Waterfall Flow Chart (GPH by Spillway Width)
Waterfall flow chart: GPH needed at the top of the falls by spillway width from 6 to 48 inches, using 1,000 GPH per foot for a trickle, 1,500 for an average sheet, and 2,000 for a strong sheet, plus a head-height pump sizing table.
Quick answer: A waterfall needs 1,000 to 2,000 GPH per foot of spillway width, measured at the top of the falls: about 1,000 GPH per foot for a gentle trickle, 1,500 for an average sheet, and 2,000 for a strong full sheet. So a 24 inch spillway with an average sheet needs roughly 3,000 GPH arriving at the top. Then add about 12 percent rated flow per foot of head height when choosing the pump.
This chart answers the two questions every waterfall build comes down to: how much flow does my spillway width need for the look I want, and how big a pump do I buy so that flow actually arrives after climbing the falls. The width table gives flow at the top of the falls for three looks, and the head table converts that into the rated pump size to shop for.
For your exact width, head height, and hose run, the waterfall pump calculator runs these numbers in one step, and the pondless waterfall calculator covers basin sizing for pondless builds.
Waterfall flow chart by spillway width
Flow needed at the top of the falls. Trickle = 1,000 GPH per foot of width, average sheet = 1,500, strong sheet = 2,000.
| Spillway width | Trickle (GPH at top) | Average sheet (GPH at top) | Strong sheet (GPH at top) |
|---|---|---|---|
| 6 in (0.5 ft) | 500 | 750 | 1,000 |
| 8 in | 670 | 1,000 | 1,330 |
| 10 in | 830 | 1,250 | 1,670 |
| 12 in (1 ft) | 1,000 | 1,500 | 2,000 |
| 16 in | 1,330 | 2,000 | 2,670 |
| 18 in (1.5 ft) | 1,500 | 2,250 | 3,000 |
| 24 in (2 ft) | 2,000 | 3,000 | 4,000 |
| 30 in (2.5 ft) | 2,500 | 3,750 | 5,000 |
| 36 in (3 ft) | 3,000 | 4,500 | 6,000 |
| 48 in (4 ft) | 4,000 | 6,000 | 8,000 |
Pump rating by head height
Pumps are rated at zero head, so multiply the flow you need at the top by the factor for your total head height. The example column sizes a pump for a 24 inch spillway with an average sheet (3,000 GPH at the top).
| Total head height | Rated flow multiplier | Example: pump rating for 3,000 GPH at top |
|---|---|---|
| 1 ft | 1.12x | 3,360 GPH |
| 3 ft | 1.36x | 4,080 GPH |
| 5 ft | 1.60x | 4,800 GPH |
| 7 ft | 1.84x | 5,520 GPH |
| 10 ft | 2.20x | 6,600 GPH |
| 15 ft | 2.80x | 8,400 GPH |
The multiplier uses the planning rule of about 12 percent extra rated flow per foot of head. It gets you shopping in the right class; the final check is always the manufacturer's flow-vs-head curve, which shows the real delivered GPH at your exact head height.
Waterfall Pump Picks
OYO Water 3000 GPH Submersible Pond Pump, 175W
$109.99 on Amazon
High-flow pump class for 18 to 24 inch spillways once head loss is covered.
Half Off Ponds Aqua Pulse Submersible Pond Pump, 3,000 GPH
$144.00 on Amazon
Heavy-duty 3,000 GPH pump with a 33 ft cord for waterfall and stream duty.
How to measure your total head
Total head has two parts. Static head is the straight vertical distance from the pond surface up to the lip of the spillway. Dynamic head is plumbing friction, estimated at about 1 foot of equivalent head for every 10 feet of horizontal hose, plus a small allowance for each elbow, check valve, or tee. Add the two together and use that figure in the table above. Skimping here is the classic reason a new waterfall arrives as a disappointing dribble even though the pump box promised huge flow.
Waterfall flow vs filter turnover
The waterfall number and the filtration number are different jobs that happen to share a pump in many builds. Your filter loop should turn the whole pond over at least once per hour, covered in the pump turnover chart. If the flow your spillway wants is far above your turnover need, run a second dedicated waterfall pump instead of over-driving the filter, and if it is below, the falls can simply ride the filter return. Building the falls itself, weir box, liner, and stone, is covered step by step in the pondless waterfall build guide.
Sizing flow for an indoor tank instead? Our sister site FishTankCalculator.com covers aquarium pumps and filtration rates.
Frequently Asked Questions
How many GPH do I need per inch of waterfall?
The standard rule is 1,000 to 2,000 gallons per hour for every foot of spillway width, which works out to roughly 85 to 165 GPH per inch. A gentle trickle wants about 1,000 GPH per foot, an average sheet of water about 1,500, and a strong full sheet that completely covers the lip 2,000 or more. Measure the width at the top of the falls where the water pours over, and remember this is flow arriving at the top, after head loss.
What does GPH at the top of the falls mean?
It is the flow that actually reaches the spillway after the pump has fought gravity and pipe friction, and it is the number the whole chart is built on. Pumps are rated at zero head, so a 3,000 GPH pump does not deliver 3,000 GPH up a 6 foot waterfall. Size the look you want from the width table first, then buy a pump rated high enough that its flow curve still shows your target at your real head height.
How much extra pump capacity does head height require?
A practical planning buffer is about 12 percent more rated flow for every foot of head. A waterfall needing 3,000 GPH at the top with 5 feet of head calls for a pump rated near 4,800 GPH at zero head. This is an estimate for shopping, not a law of physics, so always confirm on the specific pump's flow-vs-head curve that it still delivers your target at your total head.
How do I measure head height for a waterfall?
Total head is the vertical rise plus friction. Measure straight up from the pond surface to the lip of the spillway for static head, then add roughly 1 foot of equivalent head for every 10 feet of horizontal hose run and a little more for each elbow or valve. A falls 4 feet above the pond fed by 20 feet of hose behaves like about 6 feet of head, and that is the number to check on the pump curve.
Can a waterfall pump be too big?
Yes. Oversizing wastes electricity around the clock, can blast water past the spillway edges and splash it out of the system, and creates currents that koi have to fight. If you want both a big waterfall and correct filter turnover, the cleaner design is two pumps: one sized for the filter loop and a separate one dedicated to the falls, each sized to its own job.
How wide should a waterfall spillway be?
Pick the look first, then the pump. A 6 to 12 inch spillway gives a focused, bubbling stream and runs on a small, cheap pump. An 18 to 24 inch spillway is the classic backyard sheet of water. Anything 30 inches and wider is a statement piece that demands 4,000 GPH or more at the top and a serious pump. Wider is dramatic but the power bill scales right along with the width.
Planning or running a pond?
Use our free calculators and guides to get every number right.
Pond Planner: $39