What is the formula for pond liner size?

The standard UK formula is: Liner Length = Max Length + (2 x Max Depth) + (2 x Overlap). Liner Width = Max Width + (2 x Max Depth) + (2 x Overlap). A standard overlap is 0.5 metres.

Do I really need pond underlay?

Yes. Even if your soil seems soft, stones and roots can move over time and puncture your liner. Underlay is a cheap insurance policy that significantly extends the life of your pond.

Which material is best for a pond liner?

EPDM (Butyl) rubber is the best choice for most UK ponds. It is flexible, UV-resistant, and can last over 20 years. PVC is a cheaper alternative for smaller, shallower ponds.

How deep should a fish pond be in the UK?

For goldfish, a minimum depth of 45-60cm is recommended. For Koi, you should aim for at least 1 metre to ensure the water temperature remains stable and to prevent the pond from freezing solid in winter.

What is the formula for pond liner size?

The standard UK formula is: Liner Length = Max Length + (2 x Max Depth) + (2 x Overlap). Liner Width = Max Width + (2 x Max Depth) + (2 x Overlap). A standard overlap is 0.5 metres.

Do I really need pond underlay?

Yes. Even if your soil seems soft, stones and roots can move over time and puncture your liner. Underlay is a cheap insurance policy that significantly extends the life of your pond.

Which material is best for a pond liner?

EPDM (Butyl) rubber is the best choice for most UK ponds. It is flexible, UV-resistant, and can last over 20 years. PVC is a cheaper alternative for smaller, shallower ponds.

How deep should a fish pond be in the UK?

For goldfish, a minimum depth of 45-60cm is recommended. For Koi, you should aim for at least 1 metre to ensure the water temperature remains stable and to prevent the pond from freezing solid in winter.

Pond Liner Estimator

Calculate liner dimensions and water volume for your garden pond.

Max Length (m)

Max Width (m)

Max Depth (m)

Edge Overlap (m)

* Most UK pond suppliers recommend a minimum overlap of 0.5m to allow for anchoring with stones or timber.

Liner Size Needed

Selection Tip: For small garden ponds, a **0.5mm PVC** liner is sufficient. For larger ponds or those containing Koi, a **0.75mm or 1mm EPDM** rubber liner is highly recommended for durability and puncture resistance.

UK Garden Pond Design Guide

Wildlife Haven

A garden pond is one of the best ways to attract wildlife and create a tranquil focal point in your outdoor space. Whether it's a small pre-formed pool or a large custom-dug Koi pond, getting the liner size right is the first step.

Using our **pond liner calculator** ensures you don't end up with a liner that's too small, which is a common and costly mistake that usually requires starting the project from scratch.

Volume Converter

1 Cubic Metre1,000 Litres

1 Litre0.22 Gallons (UK)

1 Gallon (UK)4.546 Litres

Material Choices

PVC

Budget-friendly, 10-year life. Best for small ponds.

EPDM

Pro choice, 20+ year life. High flexibility.

Underlay

Mandatory. Geotextile fabric to prevent punctures.

Pro Tip: The String Method

For irregular-shaped ponds, use a long piece of string. Lay it across the longest part of the hole, following all the contours of the base and sides. Measure the string, add your overlap, and that's your minimum liner length. Repeat for the width.

Garden Pond FAQ

Excavation Safety

Always check for underground cables and pipes (gas, water, electric) before you start digging. In the UK, you can use the 'Dial Before You Dig' services or hire a CAT scanner to be safe.