Last updated: March 2026
What Is the Pool Gallons Calculator?
The Pool Gallons Calculator determines exactly how many gallons of water your swimming pool contains. Whether you have a rectangular in-ground pool, a round above-ground pool, an oval pool, or an L-shaped design, this tool handles the geometry and gives you an accurate gallon count in seconds. Knowing your pool's volume is the foundation of every maintenance task, from chemical dosing to estimating fill time and water costs.
Beyond the gallon calculation, the tool provides a complete chemical dosing guide for initial pool fills, weekly maintenance chlorine amounts, and a monthly cost estimate. The hot tub mode lets you quickly calculate chemical amounts for smaller volumes using common spa size presets.
Pool Gallons by Shape
Rectangular pools are the most common shape. Multiply length times width times average depth, then multiply by 7.48 to convert cubic feet to gallons. A 30 by 15 foot pool at 5 feet deep holds about 16,830 gallons.
Circular pools are popular for above-ground installations. The formula uses pi times the radius squared times depth times 7.48. An 18-foot diameter round pool at 4 feet deep holds approximately 7,634 gallons.
Oval pools combine the aesthetics of a round pool with the swim length of a rectangular one. The formula multiplies pi times the long radius times the short radius times depth times 7.48.
L-shaped pools are calculated as the sum of two rectangular sections. Measure each section separately, calculate each volume, and add them together for the total.
Frequently Asked Questions
How many gallons of water does a typical pool hold?
A typical residential in-ground pool holds between 10,000 and 30,000 gallons. A standard 12 by 24 foot pool with an average depth of 5 feet contains about 10,780 gallons. Larger pools of 20 by 40 feet at 5.5 feet deep hold around 32,900 gallons. Above-ground pools are usually smaller, ranging from 3,000 to 10,000 gallons depending on size.
How do I find out how many gallons my pool holds?
Measure the pool length, width, and average depth in feet. For rectangular pools, multiply length times width times average depth times 7.48. For round pools, use pi times the radius squared times depth times 7.48. Enter your measurements into this calculator and it handles the math for all pool shapes automatically.
How long does it take to fill a swimming pool?
At a standard garden hose flow rate of about 480 gallons per hour, a 15,000-gallon pool takes roughly 31 hours to fill. Running two hoses cuts that time in half to about 16 hours. Actual fill time depends on your water pressure, hose diameter, and how many fixtures are sharing the water supply while filling.
How much chlorine do I need for my pool size?
For an initial fill, use about 2 ounces of granular chlorine per 10,000 gallons to establish a baseline level of 1 to 3 parts per million. For weekly maintenance, add about 1 ounce per 10,000 gallons. Always test chlorine levels with a kit or strips before adding more, as sunlight, temperature, and bather load all affect how quickly chlorine dissipates.
Does pool shape affect the volume calculation?
Yes, the formula changes with each shape. Rectangular pools use length times width. Circular pools use pi times radius squared. Oval pools use pi times the long radius times the short radius. All formulas then multiply by average depth and by 7.48 to convert cubic feet to gallons. Using the wrong shape formula can produce errors of 20 percent or more.