How do I calculate the size of pond liner I need?

The standard formula is: liner length = pond length + (2 x maximum depth) + (2 x edge overlap). The same formula applies to the width. The depth allowance ensures the liner covers the full vertical sides, and the overlap (typically 30cm) secures the liner at the edges under paving or turf. This calculator handles the maths for you instantly.

What is the difference between PVC and butyl pond liner?

PVC liners cost around 5 GBP per square metre and last 10 to 15 years. They are lighter, easier to handle, and adequate for most garden ponds. Butyl rubber liners cost around 12 GBP per square metre but are far more durable, lasting 30 to 50 years. Butyl is more flexible in cold weather, more UV-resistant, and the preferred choice for larger or permanent ponds. Both should be laid over an underlay to protect against stones.

How much overlap should I leave around the pond edge?

A minimum of 30cm (0.3m) overlap is recommended around all edges. This gives enough material to secure the liner under edging stones, slabs, or turf. For larger or deeper ponds, or if using heavy edging, allow 50cm overlap for extra security. The overlap prevents the liner from slipping into the pond as the water weight pulls it down.

Do I need an underlay beneath my pond liner?

Yes, an underlay is strongly recommended. It protects the liner from sharp stones, roots, and other objects in the ground that could cause punctures over time. Geotextile underlay is the most common choice and should be the same dimensions as your liner. Some budget options include old carpet or layers of sand, though purpose-made geotextile is more reliable.

Pond Liner Calculator

Calculate liner dimensions, area, and estimated cost for your garden pond

Published by UltraCalculatorsLast reviewed: 29 Mar 2026v1.0Sources:RHS: Garden ponds Bradshaws DirectReport an issue

Building a garden pond is one of the most rewarding landscaping projects you can take on, and getting the liner size right is a critical first step. Buy too small and you will struggle to achieve the depth you want; buy too large and you waste money on material that gets trimmed away. A pond liner needs to cover not just the surface area but the full depth of the sides, plus an overlap at the edges to anchor it securely. This calculator takes the guesswork out of liner sizing by computing the exact dimensions you need. Simply enter your pond length, width, maximum depth, and desired edge overlap, and the calculator works out the liner length, width, and total area. It also provides cost estimates for both budget PVC liners (around 5 GBP per square metre) and premium butyl rubber liners (around 12 GBP per square metre). Both PVC and butyl liners should be laid over a protective underlay (geotextile fabric) of the same dimensions to prevent punctures from stones and roots in the soil beneath.

How to Use This Calculator

To calculate your pond liner size: 1. Enter the pond length in metres. This is the longest dimension of the hole you plan to dig (or have already dug). 2. Enter the pond width in metres. This is the widest dimension perpendicular to the length. 3. Enter the maximum depth in metres. Use the deepest point, not the average. The liner must reach from the top edge all the way down to the bottom on both sides. 4. Set the edge overlap in metres. The default of 0.3 m (30 cm) is suitable for most ponds. Use 0.5 m for larger ponds or where you plan to lay heavy edging stones. 5. Review the results showing liner length, liner width, total area, and estimated costs for PVC and butyl rubber options.

How It Works

The pond liner calculator uses the standard industry formula: Liner Length = Pond Length + (2 x Maximum Depth) + (2 x Edge Overlap) Liner Width = Pond Width + (2 x Maximum Depth) + (2 x Edge Overlap) The depth is doubled because the liner must go down one side, across the bottom, and back up the other side. The overlap is also doubled to cover both edges. Liner Area = Liner Length x Liner Width This gives the total square metres of liner material needed. Cost estimates: - PVC liner: Area x 5 GBP/m2 (budget option, 10-15 year lifespan) - Butyl rubber liner: Area x 12 GBP/m2 (premium option, 30-50 year lifespan) These prices are approximate UK averages and may vary depending on the supplier, thickness, and any special features such as UV resistance or reinforcement.

Worked Examples

Example 1: Standard garden pond

Inputs: Pond length: 3 m. Pond width: 2 m. Maximum depth: 0.8 m. Edge overlap: 0.3 m.

Liner length = 3 + (2 x 0.8) + (2 x 0.3) = 3 + 1.6 + 0.6 = 5.2 m.
Liner width = 2 + (2 x 0.8) + (2 x 0.3) = 2 + 1.6 + 0.6 = 4.2 m.
Liner area = 5.2 x 4.2 = 21.84 m2.
PVC cost = 21.84 x 5 = 109 GBP.
Butyl cost = 21.84 x 12 = 262 GBP.

