Pond Liner Calculator

Size a flexible pond liner from maximum length, width and depth plus edge overlap, with liner area, optional underlay cost and an approximate water volume.

Interactive calculator · Method POND-LINER-1.0 · Last reviewed: 2026-11-04

Calculate your scenario

Liner length = pond length + 2 × max depth + 2 × edge overlap; liner width = pond width + 2 × max depth + 2 × overlap.

Your inputs

Try an example

Pond maximum length (ft)

Pond maximum width (ft)

Pond maximum depth (ft)

Edge overlap on each side (ft)

Volume shape factor (editable assumption, example 0.85 for sloped sides) (× box volume)

Liner price per sq ft (example) ($ per sq ft)

Underlay price per sq ft (example; 0 to skip) ($ per sq ft)

Default worked example. Edit the inputs to calculate your scenario.

Default worked example

Liner length 16 ft

Liner width 14 ft

Liner area 224 sq ft (20.81 m²)

Approximate water volume 1,017.35 US gal (3,851.09 L)

Liner and underlay cost $291.20

Liner = (10 + 2 × 2 + 2 × 1) × (8 + 2 × 2 + 2 × 1) = 16 × 14 ft = 224 sq ft.

How to use the calculator

Measure the longest length, widest width and deepest point of the dug hole (or planned pond), choose how much liner should lie flat beyond the edge on each side, and adjust the shape factor if your sides are steeper (closer to 1) or more sloped (lower).

What the result means

A 10 × 8 ft pond 2 ft deep with 1 ft overlap needs a 16 × 14 ft liner (224 sq ft) and holds roughly 1,017 gallons at a 0.85 shape factor; liner and underlay come to $291.20 at the example prices.

Formula and units

Liner length = pond length + 2 × max depth + 2 × edge overlap; liner width = pond width + 2 × max depth + 2 × overlap. Liner area = length × width. Approximate volume = length × width × depth × shape factor, in ft³, × 1,728 ÷ 231 for US gallons (× 28.3168 for liters). Cost = liner area × (liner price + underlay price).

Worked examples

10 × 8 ft pond, 2 ft deep, 1 ft overlap: Pond maximum length: 10 ft; Pond maximum width: 8 ft; Pond maximum depth: 2 ft; Edge overlap on each side: 1 ft; Volume shape factor (editable assumption, example 0.85 for sloped sides): 0.85 × box volume; Liner price per sq ft (example): 1 $ per sq ft; Underlay price per sq ft (example; 0 to skip): 0.3 $ per sq ft.
Example result: Liner length: 16 ft; Liner width: 14 ft; Liner area: 224 sq ft (20.81 m²); Approximate water volume: 1,017.35 US gal (3,851.09 L); Liner and underlay cost: $291.20.

15 × 10 ft pond, 3 ft deep, 1.5 ft overlap, no underlay: Pond maximum length: 15 ft; Pond maximum width: 10 ft; Pond maximum depth: 3 ft; Edge overlap on each side: 1.5 ft; Volume shape factor (editable assumption, example 0.85 for sloped sides): 0.7 × box volume; Liner price per sq ft (example): 1.25 $ per sq ft; Underlay price per sq ft (example; 0 to skip): 0 $ per sq ft.
Example result: Liner length: 24 ft; Liner width: 19 ft; Liner area: 456 sq ft (42.36 m²); Approximate water volume: 2,356.36 US gal (8,919.81 L); Liner and underlay cost: $570.00.

Limitations and common mistakes

Uses the maximum length, width and depth, so the liner covers shelves and slopes with some spare; very irregular ponds may need more. The shape factor is an editable assumption for sloped sides and shelves, not a measured volume. Liners are sold in fixed sizes, so round up to the next available size. This sizes material only; it says nothing about whether the pond will hold water, liner suitability for fish or plants, or installation.

Using the average depth for the liner. The liner must reach the deepest point and come back up, so it uses the maximum depth twice in each direction.

Sources and assumptions

Method POND-LINER-1.0; last formula review 2026-11-04. Sources and their supported claims. Calculation methodology.