Pool Gallon Calculator
Use this tool to estimate how many gallons of water your swimming pool holds. Choose your pool shape, add dimensions, and click calculate.
If your pool depth is uniform, just fill in shallow depth and leave deep depth blank.
Why pool gallons matter
If you have ever asked, “How many gallons are in my pool?”, you are asking exactly the right question. Pool volume is the foundation for almost every maintenance decision: chlorine dosing, shock treatment, algaecide use, stabilizer adjustments, salt additions, and even heating estimates.
A volume estimate that is off by 20% can cause under-treatment (cloudy water, algae, unsafe sanitizer levels) or over-treatment (wasted chemicals, irritated skin, and avoidable cost). This calculator gives you a quick and practical estimate based on pool shape and average depth.
How to use this calculator
- Select your unit system (feet or meters).
- Choose your pool shape.
- Enter the required dimensions.
- Add shallow depth and deep depth (or only one depth for uniform pools).
- Click Calculate Gallons to see estimated volume in US gallons and liters.
Pool volume formulas used
The calculator uses geometry-based estimates suitable for most residential pools:
| Pool Type | Volume Formula (Cubic Units) | Notes |
|---|---|---|
| Rectangular | Length × Width × Average Depth | Best for standard rectangular pools |
| Round | π × (Diameter ÷ 2)2 × Average Depth | For circular above-ground and inground pools |
| Oval | π × (Length ÷ 2) × (Width ÷ 2) × Average Depth | Good estimate for elliptical pool footprints |
| Custom Area | Surface Area × Average Depth | Useful when footprint is irregular but area is known |
Average depth formula
Average Depth = (Shallow Depth + Deep Depth) ÷ 2
If your pool has one constant depth, the average depth is simply that depth.
Measuring tips for better accuracy
- Measure length and width at the waterline, not deck edge.
- Take depth measurements from waterline to floor at several points.
- For sloped bottoms, use both shallow and deep depths.
- For irregular pools, calculate or estimate surface area first and use custom area mode.
- Round final gallons to the nearest 50–100 gallons for day-to-day chemical planning.
Example: quick gallon estimate
Suppose your pool is rectangular:
- Length: 30 ft
- Width: 15 ft
- Shallow depth: 3.5 ft
- Deep depth: 7.5 ft
Average depth = (3.5 + 7.5) ÷ 2 = 5.5 ft
Cubic feet = 30 × 15 × 5.5 = 2,475 ft³
Gallons ≈ 2,475 × 7.48052 = 18,514 gallons
What to do with your gallon number
Once you know pool gallons, you can:
- Set accurate sanitizer and shock doses.
- Estimate filter run-time needs more effectively.
- Predict heating time and energy use.
- Plan water replacement or partial drain/refill events.
- Reduce chemical waste and maintenance cost.
Common mistakes to avoid
- Using deck dimensions instead of waterline dimensions.
- Forgetting to average shallow and deep end depth.
- Assuming all ovals are rectangles (or vice versa).
- Ignoring measurement unit mix-ups (feet vs meters).
FAQ
Is this exact?
It is an estimate based on standard geometry. For most maintenance tasks, this is more than accurate enough. For precision-critical commercial use, consult construction drawings or a professional measurement service.
Are these US gallons?
Yes. The calculator reports US gallons and liters.
My pool has benches, tanning ledges, and curves. What should I use?
Use the custom area option if you know the water surface area, then use a carefully measured average depth. When in doubt, test and fine-tune chemical dosing based on water results.
Bottom line
Knowing how many gallons are in your pool is the single most useful number in pool care. Use the calculator above, save your result, and base your chemical decisions on that value. Consistent dosing based on correct volume makes your water clearer, safer, and less expensive to maintain.