How Many Gallons Is My Pond? Liner Size and Pump Flow
Part of the project planner: Planning pools, ponds and water storage.
An oval pond 10 × 6 ft with an average depth of 2 ft holds about 705 gallons. It needs an 18 × 14 ft liner if the deepest point is 3 ft, and a pump that moves about 705 gallons an hour. The chart covers other sizes, and the page explains the shapes.
Gallons, liner and pump for common ponds
Oval ponds with an average depth of 2 ft and a deepest point of 3 ft, with the pump flow for one turnover an hour:
| Pond | Gallons | Liner | Pump (GPH) | Weight of water |
|---|---|---|---|---|
| 6 × 4 ft | 282 | 14 × 12 ft | 282 | 2,352 lb |
| 8 × 5 ft | 470 | 16 × 13 ft | 470 | 3,920 lb |
| 10 × 6 ft | 705 | 18 × 14 ft | 705 | 5,880 lb |
| 12 × 8 ft | 1,128 | 20 × 16 ft | 1,128 | 9,408 lb |
| 15 × 10 ft | 1,763 | 23 × 18 ft | 1,763 | 14,701 lb |
| 20 × 12 ft | 2,820 | 28 × 20 ft | 2,820 | 23,521 lb |
How the shape changes the volume
For a pond with a 10 × 6 ft footprint and a 2 ft average depth:
| Shape | Volume |
|---|---|
| Rectangle | 898 gallons |
| Oval or round | 705 gallons |
| Free-form | 628 gallons |
An oval or round pond holds about 79% of a rectangle with the same length and width, and a free-form one about 70%. Use the pond volume calculator for yours.
Sizing the liner
The liner has to cover the floor and rise up each side by the depth, with a margin at the edges: length plus 2 × the deepest point plus 2 ft, by width plus 2 × the deepest point plus 2 ft. Add 10% for a pond with several shelves or steep walls. Buy an underlayment to go under it, and leave slack, so that the liner does not stretch as the pond fills.
Sizing the pump
A pump should move the whole volume through the filter about once an hour for a pond with fish, so a 705 gallon pond needs about 705 GPH. For plants and a few fish, once every two hours is enough, and for a heavy fish load, twice an hour. A pump is rated with no lift, and the flow falls as the water has to rise, so check the maker's curve for the height of your waterfall or filter.
Before you dig
- Call 811 before you dig, so that buried lines are marked.
- Pick the spot. Level ground, away from big tree roots and leaves, with some sun and some shade, is best.
- Check local rules. Some areas require a fence or cover for a pond deeper than a certain depth, because it is a drowning hazard for young children.
- Plan the depth. At least 2 feet over part of it helps fish and plants through the winter in most places. Go deeper in a cold climate.
Mistakes that cost people money
- A liner that is too small, and cannot be stretched to fit.
- Not leveling the rim, so the pond overflows on one side.
- A pump that is too small, which leaves the water green, or too big, which stresses the fish.
- Putting a pond on a deck or roof without checking the load. A 700 gallon pond weighs almost 3 tons.
Frequently asked questions
How do I calculate the gallons in my pond?
Multiply the length by the width by the average depth (all in feet) to get cubic feet, multiply by 0.785 for an oval or 0.7 for a free-form pond, and then by 7.481 to get gallons.
What size liner do I need for my pond?
Length plus twice the deepest point plus 2 feet, by width plus twice the deepest point plus 2 feet. A 10 × 6 ft pond that is 3 ft deep needs an 18 × 14 ft liner.
What size pump do I need for a pond?
Enough to move the pond's volume once an hour: a 705 gallon pond needs a pump of about 705 GPH at the height it lifts the water, and more for a waterfall or heavy fish load.
How much does the water in a pond weigh?
About 8.34 pounds a gallon, so a 705 gallon pond has about 5,880 lb of water: make sure the ground, a deck or a roof can carry it.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.