Pool Volume Calculator
Calculate water volume in gallons for rectangular or circular pools. Essential for chemical dosing and fill time estimates.
Pool Dimensions
Your Estimate
Pool Volume
0
gallons
Volume Visualization
The Math Behind the Calculator
Rectangular Pool Formula
Gallons = Length x Width x Average Depth x 7.5
7.5 gallons per cubic foot of water
Circular Pool Formula
Gallons = 3.14159 x (Radius)² x Average Depth x 7.5
Radius = Diameter / 2
Why Average Depth?
Most pools have varying depths from shallow to deep end. By averaging the two depths, we get a reasonable estimate for standard pool shapes. For pools with more complex bottom contours (diving wells, beach entries), the calculation is an approximation.
Why Knowing Your Pool Volume Matters
Chemical Dosing
All pool chemicals are dosed by gallons. Incorrect volume means incorrect dosing:
- Chlorine shock treatments
- Algaecide applications
- pH adjusters
- Calcium hardness increaser
Equipment Sizing
Pool equipment is rated by gallons:
- Pump flow rate (GPM)
- Filter capacity
- Heater BTU output
- Salt chlorinator cell size
Turnover Rate
Your pump should "turn over" all pool water every 8-12 hours. Divide your pool gallons by turnover time (in minutes) to find required GPM. Example: 15,000 gallons / 480 minutes = 31.25 GPM minimum.
Fill Time Estimation
Standard garden hose flow rate is approximately 9 gallons per minute (540 GPH). At this rate:
| Pool Size | Gallons | Fill Time (1 hose) |
|---|---|---|
| Small (12x24) | ~10,000 | ~18 hours |
| Medium (16x32) | ~20,000 | ~37 hours |
| Large (20x40) | ~30,000 | ~55 hours |
Pro Tip: Water Delivery
For new pool fills, consider hiring a water delivery truck (typically 6,000-8,000 gallons per load). While more expensive than city water, it fills the pool in hours instead of days, reducing risk of liner damage from extended exposure.
Frequently Asked Questions
How do I measure an irregular-shaped pool?
For kidney or freeform pools, divide the pool into simpler shapes (rectangles, circles), calculate each section separately, and add them together. Or multiply the longest length x widest width x average depth x 0.45 (shape factor).
How much does the water in my pool weigh?
Water weighs 8.34 lbs per gallon. A 20,000 gallon pool contains about 167,000 lbs (83 tons) of water. This is why proper structural engineering is critical for in-ground pools.
How much does it cost to fill a pool?
At typical water rates of $0.005-$0.015 per gallon, filling a 20,000 gallon pool costs $100-$300. Add startup chemicals (~$100-200) for total fill cost. Water delivery trucks cost $200-400 per load.