Calculate required flow rate, turnover time, and target pump capacity using your pond volume, head height, pipe diameter, and fitting restrictions. Visualize water flow in real time.
Total water volume of your pond.
Full pond volume circulated per hour.
Vertical lift from pond surface to return.
Internal diameter of return pipe.
Total length of pipe run.
Wire-to-water efficiency of the pump.
Additional resistance from bends and valves.
Animated particles show relative flow rate. Pipe thickness and colour respond to diameter and resistance.
Required Flow Rate
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0 GPM
0 LPH
Turnover Time
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hours
Target Pump Capacity (at head)
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0 GPM
0 LPH
Important: Actual pump performance depends on the pump curve and system resistance. Always compare your calculated head and flow against the manufacturer's pump curve.
Vertical lift plus friction losses. Every foot of head reduces flow.
Smaller diameter or longer runs increase friction head, reducing flow.
Flow drops as head rises. Find the intersection of your system curve and pump curve.
Pond turnover is the number of times the entire pond volume passes through the pump and filtration system in one hour. For koi ponds, a turnover rate of 1.5–2× per hour is typical; for heavily stocked or high-clarity water, 2–3× is often recommended. Goldfish ponds can often manage with 1–1.5×.
The required flow rate is calculated as: Flow (GPH) = Pond Volume (gal) × Desired Turnover. This gives you the minimum flow your pump must deliver at the actual head height of your system.
Head height is not just the vertical lift. It also includes friction head from pipe length, diameter, and fittings. A pump rated at 2000 GPH at 0 ft might only deliver 800 GPH at 6 ft of total head. That's why using the pump curve is essential.
Pipe diameter matters enormously: doubling the diameter reduces friction loss by a factor of roughly 32 for the same flow. Undersized pipe is one of the most common causes of poor pond circulation.
Our calculator uses the Hazen-Williams equation for friction loss and adds a fitting allowance. It then estimates the required pump capacity assuming a typical efficiency. Always verify with your pump's performance curve.
Formulas used: Turnover time = Pond Volume / (Flow Rate) ; Friction head = f(L/D)(v²/2g) with fitting multipliers.
Hydraulic planning answers for pond owners and installers.
Most koi keepers aim for 1.5 to 2 full turnovers per hour. For high stocking densities or show-quality water clarity, 2–3× is beneficial. Always match turnover to your filtration capacity and fish load.
As head increases, flow decreases. The pump curve shows this relationship. A pump rated at 3000 GPH at 0 ft may only deliver 1200 GPH at 6 ft. That's why you must size the pump based on total dynamic head (TDH), not just advertised flow.
As a rule, use the largest diameter your pump outlet allows, and never smaller than 1.5 inches for flows above 1000 GPH. Increasing pipe size reduces velocity and friction loss dramatically. For long runs, go one size larger than the pump outlet.
Each 90° elbow adds friction equivalent to several feet of straight pipe. Valves add even more. Our calculator includes a fittings allowance based on your selection. Minimise bends and use swept elbows where possible.
Advertised flow is typically measured at zero head. In a real pond, head and friction reduce flow. Manufacturers provide a pump curve showing flow at various heads. Always select a pump whose curve intersects your system's total head at the required flow.
TDH is the sum of vertical lift, friction loss from pipe and fittings, and any pressure head from filters or UV units. Our calculator estimates TDH from your inputs. It's the single most important number for pump selection.
Yes. For waterfalls, head height is the vertical lift to the top of the falls, plus friction. The required flow depends on the width of the weir and desired visual effect. Our calculator helps you find the minimum flow; you may need more for aesthetic spillover.
Most pond pumps operate between 50% and 75% wire-to-water efficiency. Magnetic drive pumps are often lower; direct-drive external pumps can exceed 80%. Check your pump's specifications if available. When in doubt, 70% is a safe conservative estimate.
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