Waterfall Pump Flow Calculator
Size a pond or waterfall pump — the flow you need from spillway width, and the turnover your pond volume demands.
How it works
Waterfall flow = spillway width × flow per inch · Turnover flow = pond volume (once per hour) · Pump flow = max of the two, rated at the head height
A waterfall pump has to satisfy two demands at once: enough flow to make the falls look right, and enough to circulate the whole pond about once an hour for healthy water. Spillway flow is roughly 100–150 gallons per hour for every inch of width; hourly turnover just equals the pond volume. Take the larger figure — but read it off the pump’s flow-at-head chart, because every foot of lift and every elbow of pipe cuts a pump’s rated output.
Worked example
A 12-inch spillway at 125 GPH/in needs 1,500 GPH for the look. A 500-gallon pond needs only 500 GPH for turnover, so the waterfall governs: choose a pump delivering at least 1,500 GPH at 4 ft of head, not its zero-lift maximum.
Frequently asked questions
How many GPH do I need per inch of waterfall?
Plan for about 100 gallons per hour per inch of spillway width for a gentle sheet, 150 or more for a full, loud cascade. Wider or taller falls need proportionally more.
What is head height and why does it matter?
Head is the total vertical lift from the pump to the top of the waterfall, plus friction from pipe and fittings. Pumps lose flow as head rises, so a pump rated 2,000 GPH at 0 ft may deliver far less at 5 ft — always size from the flow-at-head chart.
How often should pond water turn over?
Aim to circulate the entire pond volume at least once per hour. Ponds with fish or heavy waterfalls benefit from faster turnover; that is why this tool uses the larger of the waterfall and turnover requirements.
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This calculator is for educational purposes. Double-check important results before acting on them.