---
title: "Pond Liner Calculator: What Size Liner? | Pond Mosaic"
description: "How much pond liner do you need? Length + 2 × depth + overlap, for any shape, in metres and feet, with underlay, stock sizes and a to-scale drawing."
url: https://pondmosaic.me/
---

Metres and feet, side by side

# Pond liner calculator

How much pond liner do you need? **Length + 2 × deepest depth + 2 × overlap**, and the same for the width. Enter your pond below for the liner and underlay size, the nearest stock sizes and a to-scale drawing.

## More pond tools

- [Pond liner calculator](https://pondmosaic.me/): Liner and underlay size for any shape, with stock sizes.
- [Pond volume calculator](https://pondmosaic.me/pond-volume-calculator/): Litres, US and UK gallons, water weight and fill time.
- [Pond pump calculator](https://pondmosaic.me/pond-pump-calculator/): Flow for your pond, head height, waterfalls and running cost.
- [Fish stocking calculator](https://pondmosaic.me/fish-stocking-calculator/): How many fish, from named sources, and feeding by temperature.
- [Wildlife pond planner](https://pondmosaic.me/wildlife-pond-planner/): A printable build and planting checklist for your garden.
- [Pond plant depth guide](https://pondmosaic.me/pond-plant-depth-guide/): Planting depths by RHS zone, native status and flowering.
- [Winter pond care](https://pondmosaic.me/winter-pond-care/): Ice, leaf nets, pumps and a month-by-month calendar.

## Autumn and winter at the pond

Net ponds against falling leaves in autumn, stop feeding fish once cold weather sets in, and never smash ice: melt a hole with a pan of hot water instead. Winter is also a good time to dig a wildlife pond, so autumn and winter rain can fill it ready for spring. [Winter pond care](https://pondmosaic.me/winter-pond-care/) · [Plan a wildlife pond](https://pondmosaic.me/wildlife-pond-planner/)

## Recommended

### CleanTempMail

Pond and wildlife guides, planting packs and supplier price lists are often sent only to an email address. CleanTempMail gives you a free temporary inbox, with no sign-up, that receives the link and deletes everything after three days, so the follow-up newsletters never reach your real inbox.

[Get a temporary inbox](https://cleantempmail.com/)

### WebTraceCheck

Found a liner or pump at a price that looks too good, on a shop you've never heard of? WebTraceCheck's free domain lookup shows how old a shop's website is, and its disposable cloud browser lets you open an unfamiliar link on an isolated desktop that is deleted after the session.

[Check a shop first](https://webtracecheck.com/)

## How much pond liner do I need?

A flexible liner has to run down both sides of the hole, across the floor and over the edge on both sides. So for each direction:

Liner length = longest length + 2 × deepest depth + 2 × overlap

The width works the same way with the widest width. For a 3 × 2 m pond, 0.6 m deep, with 30 cm of overlap: 3 + 1.2 + 0.6 = 4.8 m by 2 + 1.2 + 0.6 = 3.8 m.

- **Circle:** use the diameter for both length and width. **Oval or irregular:** measure the longest length and the widest width, at right angles to each other.
- **Overlap:** the RHS suggests about 15 cm (6 in) all round; Firestone adds 2 ft to each dimension, a foot on each side; Bradshaws allows 50 cm. More overlap is easier to anchor under paving or turf.
- **Shelves** don't change the sum. Going down to a shelf, across it and down again uses no more liner than a straight side to the full depth, so the deepest depth covers it.
- **Underlay** is sized the same way: buy the same length and width as the liner.

## Sources

1. Firestone Building Products, [PondGard EPDM pond liner brochure](https://cdn.shopify.com/s/files/1/1583/4445/files/pondgard-brochure.pdf) (item 1947, 2014): “How to calculate quantity of liner”, width plus 2 × depth plus 2 extra feet, and the standard roll widths of 10, 15, 20, 25, 30, 40 and 50 ft.
2. Freshwater Habitats Trust, Amphibian and Reptile Conservation and World of Water, [Creating Garden Ponds for Wildlife](https://freshwaterhabitats.b-cdn.net/app/uploads/2023/06/Creating-Garden-Ponds_2023.pdf) (2023): (length + 2 depths + 30 cm) by (width + 2 depths + 30 cm).
3. RHS, [How to make a new pond](https://www.rhs.org.uk/ponds/construction-and-repair): the liner should overlap the edge by about 15 cm (6 in) all round.
4. Bradshaws, [How much pond liner do I need?](https://bradshawsdirect.co.uk/blog/planning-a-pond-how-much-pond-liner-do-i-need) (21 November 2019): length + 2 × depth + 1 m, an overlap of 50 cm on each side; underlay = the liner's length × width.
5. Webb's Water Gardens, [How to size a pond liner](https://webbsonline.com/Article/how-to-measure-pond-liner) (20 February 2024): length + 2 × depth + 2 ft, a foot each side; the same square footage of underlay as liner.
6. Exact conversions: 1 ft = 0.3048 m ([NIST Handbook 44, Appendix C](https://www.nist.gov/document/2026-nist-handbook-44-appendix-c); [Weights and Measures Act 1985, Schedule 1](https://www.legislation.gov.uk/ukpga/1985/72/schedule/1)).

The stock sizes in the calculator are examples to show how the comparison works, not any supplier's range: replace them with your supplier's sizes.

## Pond liner questions

**How do I work out pond liner size?**

Add twice the deepest depth and twice the overlap to the pond's longest length, then do the same with its widest width. A 3 × 2 m pond, 0.6 m deep, with 30 cm overlap needs a 4.8 × 3.8 m liner.

**How much overlap should a pond liner have?**

The RHS suggests about 15 cm (6 in) all round. Liner makers and sellers often allow more: Firestone adds a foot on each side, and Bradshaws 50 cm, which gives more to tuck under edging.

**Do marginal shelves need extra liner?**

No. The liner follows the steps down, but the total is never more than a straight drop to the deepest point, so sizing from the maximum depth already covers shelves.

**What size underlay do I need?**

The same size as the liner. Underlay goes under the whole liner, up the sides and under the overlap, so buy the same length and width, or the same area.