If you own a swimming pool, knowing how many gallons of water it holds is essential for tasks like chemical balancing, heating cost estimation, and even water refills. That’s where a Gallon Pool Calculator becomes an indispensable tool. Whether you have a rectangular, circular, oval, or irregular pool, this calculator helps you estimate the total volume in gallons accurately using basic pool measurements.
Gallon Pool Calculator
A swimming pool’s water volume is measured in gallons. Accurately calculating this volume helps you:
- Add the correct amount of pool chemicals
- Estimate filling costs
- Determine pump sizes and flow rates
- Schedule maintenance more efficiently
The Gallon Pool Calculator lets you input your pool’s dimensions—such as length, width, average depth, and shape—to instantly calculate how many gallons of water your pool can hold.
It supports common pool shapes including:
- Rectangular
- Round (circular)
- Oval
- Custom/irregular (approximation)
🔧 How to Use the Gallon Pool Calculator
Step-by-Step Instructions:
- Select Your Pool Shape:
Choose from rectangular, circular, oval, or freeform (custom). - Enter Pool Dimensions:
- Rectangular Pool: Length, Width, Average Depth
- Round Pool: Diameter, Average Depth
- Oval Pool: Long Diameter, Short Diameter, Average Depth
- Irregular Pool: Approximate Area and Average Depth
- Click “Calculate” to get the total volume in gallons.
The result gives you an accurate estimate of the water your pool can hold, rounded to the nearest gallon.
📐 Gallon Calculation Formulas
Each pool shape uses a specific formula to calculate volume in gallons:
1. Rectangular Pool:
Formula:
Length × Width × Average Depth × 7.5 = Gallons
2. Round Pool:
Formula:
Diameter × Diameter × Average Depth × 5.9 = Gallons
3. Oval Pool:
Formula:
Long Diameter × Short Diameter × Average Depth × 5.9 = Gallons
4. Irregular/Freeform Pool:
Formula:
Surface Area × Average Depth × 7.5 = Gallons
(Surface area estimated by length × width of the widest points)
Note: 1 cubic foot = 7.5 gallons. This is the key conversion factor.
🧮 Example Calculations
Example 1: Rectangular Pool
- Length: 30 ft
- Width: 15 ft
- Average Depth: 5 ft
Calculation:
30 × 15 × 5 × 7.5 = 16,875 gallons
Example 2: Round Pool
- Diameter: 24 ft
- Average Depth: 4.5 ft
Calculation:
24 × 24 × 4.5 × 5.9 = 15,309.6 gallons
Example 3: Oval Pool
- Long Diameter: 30 ft
- Short Diameter: 15 ft
- Average Depth: 5 ft
Calculation:
30 × 15 × 5 × 5.9 = 13,275 gallons
💡 Why Knowing Pool Gallons Matters
Accurate volume measurement is crucial for:
- Chemical Treatments: Pool chlorine, shock treatments, algaecide, and pH balancers are all added based on gallons.
- Heater Sizing: Pool heaters are rated by BTUs needed per gallon.
- Pump Efficiency: Water circulation depends on correct flow rates for your pool’s volume.
- Filling Time & Water Bills: Know how much water is needed and how long it’ll take based on your hose flow rate.
🛠️ Additional Tips for Accurate Results
- Measure average depth carefully if your pool has both shallow and deep ends.
Formula: (Shallow Depth + Deep Depth) ÷ 2 - Double-check your pool shape—choosing the wrong one can drastically alter the results.
- Don’t forget steps or attached spas, which also add volume.
- Use a flexible tape measure or a laser measuring device for better accuracy.
❓ 20 Frequently Asked Questions (FAQs)
1. What is a Gallon Pool Calculator?
It’s a tool that estimates how many gallons of water your pool holds based on its shape and dimensions.
2. Why do I need to know how many gallons my pool holds?
To accurately add pool chemicals, manage filtration, and estimate water usage.
3. What shapes does the calculator support?
Rectangular, round, oval, and irregular/freeform shapes.
4. What is the conversion rate from cubic feet to gallons?
1 cubic foot = 7.5 gallons.
5. What is average depth and how do I calculate it?
(Shallow End Depth + Deep End Depth) ÷ 2
6. Can I use this for in-ground and above-ground pools?
Yes, the calculator works for both types.
7. Do steps and spa areas count in the volume?
Yes, include them if you want the most accurate result.
8. Can I calculate gallons for a kidney-shaped pool?
Use the irregular pool option and approximate the surface area.
9. Is the result 100% accurate?
It provides an estimate; exact figures may vary slightly based on pool design.
10. Does the calculator work in metric units?
The tool uses feet and inches. Convert metric values to feet before inputting.
11. What’s the best time to measure pool dimensions?
During daylight with minimal surface disturbance for accuracy.
12. Can I save the results for future use?
Yes, you can note them down or bookmark the result page if supported.
13. Does pool liner thickness affect gallon count?
Not significantly, unless you’re looking for hyper-precise volume.
14. How much water evaporates from a pool daily?
Typically ¼ to ½ inch per day, depending on weather and pool cover.
15. What if my pool has a slope instead of two depths?
Still calculate average depth using measurements from the shallowest and deepest points.
16. Is this calculator mobile-friendly?
Yes, it works well on smartphones, tablets, and desktops.
17. Can I use this for hot tubs or plunge pools?
Yes, for small pools or spas just use appropriate dimensions.
18. How often should I recalculate the volume?
Only if the pool is modified—shape, depth, or added features.
19. How do I calculate pool fill time?
Divide total gallons by your hose’s gallons-per-minute (GPM) flow rate.
20. Can I estimate cost to fill my pool using this?
Yes! Multiply gallons by your municipal water rate to estimate total cost.
🏁 Conclusion
The Gallon Pool Calculator is a must-have tool for every pool owner, helping ensure optimal water quality, efficient maintenance, and better budget management. By inputting just a few basic measurements, you can instantly determine how many gallons of water your pool holds—saving time, money, and guesswork.