500 – $2,000+ depending on your pool size and location.