Pool Water Calculator
Calculate the volume of water in your pool in gallons from pool dimensions and shape. Enter values for instant results with step-by-step formulas.
Formula
Rectangular: V = L x W x Avg Depth x 7.48 gal/cu ft | Circular: V = Pi x r^2 x Depth x 7.48
Pool volume is calculated by finding the cubic feet of water the pool holds (using geometry for the pool shape), then converting to gallons by multiplying by 7.48052 (gallons per cubic foot). Average depth is used for pools with sloping bottoms.
Worked Examples
Example 1: Standard Rectangular In-Ground Pool
Problem: Calculate the water volume for a 30 ft x 15 ft rectangular pool with a shallow end of 3.5 ft and deep end of 8 ft. Water costs $5 per 1,000 gallons.
Solution: Average depth = (3.5 + 8) / 2 = 5.75 ft\nVolume in cubic feet = 30 x 15 x 5.75 = 2,587.5 cu ft\nVolume in gallons = 2,587.5 x 7.48 = 19,354 gallons\nFill cost = (19,354 / 1,000) x $5 = $96.77\nFill time at 540 gal/hr = 35.8 hours
Result: 19,354 gallons | 2,587.5 cu ft | $96.77 to fill | ~36 hours fill time
Example 2: Round Above-Ground Pool
Problem: Calculate water volume for an 18 ft diameter above-ground pool filled to 4 ft depth.
Solution: Radius = 18 / 2 = 9 ft\nVolume = Pi x 9^2 x 4 = 3.14159 x 81 x 4 = 1,017.9 cu ft\nVolume in gallons = 1,017.9 x 7.48 = 7,614 gallons\nWeight = 7,614 x 8.34 = 63,501 lbs = 31.8 tons
Result: 7,614 gallons | 1,018 cu ft | 31.8 tons of water
Frequently Asked Questions
How many gallons of water does an average swimming pool hold?
The average residential swimming pool holds between 10,000 and 30,000 gallons of water, though the range is wide depending on size and shape. A small plunge pool or spa might hold only 2,000 to 5,000 gallons. A typical 12 by 24 foot rectangular pool with an average depth of 5 feet holds approximately 10,800 gallons. A larger 20 by 40 foot pool with varying depths from 3 to 8 feet holds roughly 34,000 gallons. Above-ground pools typically range from 3,000 to 10,000 gallons depending on diameter and wall height. Olympic-size pools hold approximately 660,000 gallons. Knowing your exact pool volume is essential for proper chemical treatment and maintenance.
How do I calculate the volume of a pool with varying depths?
For pools with varying depths (which is most pools), the standard approach is to calculate the average depth by adding the shallow end depth and deep end depth and dividing by two. Then multiply length times width times average depth to get cubic feet, and multiply by 7.48 to convert to gallons. For pools with a flat shallow section that drops suddenly to a deep end (rather than a gradual slope), divide the pool into two sections and calculate each separately for greater accuracy. The gradual slope method using average depth works well for most residential pools. If your pool has a very irregular bottom profile, divide it into several sections, calculate each zone separately, and add them together for the total volume.
How much does it cost to fill a swimming pool with water?
The cost to fill a swimming pool varies based on local water rates and pool size. In the United States, the average water cost is about $4 to $6 per 1,000 gallons. A typical 20,000-gallon pool would cost approximately $80 to $120 to fill from a garden hose. However, water rates vary significantly by region. In drought-prone areas like California, rates can be $8 to $15 per 1,000 gallons, potentially costing $160 to $300 for the same pool. Some homeowners opt for water delivery by truck, which typically costs $200 to $600 per truckload of 6,000 to 8,000 gallons. Municipal sewer charges may also apply since some utilities charge sewer fees on all water consumed, so check if you can get a sewer credit for pool fills.
How long does it take to fill a swimming pool?
Filling time depends on your water flow rate, which varies by hose diameter and water pressure. A standard garden hose delivers about 8 to 12 gallons per minute, or roughly 540 gallons per hour. At this rate, a 15,000-gallon pool takes approximately 28 hours to fill, while a 30,000-gallon pool takes about 56 hours. Using two garden hoses simultaneously cuts the time roughly in half. A fire hydrant meter (available for rent from some water utilities) can deliver water much faster at 500 to 1,000 gallons per minute. Water delivery trucks can partially fill your pool quickly, with a typical truck holding 6,000 to 8,000 gallons. Never leave a filling pool unattended, and be aware that rapid filling in hot weather can cause thermal shock to the pool surface.
Why is knowing my pool volume important for chemical treatment?
Accurate pool volume is the foundation of proper chemical treatment because nearly all pool chemicals are dosed based on gallons of water. Adding too little sanitizer leaves the pool unsanitary and prone to algae growth, while adding too much can irritate skin and eyes, damage pool equipment, and waste money. Chlorine dosage is typically 1 to 3 ppm (parts per million), and achieving this requires knowing the exact volume. pH adjusters, alkalinity increasers, calcium hardness chemicals, algaecides, and shock treatments are all calculated per gallon. An error of even 20 percent in volume estimation can lead to chronically over-treated or under-treated water. Salt water pool systems also require precise salt levels of 2,700 to 3,400 ppm, and the initial salt charge is calculated directly from pool volume.
How do I calculate the volume of a circular or round pool?
For a circular or round pool, use the formula: Volume in cubic feet equals Pi (3.14159) times the radius squared times the average depth. The radius is half the diameter. Then multiply cubic feet by 7.48 to convert to gallons. For example, an 18-foot diameter above-ground pool with 4 feet of water depth: radius = 9 feet, so Volume = 3.14159 x 9 x 9 x 4 = 1,017.88 cubic feet, which equals 7,614 gallons. Most above-ground pools are circular, making this the most common calculation for those pool types. For very large circular pools or those with irregular depths, the average depth method works just as well as with rectangular pools.