Pond Calculator
Calculate pond volume in gallons and the liner size you need, including depth and anchor overlap.
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What this tool does
The Pond Calculator gives water volume in gallons for pump and filter sizing, and works out the flat liner size using the pond-builder's rule: dimension + twice the depth + anchor overlap on each side.
How to use the Pond Calculator
- Enter the pond's surface length and width (or diameter).
- Enter the average depth — ponds with shelves average shallower than the deepest point.
- Keep at least 1 ft of overlap per side for anchoring under edging.
- Buy the liner size shown, rounded up to a stock size.
Formula
Gallons = Surface area × Avg depth × 7.48052; Liner = (L + 2D + 2·overlap) × (W + 2D + 2·overlap)
- 7.48052
- US gallons per cubic foot
- 2D
- Liner climbs down and back up both walls
Worked example
A 10 × 8 ft pond averaging 2.5 ft deep: about 1,496 gallons and a 17 × 15 ft liner.
Inputs
- Pond shapeRectangle / oval (use length × width)
- Length / diameter10 ft
- Width8 ft
- Average depth2.5 ft
- Liner anchor overlap each side1 ft
Result
- Pond volume1,496.1 US gal
- Liner size to buy17 × 15 ft
- Liner area255 sq ft
- Water volume200 cu ft
- Surface area80 sq ft
Results explained
- Pond volume
- Gallons, for pump, filter and treatment dosing.
- Liner size
- Flat liner dimensions before trimming, rounded up.
- Liner area
- Square feet of liner material.
- Water volume (cu ft)
- Cubic feet of water.
Frequently asked questions
Length + (2 × depth) + (2 × overlap). A 10 ft long, 2.5 ft deep pond with 1 ft overlap needs 10 + 5 + 2 = 17 ft of liner length. Same rule for width.
Surface area × average depth × 7.48. A 10 × 8 ft pond at 2.5 ft average depth is about 1,500 gallons — use average, not maximum, depth or you'll oversize everything.
Circulate the full volume at least once every 1–2 hours for a fish pond: a 1,500 gal pond wants a pump rated around 750–1,500 gph at its actual head height.
The extra foot on each side anchors under rocks or edging so the liner can't slip into the pond, and leaves trimming room after the pond settles and fills.
Average. Most garden ponds have plant shelves at 9–12 in and a deep zone; averaging the zones (weight by their area) is far more accurate than the deepest point.