Result: You need a liner of at least 5.2 m x 4.2 m (21.84 m2). Budget PVC would cost around 109 GBP, while premium butyl rubber would cost around 262 GBP.

Example 2: Large ornamental pond

Inputs: Pond length: 5 m. Pond width: 4 m. Maximum depth: 1.2 m. Edge overlap: 0.5 m.

Liner length = 5 + (2 x 1.2) + (2 x 0.5) = 5 + 2.4 + 1.0 = 8.4 m.
Liner width = 4 + (2 x 1.2) + (2 x 0.5) = 4 + 2.4 + 1.0 = 7.4 m.
Liner area = 8.4 x 7.4 = 62.16 m2.
PVC cost = 62.16 x 5 = 311 GBP.
Butyl cost = 62.16 x 12 = 746 GBP.

Result: You need a liner of 8.4 m x 7.4 m (62.16 m2). At this size, butyl rubber is the recommended choice for longevity despite the higher upfront cost of approximately 746 GBP.

Example 3: Small wildlife pond

Inputs: Pond length: 1 m. Pond width: 1 m. Maximum depth: 0.5 m. Edge overlap: 0.3 m.

Liner length = 1 + (2 x 0.5) + (2 x 0.3) = 1 + 1.0 + 0.6 = 2.6 m.
Liner width = 1 + (2 x 0.5) + (2 x 0.3) = 1 + 1.0 + 0.6 = 2.6 m.
Liner area = 2.6 x 2.6 = 6.76 m2.
PVC cost = 6.76 x 5 = 34 GBP.
Butyl cost = 6.76 x 12 = 81 GBP.

Result: A small 1m x 1m wildlife pond needs just a 2.6 m x 2.6 m liner (6.76 m2). PVC at around 34 GBP is perfectly adequate for a pond this size.

Frequently Asked Questions

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How to Use This Calculator

How It Works

Worked Examples

Example 1: Standard garden pond

Inputs: Pond length: 3 m. Pond width: 2 m. Maximum depth: 0.8 m. Edge overlap: 0.3 m.

Liner length = 3 + (2 x 0.8) + (2 x 0.3) = 3 + 1.6 + 0.6 = 5.2 m.
Liner width = 2 + (2 x 0.8) + (2 x 0.3) = 2 + 1.6 + 0.6 = 4.2 m.
Liner area = 5.2 x 4.2 = 21.84 m2.
PVC cost = 21.84 x 5 = 109 GBP.
Butyl cost = 21.84 x 12 = 262 GBP.

Result: You need a liner of at least 5.2 m x 4.2 m (21.84 m2). Budget PVC would cost around 109 GBP, while premium butyl rubber would cost around 262 GBP.

Example 2: Large ornamental pond

Inputs: Pond length: 5 m. Pond width: 4 m. Maximum depth: 1.2 m. Edge overlap: 0.5 m.

Liner length = 5 + (2 x 1.2) + (2 x 0.5) = 5 + 2.4 + 1.0 = 8.4 m.
Liner width = 4 + (2 x 1.2) + (2 x 0.5) = 4 + 2.4 + 1.0 = 7.4 m.
Liner area = 8.4 x 7.4 = 62.16 m2.
PVC cost = 62.16 x 5 = 311 GBP.
Butyl cost = 62.16 x 12 = 746 GBP.

Result: You need a liner of 8.4 m x 7.4 m (62.16 m2). At this size, butyl rubber is the recommended choice for longevity despite the higher upfront cost of approximately 746 GBP.

Example 3: Small wildlife pond

Inputs: Pond length: 1 m. Pond width: 1 m. Maximum depth: 0.5 m. Edge overlap: 0.3 m.

Liner length = 1 + (2 x 0.5) + (2 x 0.3) = 1 + 1.0 + 0.6 = 2.6 m.
Liner width = 1 + (2 x 0.5) + (2 x 0.3) = 1 + 1.0 + 0.6 = 2.6 m.
Liner area = 2.6 x 2.6 = 6.76 m2.
PVC cost = 6.76 x 5 = 34 GBP.
Butyl cost = 6.76 x 12 = 81 GBP.

Result: A small 1m x 1m wildlife pond needs just a 2.6 m x 2.6 m liner (6.76 m2). PVC at around 34 GBP is perfectly adequate for a pond this size.