Pond Volume Calculator
Find out how many gallons your pond holds, whether it's a backyard koi pond or a multi-acre lake. Choose your pond's shape, enter its size and average depth, and get the volume instantly.
Next steps: size a pond pump, an aeration system, or dose pond treatments using your gallons. Questions? Call 888-825-6214.
How to calculate pond volume
Pond volume is surface area multiplied by average depth, which gives cubic feet. Multiply cubic feet by 7.48 to convert to gallons. The only thing that changes from shape to shape is how you find the surface area.
Rectangular or square ponds
Example: a 12' × 8' pond with an average depth of 3' holds 12 × 8 × 3 = 288 cubic feet, or about 2,154 gallons.
Round ponds
The radius is half the diameter. Example: a round pond 10' across and 2' deep on average holds 3.14 × 5 × 5 × 2 = 157 cubic feet, or about 1,175 gallons.
Oval ponds
Irregular ponds
Most backyard ponds aren't a perfect shape. Measure the length and width in several places, average each set, and use the rectangular formula with those averages. If your pond is clearly made of separate sections, calculate each section on its own and add them together.
Large ponds and lakes measured in acres
One acre-foot (one acre of surface, one foot deep) is about 325,851 gallons. A 1-acre pond with a 6' average depth holds roughly 6 acre-feet, or about 1.96 million gallons.
How to find your pond's average depth
Average depth matters more than any other number in the calculation, and it's the one most people get wrong. Using the deepest point will overstate your volume, sometimes by a lot, because most ponds slope from shallow edges down to a deeper center.
To estimate it, take depth readings at evenly spaced points across the pond with a weighted line or a marked pole, including spots near the edges, then average them. The more readings you take, the closer your estimate will be. For large ponds, readings taken from a boat along a few straight lines across the water work well.
Why your pond's volume matters
- Pump sizing: Pumps are rated in gallons per hour (GPH). A common rule of thumb for fish ponds and water gardens is to circulate the full volume at least once every one to two hours. Compare pond pumps at the height you need to push water, since flow drops as height increases.
- Treatment dosing: Algaecides, bacteria, dyes, and other pond treatments are dosed by gallons or acre-feet. Overdosing wastes money and can harm fish, while underdosing doesn't work.
- Aeration: Aeration systems are matched to surface area and depth. Knowing your volume helps you confirm you're choosing the right size.
- Building a new pond? Our pond liner size calculator tells you what size liner you'll need, and our koi pond kits bundle the main components in one order.
Frequently asked questions
How many gallons are in a cubic foot of water?
One cubic foot holds about 7.48 gallons of water.
How many gallons are in an acre-foot?
About 325,851 gallons. An acre-foot is one acre of surface area covered one foot deep.
How accurate is this calculator?
The math is exact for the measurements you enter, so accuracy depends on your measurements, especially average depth. For irregular ponds and natural ponds with sloped banks, treat the result as a close estimate.
Should I use maximum depth or average depth?
Average depth. Most ponds are shallow at the edges and deeper in the middle, so using the deepest point overstates the volume.
How do I convert gallons to liters?
Multiply gallons by 3.785. The calculator shows liters automatically.
