Setup & Sizing
Pond Liner Calculator
Work out exactly what size pond liner you need. The calculator automatically allows for the depth of the pond and a safety overlap around every edge.
Pond Liner Calculator
Deepest point, not the average.
30 cm (0.3 m / 1 ft) is the usual minimum.
Liner dimensions needed
5.2 x 4.2m
- Liner length (m)
- 5.2
- Liner width (m)
- 4.2
- Surface area (m²)
- 21.84
How pond liner size is worked out
A flat liner has to drape down one side of the pond, across the bottom, up the opposite side, and overlap at both edges. So both the liner length and width need double the pond depth plus double the edge overlap.
Formulas:
- Liner length = pond length + (2 x depth) + (2 x overlap)
- Liner width = pond width + (2 x depth) + (2 x overlap)
Worked example
A pond that is 3 m x 2 m and 0.8 m deep, with a 30 cm (0.3 m) overlap on each side, needs a liner of 3 + (2 x 0.8) + (2 x 0.3) = 5.2 m by 2 + (2 x 0.8) + (2 x 0.3) = 4.2 m. Round up to the next stock size (usually 6 m x 5 m) to avoid cutting it too fine, and trim off the excess once the pond is filled and settled.
Buying tips
Always order the liner to arrive before you dig - it lets you test-fit and fold it on the lawn first. If you're edging with slate or stone, allow a little more overlap (40-50 cm) so you can tuck the liner under a generous stone lip.
Frequently asked questions
Why add an overlap to the liner?
An overlap lets the liner fold over the edge of the pond so it can be hidden under rocks, stones or turf. It also gives you a tolerance for irregular sides - no garden pond is dug perfectly square. UK pond suppliers almost always recommend a minimum 30 cm (1 ft) overlap on every side.
What are the standard liner size increments?
Liners are usually sold in set widths (2m, 3m, 4m, 5m, 6m, 7m and 8m) cut to the length you need. If your calculated size falls between two stock widths, always round up to the next full size rather than trim a smaller liner thin.
Should I pick butyl (EPDM), PVC or LDPE?
For most UK garden ponds, EPDM butyl rubber is the go-to: a 25+ year lifespan, fish-safe and flexible enough to fit most shapes. PVC is cheaper but shorter-lived (10-15 years) and stiffens up in cold winters. LDPE is the cheapest and thinnest, best for wildlife ponds with gentle, shallow sides.
What if my pond has shelves or a deep sump?
The formula already covers most shelf configurations because the deepest point drives the numbers. If you have an unusually deep sump (for a bottom drain, for example), add 2 x (sump depth) to both the length and width before ordering.