Pond Liner Calculator
Pond liner and underlay size, water volume and pump flow for a garden pond.
About this tool
Enter the pond's longest length, widest width and deepest depth, plus how much liner to leave at each edge. The tool gives the liner and underlay size, an estimated water volume in litres and US and UK gallons, and a minimum pump flow. Choose the shape (straight-sided, sloped with shelves, or a natural bowl) for a better volume estimate.
How to size a pond liner
A flexible liner has to line the bottom and climb both sides, then lap over the edge to be held down by stones, slabs or turf. The formula is liner length = pond length + 2 ร deepest depth + 2 ร overlap, and the same for the width. A pond 3 m long, 2 m wide and 0.6 m deep with a 30 cm overlap needs a 4.8 ร 3.8 m liner (or 10 + 4 + 2 = 16 ft by 6.5 + 4 + 2 = 12.5 ft in imperial). Marginal shelves and sloping sides don't need extra: the depth term already allows for the liner following them, provided you measure the longest, widest and deepest points. EPDM rubber is the most durable and flexible choice and is fish-safe. PVC is cheaper but stiffer and shorter-lived. Lay underlay or old carpet the same size underneath to protect against stones and roots. Water volume matters for pumps, filters, UV clarifiers, fish stocking and treatments. A straight-sided box holds length ร width ร depth, but most garden ponds hold about 60โ75% of that, and the shape setting allows for this. Size the pump to move the whole volume at least every two hours, or every hour for fish ponds, allowing for head height and pipe losses. Honest limits: round up to the next size your supplier sells, allow a little more for very irregular shapes, and for accurate dosing measure the volume when you first fill. The pool volume calculator, the rainwater harvesting calculator and the concrete calculator are related.
Frequently asked questions
How do I calculate pond liner size?
Length + 2 ร depth + 2 ร overlap, by width + 2 ร depth + 2 ร overlap. For a 3 ร 2 ร 0.6 m pond with 30 cm overlaps, that's 4.8 ร 3.8 m.
How much overlap should a pond liner have?
About 30 cm (12 inches) on each side is typical, so it can be tucked under edging.
What size pump do I need for a pond?
One that moves the pond's volume at least every two hours, or every hour if you keep fish, after allowing for the height it pumps to.
Is anything stored?
No. Calculations run in your browser and nothing is stored or sent.