Independent comparisons. We may earn from shop links. More info

How to fit a pond liner

Updated: 22 October 2026

This is how to fit a pond liner once that sheet is chosen: level the rim, cushion the hole, add twice the depth plus an overlap you can name, and keep the scissors away until the pond is full. The twelve sheets in our [pond membrane comparison](/hub/garden-ponds/pond-membrane) do not include fleece. Fish and children sit on the [wildlife pond liner](/hub/garden-ponds/pond-membrane/sub/pond-membrane-wildlife) page, and the cut itself is on the [pond liner buying guide](/hub/garden-ponds/pond-membrane/sub/pond-membrane-buying-guide). Peter F. prepared this on 19 October 2026 from those listings and public UK fitting notes, without a test pond. A qualifying purchase can earn us a commission at no extra cost to you.

This is how to fit a pond liner once that sheet is chosen: level the rim, cushion the hole, add twice the depth plus an overlap you can name, and keep the scissors away until the pond is full.

Our top picks

PondKraft PondKraft pond liner, 3 x 2.5 m

Best overall

PondKraft PondKraft pond liner, 3 x 2.5 m
8.6/10about £14.99
View offer
GARDENIX GARDENIX pond liner, 1 x 1 m, 200 gsm

Rank 2

GARDENIX GARDENIX pond liner, 1 x 1 m, 200 gsm
6.2/10about £6.72
View offer
mawmuaw mawmuaw pond liner, 2 x 2 m, 0.1 mm

Rank 3

mawmuaw mawmuaw pond liner, 2 x 2 m, 0.1 mm
5.0/10about £8.99
View offer
On this page
  1. 1.Mark a level outline
  2. 2.The size sum, with the overlap you chose
  3. 3.What goes under the sheet
  4. 4.Fill, then trim

Mark a level outline

A pond that sits low on one side looks full there and unfinished opposite. The Royal Horticultural Society’s construction notes treat a level rim as part of the build. Set a straight board across the marked outline, run a spirit level along it, then repeat on the other axis before you cut any shelves. If one side of a 1.2 m square sits about 4 cm low, that bank will spill. Stones, roots and rubble come out of the floor while you can still see them, because the cushion hides whatever you leave behind.

The size sum, with the overlap you chose

Newcastle City Council’s wildlife ponds guide sizes the liner as the pond length plus twice the depth, and the same again for the width, before any overlap. On the RSPB example, 1.2 m by 1.2 m at 0.4 m deep becomes 2 m by 2 m. That is the hole, not the finished edge. The published overlaps stay three figures. RHS construction advice is about 15 cm. The RSPB guide is about 30 cm. GARDENIX’s bullets ask for at least 50 cm after the depth is added, and they say not to cut until the pond is full. If the sheet you own is that 2 m square, you have nothing left for even the 15 cm fold.
PondKraft PondKraft pond liner, 3 x 2.5 m

Testsieger

PondKraft PondKraft pond liner, 3 x 2.5 m
8.6/10about £14.99
View offer

What goes under the sheet

The liner is not the cushion. On stony ground the RHS suggests underfelt, or about 2.5 cm of sand. Bradshaws wants sand, then an underlay that will not rot, and argues against old carpet and newspaper. Pondkeeper says fleece should match the liner size, overlap by about 7–10 cm, and cover the rim. None of the twelve boxes includes that fleece. The 16 cm mawmuaw nails are fixings, not a substitute. Keep them in the dry overlap beyond the rim. A nail through the wet floor is a leak you fitted yourself.

Fill, then trim

Leave the scissors until the pond is full and the sheet has stopped moving. GARDENIX and Pondkeeper both say not to cut the pond liner until it is full of water. The Pond People say trim after it has settled, and leave at least 30 cm. Bradshaws says do not edge the pond until it has settled. If one side looks full while the other still shows a dry slope, stop and re-level the rim before you trim. A landscaper should take the job if the outline crosses drains or buried cables, or if the sheet has to be welded. An electric pump stays with a qualified electrician.

Common questions

How do I work out the sheet size?
Add the pond length to twice the depth, and do the same for the width. Newcastle’s wildlife pond notes use that sum for the hole itself. On the RSPB example, 1.2 m by 1.2 m at 0.4 m deep becomes 2 m by 2 m before any overlap. You then add the overlap you have chosen, whether that is about 15 cm, about 30 cm, or at least 50 cm. A sheet ordered to the water surface alone is already short of this sum.
Is 15 cm of overlap enough?
Fifteen centimetres is the RHS figure, and it is the smallest of the three published allowances here. It can be enough on a level rim when that 15 cm is still spare after the twice-depth sum. The RSPB guide uses about 30 cm. GARDENIX asks for at least 50 cm after the depth has been added to both sides. Pick one figure and buy to it, rather than averaging them into a number nobody published.
Do any of these twelve include fleece?
No. Fleece is a separate purchase for every listing in the comparison. Pondkeeper’s underlay advice is to buy it to the same size as the liner, overlap the pieces by about 7–10 cm, and carry it over the rim. Old carpet and newspaper sit beside that advice as materials Bradshaws treats as underlay that rots. About 2.5 cm of sand is the RHS option where the ground is stony and you are laying a mineral layer rather than fleece alone.
Can I use the mawmuaw nails in the bottom?
No. The mawmuaw nails are 16 cm long, and they are fixings for the dry ground beyond the water, not a cushion under the sheet. A nail through the liner on the pond floor is a leak. If you use them, keep them in the overlap outside the rim, and still expect a high waterline to test any hole that sits too close to the edge. They do not replace the underlay the fitting guides describe.
What if the pond looks full on one side only?
The rim is not level. Water finds the low bank and stops there, so the high bank still shows liner even though the low side looks full. Check the outline again with a spirit level on a straight board, and move soil from the high side to the low side before you trim anything. Cutting the dry bank to match the wet one removes the overlap you still need once the rim is corrected.
When should a landscaper take over?
Call someone in before you dig if the outline crosses drains, cables or any other service, or if the sheet you bought has to be welded on site rather than laid in one piece. A folded liner on a simple hole is the job this page describes. An electric pump is a separate trade: the RHS expects a qualified electrician to handle it. Steep sides, fish and children belong on the wildlife page, where the no-fish rule is set out.

Related pages

Best pond liner for the hole you are lining

Pond membrane

Pond liner buying guide: thickness before the stars

HDPE or rubber pond liner: what a cheap £7 title means

Wildlife pond liner: slope, depth, rain and no fish

Sources

Public UK sources used for this page in October 2026. Prices, stars and review counts are from the twelve amazon.co.uk listings captured on 19 October 2026. A thickness, a 25-year line and a fish sentence are listing claims, not a laboratory result.

  1. RHS, pond construction and repair (retrieved 19 October 2026)
  2. RHS, wildlife ponds (retrieved 19 October 2026)
  3. RSPB, making a wildlife pond (retrieved 19 October 2026)
  4. RSPB shop, wildlife pond guide PDF (retrieved 19 October 2026)
  5. RoSPA, pond safety (retrieved 19 October 2026)
  6. OATA, how to set up a garden pond (retrieved 19 October 2026)
  7. Froglife, Just Add Water (retrieved 19 October 2026)
  8. Consumer Rights Act 2015 (retrieved 19 October 2026)