Pond Volume Calculator
Estimate your pond's volume in gallons from its length, width, and average depth to size a pump, liner, or fish stocking plan.
How this calculator works
Pond volume is length times width times average depth, giving cubic feet — then multiplied by 7.48, the number of gallons in a cubic foot, to get total gallons. This treats the pond as a rectangular basin, which is a starting approximation for the irregular shapes most ponds actually have.
Formula: Gallons = Length (ft) x Width (ft) x Average depth (ft) x 7.48.
Worked example
A 10 ft x 6 ft pond with a 24-inch (2 ft) average depth:
- Average depth in feet: 24 ÷ 12 = 2 ft
- Gallons: 10 x 6 x 2 x 7.48 = 897.60 gallons
- At $0.01/gallon for fill water, that’s $8.98.
Coverage reference
| Pond footprint | Average depth | Gallons |
|---|---|---|
| 6 ft x 4 ft | 1.5 ft | 269 gallons |
| 10 ft x 6 ft | 2 ft | 898 gallons |
| 15 ft x 10 ft | 2.5 ft | 2,805 gallons |
How to measure your pond
Measure the pond’s longest length and widest width at the waterline in feet, then estimate an average depth across its shelves and deep zones. Because most ponds curve and slope rather than form a true rectangle, treat this calculator’s result as an upper-bound estimate — actual volume typically runs 80-90% of the rectangular figure for a naturally shaped pond.
Frequently asked questions
How do I calculate my pond's volume in gallons?
Multiply length x width x average depth (in feet), then multiply by 7.48 gallons per cubic foot. This calculator does that automatically — enter your pond's dimensions and average depth in inches, and it converts everything for you.
My pond isn't a rectangle — how accurate is this?
Most ponds are irregular in shape, not rectangular, so treating it as a rectangle overestimates true volume. As a rule of thumb, estimate an irregular pond at about 80-90% of what the rectangular formula gives you, since curved edges and sloped sides hold less water than a boxy shape of the same footprint.
What is 'average depth' for a pond with shelves or a deep zone?
Add your shallow-marginal-shelf depth and your deepest zone's depth together and divide by 2, the same approach used for a pool with a shallow and deep end. If your pond has multiple depth zones (marginal shelf, mid-zone, deep zone), a weighted average based on how much surface area each zone covers will be more accurate.
What does pond volume tell me that I need to know?
Gallons is the key number for sizing almost everything else: pump and filter flow rate (often sized to turn over the full volume every 1-2 hours), UV clarifier sizing, liner square footage, fish stocking density (koi need roughly 250+ gallons per adult fish), and dosing for algaecide or dechlorinator treatments.
Why is the default price so low ($0.01/gallon)?
That default estimates the cost to fill the pond with municipal water, not the pond's construction cost. Adjust it to your local water rate if you want a fill-cost estimate, or ignore the cost figure entirely if you're just after the gallon count for pump or stocking sizing.
Estimates only. Verify quantities with your supplier before purchasing.