Water Pump Size Calculator
Flow, total head, pump power and the motor size to fill a tank in time.
Try before you buy.
- Free preview: the rules, dates and checks that apply to your figures, with every computed amount hidden.
- Locked until you unlock it: download and copy.
- Unlock: Pro pass, ₹179 for 30 days or ₹79 for 1 week, a one-time payment that never renews. Unlock: Pro pass, $5.99 for 30 days or $2.99 for 1 week, a one-time payment that never renews.
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Results are estimates from the formulas shown, not a professional design or certification. Have a qualified engineer verify anything safety-critical (structures, electrical installations, gas or pressure systems).
About the Water Pump Size Calculator
Work out the pump you need to fill an overhead water tank in a given time. Enter the tank’s volume and the time to fill it, the suction lift and the delivery height, the pipe’s length and inside diameter, its roughness (the Hazen–Williams C value) and a loss coefficient for its fittings. The calculator finds the flow, the pipe’s friction loss, the total head, the hydraulic power and the shaft power at your pump’s efficiency, and picks the smallest motor rating on your list that covers it.
The free preview shows the result rows with the values hidden; a Pro pass shows every value, with copy and text or JSON downloads.
How to use it
- Enter the tank volume in litres and the time to fill it in minutes.
- Enter the suction lift, the delivery height and the pipe’s length in metres, and its inside diameter in millimetres.
- Check the pipe roughness C, the fittings’ loss coefficient K, any extra head and the pump efficiency, and list the motor ratings you can buy in kW.
- Select Calculate; with a Pro pass, copy the working or download it as text or JSON.
Formulas and source
The flow is the volume divided by the fill time. Pipe friction uses the Hazen–Williams formula in its published US units, h = 4.727 C^−1.852 d^−4.871 L q^1.852 (feet and cubic feet per second, converted exactly), as the US EPA’s EPANET 2.2 manual gives it, and the fittings lose K v² ÷ 2g. Total head = suction lift + delivery height + pipe friction + fittings + any extra allowance. Hydraulic power = ρ g Q H; shaft power = hydraulic power ÷ pump efficiency; the motor is the smallest rating on your list at or above the shaft power.
Limitations
- Hazen–Williams suits water in full pipes in turbulent flow; the C value you enter must match the pipe’s material and age.
- This does not check the pump’s own curve, the suction conditions (NPSH), the motor’s electrical efficiency or its duty: confirm a pump with its maker’s data. An estimate, not a professional pump selection.
Privacy
On this device: nothing is sent
Everything is calculated on your device; nothing is uploaded or stored.
Frequently asked questions
What do I get without a pass?
Without a pass, Water Pump Size Calculator shows the rules, dates and checks that apply to your figures, with every computed amount hidden. Until you unlock it, the result can’t be downloaded or copied. A Pro, Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
Which C value should I use?
It depends on the pipe. The EPANET manual lists 140–150 for new plastic pipe and lower values for rougher materials; older pipes lose some of their smoothness. Use your pipe maker’s figure where you can.
Why is the motor bigger than the pump power?
The shaft power already includes the pump’s efficiency. The calculator then picks the next rating on your list, because motors come in fixed sizes; it never picks a smaller one.