Guide

What size pond pump do I need?

By the Aquarium Calculator team Updated October 9, 2026

Choose a pump that circulates the whole pond at least once every two hours for a plant pond, and once every hour if you keep fish or koi. A 3,600-liter pond (about 950 gallons) needs roughly 1,800–3,600 liters per hour (475–950 GPH), measured at the height the pump has to lift the water, not the figure on the box.

The rule of thumb, with examples

Start with your pond's volume; the pond calculator works it out from length, width and average depth. Then size the pump flow at half the volume per hour for plants only, or the full volume per hour with fish. A 1,000-liter pond needs about 500–1,000 L/h (130–265 GPH); a 3,600-liter pond about 1,800–3,600 L/h (475–950 GPH); a 10,000-liter koi pond about 5,000–10,000 L/h (1,320–2,640 GPH).

Fish, and koi in particular, produce a lot of waste, so a pond with fish needs faster turnover through its filter to keep the water clear and healthy. If you plan to add fish later, size the pump for fish from the start; it's cheaper than replacing it.

Head height: why the box rating isn't the real flow

Pump flow is measured with no height to lift water and no pipework. Every centimeter the pump has to lift water, the 'head' from the pond surface up to the outlet of a filter, waterfall or fountain, reduces the flow, and long or narrow hoses reduce it further. As a rough guide, add about 30 cm of head for every 3 m of hose.

Look at the flow chart on the pump's box or data sheet, find your total head height, and read off the flow at that height. If your outlet is 1.5 m above the water, a pump sold as 5,000 L/h may deliver only half that. Choose a pump that gives your target flow at your real head height, and use wide hose to reduce losses.

Waterfalls and fountains

A waterfall needs enough flow to create a full sheet across its lip. A common guide is about 150 GPH per inch of waterfall width (roughly 220 liters per hour per centimeter) for an average sheet; use about two-thirds of that for a gentle trickle and a third more for a heavy cascade. A 30 cm (12 in) waterfall therefore needs roughly 6,600 L/h (1,800 GPH) for a full sheet.

If the waterfall flow is much higher than the pond's turnover needs, that's fine for the fish, but check that the filter can handle it, or split the flow so only part goes through the filter. Fountains need far less flow but more pressure; follow the fountain head's recommended flow and height.

How deep should a koi pond be?

Koi ponds should be at least 1–1.2 m (3–4 ft) deep and hold 4,000 liters (about 1,000 gallons) or more. Depth keeps the temperature stable through summer heat and winter cold, gives the fish room to swim and turn as they grow to 60 cm or more, and protects them from herons and other predators. In cold climates, the deep zone stays unfrozen and gives koi a safe place to rest in winter.

Goldfish ponds can be shallower, around 60–80 cm (2–2.5 ft), with marginal shelves of 20–30 cm for plants. Whatever the depth, use the deepest point to size the liner and the average depth to calculate the volume; the pond calculator does both and recommends the pump flow.

Filters and running costs

Pair the pump with a filter rated for at least your pond's volume, or more if you keep koi, and ideally a UV clarifier to stop green water. Mechanical filtration catches debris; biological filtration, like in an aquarium, converts fish waste into less harmful compounds, so never clean the biological media with chlorinated tap water.

Pond pumps run around the clock, so efficiency matters. A pump's yearly energy use is its watts × 24 × 365 ÷ 1,000 in kWh: a 50 W pump uses about 438 kWh a year. Compare the flow per watt between pumps, not just the price, because a more efficient pump often pays for itself within a season or two.

Check your own tank

Enter your real dimensions to get exact figures for your setup in a few seconds.

Open the Pond Volume