Pond Gallon Calculator
Find out how many gallons your pond holds in seconds. This pond gallon calculator takes pond length, width, and average depth, then returns the exact gallons for US and UK imperial units, plus cubic feet and liters for cross-checking. Works for rectangular ponds, round ponds, oval ponds, and irregular natural ponds where you already know the surface area. Getting gallons right is the starting point for every pond medication, dechlorinator, and fish stocking decision.
Gallon Calculator Pond Formula
Pond gallons equals surface area (sq ft) times average depth (ft) times 7.48 gallons per cubic foot:
- Rectangular: Length x Width x Avg Depth x 7.48 = gallons
- Round: pi x Radius^2 x Avg Depth x 7.48
- Oval: pi x (Length/2) x (Width/2) x Avg Depth x 7.48
- Irregular: Measured Surface Area (sq ft) x Avg Depth x 7.48
Gallons In Pond Calculator Reference
A gallons in pond calculator is most useful when you pair it with a quick reference for common pond sizes. Here are typical backyard pond gallons:
| Pond Size | Shape | Avg Depth | Gallons |
|---|---|---|---|
| 6 x 4 ft | Rectangular | 1.5 ft | 270 gal |
| 8 x 5 ft | Rectangular | 2 ft | 600 gal |
| 10 x 6 ft | Rectangular | 2.5 ft | 1,120 gal |
| 12 x 8 ft | Rectangular | 3 ft | 2,155 gal |
| 6 ft diameter | Round | 2 ft | 423 gal |
| 8 ft diameter | Round | 2 ft | 752 gal |
| 10 ft diameter | Round | 2.5 ft | 1,469 gal |
| 16 x 20 ft | Rectangular | 4 ft | 9,575 gal |
How to Use the Pond Gallon Calculator
- Pick your pond shape from the dropdown.
- Measure length and width in feet at the water line (not the liner edge).
- Measure shallow and deep depth; enter (shallow + deep) / 2 as average depth.
- For irregular ponds, trace the outline on Google Earth's measure tool to get surface area in sq ft, then pick Irregular.
The pond gallon calculator rounds to the nearest whole gallon. For medication and treatment dosing, always round up to the nearest 100 gallons to stay safe.
Why Pond Gallons Matter
Every pond treatment on the market is dosed per 1,000 gallons. Dechlorinator, anti-parasite, anti-fungal, algaecide, pond salt, and sludge remover all key off gallons. Pumps are sized to turn over the full gallon count every 1-2 hours for koi ponds, every 2-4 hours for goldfish ponds. Filters are rated by maximum pond gallons they can support. A 10% error in gallons means a 10% error in every pond product you add, which over a season adds up to real money and dead fish.
Fish Stocking from Pond Gallons
The classic ornamental pond rule is 1 inch of fish body length per 10 gallons of water with moderate filtration. A 1,500 gallon pond supports about 150 inches of fish, which is roughly 10 koi at 15 inches each, or 30 goldfish at 5 inches each. Heavily filtered and aerated ponds can stock 1 inch per 5 gallons; new or unheated ponds should stay below 1 inch per 20 gallons. For bass/bluegill farm ponds, stocking is measured per surface acre instead (100 bass + 500 bluegill per acre).
Pond Gallon Calculator vs Literage Calculator
If you prefer metric, use our Pond Literage Calculator, which returns volume in litres and cubic metres from the same inputs. US and Canadian pond keeping literature uses gallons; European, UK, and Australian literature uses litres. 1 US gallon = 3.785 litres, so a 1,500 US gallon pond equals about 5,678 litres.