Pond planner

The result is a planning figure, not a shopping order. Indicative only — always check the maker's ratings and instructions.

What the numbers are doing

• Volume. Rectangle and irregular ponds use length × width × average depth × 1,000. An irregular pond is just your average length and average width, which is a rough figure. An oval uses the area of an ellipse, π/4 × length × width, then the average depth. PondXpert's published example is a box: 3 × 2 × 1 × 1,000 = 6,000 litres. Average depth is used so a shelf is not counted as if the whole pond were at the deepest point.
• Liner. Length and width each gain twice the maximum depth, plus 0.5 m of overlap on every side. That 0.5 m is Gordon Low's "50 cm on each edge". All Pond Solutions talks about 30–50 cm past the edge and says to round up.
• Pump. PondXpert says goldfish ponds should turn over once every two hours, so the flow is half the volume per hour. Koi turn over once an hour, so the flow matches the volume. A wildlife pond with no fish does not get a filter flow. The RHS says ponds with few or no fish should not need a filter.
• Head. The flow you need is the flow at the real height, not the maximum printed at zero head. Hozelock's Vorton instruction booklet tells you to take the vertical distance from the pond surface to the filter inlet and add 0.6–0.9 m for hose friction. The result shows that range.
• Filter. For goldfish, look for a unit rated for at least your volume on the fish line. For koi, PondXpert wants a box filter, not a pressure filter, rated to the pump. Wildlife: usually none.
• UV. The bands are the Hozelock Vorton range as listed on the maker's page on 13 November 2026: 11 W up to 4,000 litres, 18 W up to 6,000, 36 W up to 12,000, 55 W up to 18,500, with the recommended flows shown beside them. Above that, use a larger maker's chart. Wildlife ponds are not given a UV by default.
• Running cost. Watts × 24 × 365 ÷ 1,000 gives kWh per year if the pump never switches off. Multiplied by the pence-per-kWh figure, that is pounds. The default 26.32p is the Ofgem Direct Debit average for England, Scotland and Wales from 1 October to 31 December 2026. It is not your bill, and it excludes the standing charge. Electricity VAT is not included in that cap period.

Safety sits in the result on purpose

Every result links to the child-safety guide and to RoSPA. A correct pump size does not make a pond safe for a toddler.

The guides behind each line are how big the pond should be, liner size, pump size, filter size, UV size and electrics.