Calculate your swimming pool's water volume in gallons and liters. Supports rectangular, round, oval, kidney, and L-shape pools with variable depth.
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63,713 liters
| Gallons | 16,831 |
|---|---|
| Liters | 63,713 |
| Cubic Feet | 2,250.0 |
| Fill Time (garden hose) | 31.2 hours |
| Estimated Water Cost | $100.99 |
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Your pool volume in gallons is the foundation for nearly every pool maintenance decision. Chemical dosing, pump sizing, heater capacity, filter selection, and water replacement calculations all depend on accurate volume measurement. Overestimating volume leads to over-dosing chemicals, which can cause skin irritation, bleached swimwear, and corroded pool equipment. Underestimating leads to under-dosing, allowing algae growth, cloudy water, and potentially unsafe bacteria levels.
Pool professionals measure volume in US gallons. The conversion factor from cubic feet to gallons is 7.48052. This means every cubic foot of your pool holds approximately 7.48 gallons of water. Metric users can convert further: one US gallon equals 3.785 liters.
The rectangular pool is the simplest to calculate. Measure the length and width in feet, then determine the average depth. If your pool has a consistent depth (like many above-ground pools), use that single number. If it slopes from shallow to deep end, average the two depths: (shallow + deep) / 2.
Formula: Length x Width x Average Depth x 7.48 = Volume in gallons. Example: A 16 x 32 foot pool with 3-foot shallow end and 8-foot deep end has an average depth of 5.5 feet. Volume = 16 x 32 x 5.5 x 7.48 = 21,065 gallons.
For pools that are not perfectly rectangular but close (like a slightly rounded corner rectangle), this formula gives a good approximation. True freeform shapes require more complex methods or professional measurement.
Round pools are common in above-ground configurations. Measure the diameter (distance across the widest point) in feet. The formula uses pi (3.14159) and the radius (half the diameter).
Formula: Pi x Radius squared x Depth x 7.48 = Volume in gallons. Example: An 18-foot diameter round pool with 4-foot depth. Radius = 9 feet. Volume = 3.14159 x 81 x 4 x 7.48 = 7,613 gallons.
Oval pools use the ellipse formula: Pi x (Long Axis / 2) x (Short Axis / 2) x Depth x 7.48. This gives the exact volume for a true oval shape. Kidney-shaped pools do not have a precise mathematical formula because the shape varies by manufacturer. A reasonable approximation is 75 percent of the rectangular volume: Length x Width x Depth x 7.48 x 0.75. This accounts for the concave indentation that defines the kidney shape.
L-shaped pools can be calculated by dividing the pool into two rectangles, calculating each separately, then adding the volumes. Alternatively, you can approximate an L-shape as 85 percent of the bounding rectangle: Length x Width x Depth x 7.48 x 0.85. The accuracy depends on how much of the rectangle the L-shape actually fills.
Once you know your pool volume, you can estimate fill time. A standard garden hose delivers approximately 9 gallons per minute at typical residential water pressure (40-60 PSI). This equals 540 gallons per hour. Dividing your pool volume by 540 gives the approximate fill time in hours. A 20,000-gallon pool takes about 37 hours to fill with one hose.
Water costs vary dramatically by location. The US average is about $0.006 per gallon ($6 per 1,000 gallons). At this rate, filling a 20,000-gallon pool costs approximately $120. In high-cost areas like parts of California, rates can reach $0.015 per gallon, tripling the cost to $300. Many municipalities offer a sewer credit for pool fills since the water does not enter the sewer system. Call your water utility before filling to ask about credits or bulk fill rates.
Your pool pump should turn over the entire pool volume at least once per 8 to 12 hours. This is called the turnover rate. For a 20,000-gallon pool with an 8-hour turnover target, you need a pump that moves at least 2,500 gallons per hour (42 GPM). Undersizing the pump leads to poor circulation and water quality issues. Oversizing wastes electricity. A variable-speed pump is ideal because it can adjust flow rates to match filtration needs, saving 50 to 70 percent on electricity compared to a single-speed pump.
Pool heaters are also sized by volume. A gas heater rated at 400,000 BTU can raise a 20,000-gallon pool by about 1.5 degrees Fahrenheit per hour. A heat pump rated at 120,000 BTU raises the same pool by about 0.5 degrees per hour but uses much less energy. Solar heating systems are typically sized to cover 50 to 100 percent of the pool surface area in collector panels.
Evaporation occurs when water molecules at the pool surface gain enough energy to escape into the air as vapor. The rate of evaporation depends on four primary factors: water temperature, air temperature, humidity, and wind speed. Warmer water evaporates faster because more molecules have sufficient energy to escape. Lower humidity means the air can absorb more moisture. Wind removes the thin layer of humid air above the pool surface, allowing faster evaporation. In hot, dry, windy conditions, evaporation can exceed half an inch per day.
A pool with 500 square feet of surface area losing a quarter inch of water per day loses about 78 gallons daily. Over a 30-day summer month, that totals approximately 2,340 gallons. At half an inch per day, the loss doubles to 4,680 gallons per month. Over a 5-month swimming season, total evaporation loss can reach 10,000 to 25,000 gallons, costing $60 to $150 in water alone, plus the chemical cost of treating replacement water.
