How this calculator works
It adds twice the maximum depth (so the liner can run down one side and up the other) plus an overlap allowance on every edge to the pond’s length and width. Pond volume uses length × width × depth × 0.7 (a shape factor for sloped sides) × 7.48 gallons per cubic foot.
Worked example — a 10 ft × 8 ft pond, 2 ft deep, with a 1 ft overlap on each side:
Length: 10 + (2 × 2) + (2 × 1) = 16 ft; width: 8 + 4 + 2 = 14 ft → 224 sq ft. Round up to the standard 20 × 15 ft liner. Volume: 10 × 8 × 2 × 0.7 × 7.48 ≈ 838 gallons.
Length: 10 + (2 × 2) + (2 × 1) = 16 ft; width: 8 + 4 + 2 = 14 ft → 224 sq ft. Round up to the standard 20 × 15 ft liner. Volume: 10 × 8 × 2 × 0.7 × 7.48 ≈ 838 gallons.
Measure the maximum depth, not the average
Use the deepest point of the pond, including any shelves you dig, and the longest and widest dimensions. Liners are sold in standard sizes (usually 5 ft increments), so round up rather than down.
Frequently asked questions
How much overlap should a pond liner have?
Plan on 1–2 feet of overlap on every side so the edge can be tucked under rocks or coping and sit above the waterline.
How do I figure out how many gallons my pond holds?
Multiply length × width × average depth in feet, then by 7.48. For irregular ponds with sloped sides, multiply by about 0.7 first for a realistic estimate.