How do I calculate pond volume in litres?

For a roughly rectangular pond, multiply its average length by average width by average depth in metres, then multiply the cubic metres by 1,000 to get litres. This follows the calculation published by the RHS.

Use average depth, not maximum depth. A pond with beaches and shelves holds less than a box with the same outside length, width and deepest point. For an irregular pond, measure in several places and use realistic averages; the result remains an estimate. An oval needs an ellipse adjustment, which the site's calculator handles.

Volume matters because pump flow, filter capacity and water treatments are normally specified against litres. Measure rather than guessing from the liner or the hole. Keep the dimensions with the pond records so you do not have to reconstruct them when equipment is replaced.

The pond planner calculates rectangular, oval and irregular volumes in the browser. It does not send the measurements anywhere.

A worked method without guessed precision

Measure the water, not the decorative outer edge. Take length and width at several points and depth at the shallow, middle and deeper areas, then form sensible averages. Write those measurements beside the calculated result. If the pond is filled through a metered supply, a water meter can provide a second check, but allow for any water used elsewhere. Round the final number sensibly: a highly irregular hole cannot be known to the nearest litre from three tape measurements. Use the cautious result when comparing equipment capacity.

Recalculate after a major rebuild changes the shelves or depth.

Sources

• RHS: choosing a pond filter — accessed 14 November 2026.

More from Pond Setup Guide

Use how big should a garden pond be? for design decisions and pond pump sizing after you know the litres. Pond volume and turnover are defined in the pond glossary.