If your pool seems to be losing water faster than expected, perform a bucket test to distinguish normal evaporation from a leak. Fill a bucket with pool water and place it on the pool steps so the water level inside the bucket matches the pool water level. Mark both levels. Wait 24 to 48 hours without using the pool. If the pool level drops more than the bucket level, you likely have a leak. If both drop equally, the loss is evaporation.
Pool leaks can be subtle. A crack in the shell, a loose fitting in the plumbing, or a tear in a vinyl liner can lose hundreds of gallons per day. A pool losing more than half an inch per day consistently, regardless of weather, should be inspected for leaks. Professional leak detection costs $200 to $500 and uses pressure testing and electronic listening equipment to pinpoint the source.
A pool cover is the single most effective tool for reducing evaporation. Solar covers (bubble covers) float on the water surface and reduce evaporation by 90 to 95 percent. They also capture solar heat, raising water temperature by 5 to 15 degrees Fahrenheit for free. A solar cover for a 16x32 pool costs $50 to $200 and lasts 3 to 5 years. Automatic retractable covers cost $10,000 to $20,000 installed but offer the ultimate convenience and also serve as a safety barrier. Manual reel systems for solar covers cost $200 to $500 and make daily cover use practical.
Liquid solar covers are another option. These products create an invisible, ultra-thin layer of alcohol on the water surface that reduces evaporation by 15 to 40 percent. They are far less effective than physical covers but require zero effort. A monthly supply costs $10 to $25. For pool owners who will not use a physical cover, liquid covers provide some benefit at minimal cost.
Wind barriers reduce evaporation by slowing air movement across the pool surface. A fence, hedge, or wall on the prevailing wind side of the pool can reduce evaporation by 25 to 50 percent. Raised pool edges or a solid deck border also help by breaking wind flow.
Lowering water temperature reduces evaporation, though this conflicts with the goal of comfortable swimming. If you heat your pool, consider lowering the thermostat by 2 degrees. Each degree reduction decreases evaporation by approximately 10 to 15 percent. Maintaining a 78-degree pool instead of 82 degrees reduces evaporation noticeably and also saves on heating cost.
Running water features like fountains and waterfalls increases evaporation by exposing more water surface to air. The aerated, splashing water evaporates much faster than still water. If evaporation is a concern, run decorative water features only when the pool is in active use rather than continuously.
A typical residential pool holds 10,000 to 30,000 gallons. A small pool (12x24 ft, 5 ft average depth) holds about 10,800 gallons. A medium pool (16x32 ft) holds about 19,200 gallons. A large pool (20x40 ft) holds about 30,000 gallons. Above-ground pools typically hold 3,000 to 10,000 gallons.
For a rectangular pool: Length x Width x Average Depth x 7.48 = gallons. For a round pool: 3.14 x Radius squared x Average Depth x 7.48. For oval pools: 3.14 x Half Length x Half Width x Average Depth x 7.48. The 7.48 converts cubic feet to gallons.
A standard garden hose flows at about 9 gallons per minute (540 gallons per hour). A 15,000-gallon pool takes approximately 28 hours to fill. A 25,000-gallon pool takes about 46 hours. You can reduce fill time by using two hoses or a fire hydrant permit if your municipality allows it.
At the US average water rate of about $0.006 per gallon, filling a 15,000-gallon pool costs roughly $90, and a 25,000-gallon pool costs about $150. Rates vary significantly by region. Some water utilities offer a pool fill credit that waives sewer charges since the water does not enter the sewer system.
Chemical dosing is calculated per gallon of water. Adding too much chemical to a small pool is dangerous, while under-dosing a large pool leaves it unsanitary. Chlorine, pH adjusters, algaecides, and shock treatments all require accurate volume measurements. Even a 20% volume error leads to 20% incorrect dosing.
For a pool that slopes from shallow to deep end, average depth equals (shallow end depth + deep end depth) divided by 2. For a pool with a hopper bottom (flat shallow area, slope, flat deep area), measure the depth at three to four points and average them for better accuracy.
Pools lose 1/4 to 1/2 inch of water per day to evaporation, depending on temperature, humidity, and wind. A 500-square-foot pool losing 1/4 inch daily loses about 78 gallons per day or roughly 2,300 gallons per month. A pool cover reduces evaporation by 90 to 95 percent.
One US gallon equals 3.785 liters. Pool chemical products sold in the US use gallons, while international products use liters. A 20,000-gallon pool equals approximately 75,708 liters. When following chemical dosing instructions, always verify whether the label references US gallons, imperial gallons, or liters.
Rectangular: L x W x Depth x 7.48 = gallons
Round: Pi x (D/2)^2 x Depth x 7.48
Oval: Pi x (L/2) x (W/2) x Depth x 7.48
Kidney: L x W x Depth x 7.48 x 0.75
1 gallon = 3.785 liters
Every formula on this page traces to a federal agency, central bank, or peer-reviewed institution. We cite the rule-makers, not secondhand blogs.
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Calculations are for educational purposes only. Consult a qualified financial advisor for personalized advice.