Pump Head and Input Power Calculator
Add up the head a water pump must deliver at its duty point and turn it into the electrical power the motor will draw. Every figure is yours — the flow, the heads from your levels and pipe calculation, and the efficiencies from the pump curve and motor datasheet.
What this tool estimates
The total head at the design flow — static lift plus friction plus the residual pressure needed at delivery — and the hydraulic, shaft and electrical input power at that duty point for the density and efficiencies you enter.
What it cannot decide
- Which pump to buy: the duty point has to sit on a real pump curve, close to its best-efficiency region.
- Whether the suction side is safe — NPSH available against the pump's NPSH required is a separate check.
- The friction head itself: it comes from a pipe calculation for this flow through the actual pipes, fittings, valves and strainers.
- The motor rating, starting method, standby pumps or how pumps share the duty in parallel.
Result
The shaft power is not a motor rating: a motor is chosen against the most power the pump can draw across its curve, not this one point.
| Step | Value |
|---|
| Friction head |
|---|
Method version 6 October 2026. A screening estimate, not a design: see the limits below.
How this calculator works — and where it stops
What it calculates
The total head a water pump must deliver at its duty point and the power that takes: the hydraulic power given to the water, the shaft power the pump needs, the electrical power the motor draws, and the electricity used per m³ pumped.
Inputs
- Design flow at the duty point, in m³/s, m³/h, L/s or L/min.
- Static lift (m): from the lowest water level pumped from to the highest point of delivery.
- Friction head (m) at that flow, from your own pipe calculation of the route — pipes, fittings, valves, strainers and meters. The tool does not estimate it.
- Residual pressure needed at delivery, as head (m) or in bar or kPa; pressures are turned into head with the density you enter.
- Fluid density (kg/m³) at its temperature.
- Pump efficiency at the duty point (from the pump curve) and motor efficiency (from the motor datasheet), each more than 0 and at most 1.
Method
- Total head H (m) = static lift + friction head + residual head. A residual pressure in bar or kPa becomes head as pressure in Pa ÷ (density × 9.80665).
- Hydraulic power (kW) = density × 9.80665 × Q (m³/s) × H ÷ 1000, where 9.80665 m/s² is the standard acceleration of gravity.
- Pump shaft power (kW) = hydraulic power ÷ pump efficiency, also shown in horsepower of 745.7 W.
- Electrical input (kW) = shaft power ÷ motor efficiency = density × 9.80665 × Q × H ÷ (1000 × pump efficiency × motor efficiency).
- Electricity per m³ (kWh/m³) = electrical input ÷ flow in m³/h.
- Sensitivity: the input power is recomputed with the friction head at −25%, +25% and +50%, and the pump efficiency 0.10 either side (a value above 1 is dropped).
Assumptions
- The flow and head describe one steady duty point. A system whose demand swings runs at other points on the pump curve, at other efficiencies.
- The efficiencies apply at this duty point. A brochure's best-efficiency figure overstates a pump that runs away from its best point.
- The input is at the motor terminals: losses in a drive (VFD), starter, cables or transformer are not included.
- A residual pressure in bar or kPa is the gauge pressure needed at the delivery point.
Limitations
- Does not select a pump: the duty point has to be checked against real pump curves, ideally close to the best-efficiency point.
- Does not check NPSH. Suction lift, suction-pipe losses, fluid temperature and vapour pressure decide whether the pump cavitates — a separate check against the pump's NPSH required.
- Does not calculate friction head, pipe sizes or velocities; use a pipe calculation, and the water pipe velocity sizing calculator for the bore.
- Does not size the motor — chosen from the most power the pump can draw across its curve, not one duty point — nor the starter, standby pumps or parallel operation.
- Water supply for fire-fighting and industrial plants is outside NBC 2016 Part 9 Section 1, as BIS's guide to the code notes; fire and process pumps need their own design basis.
Worked example
Produced by running this calculator with the inputs below.
Inputs
- Design flow 0.01 m³/s (36 m³/h)
- Static lift 20 m, friction head 6 m, residual 4 m — illustrative
- Water at 1,000 kg/m³
- Pump efficiency 0.70 and motor efficiency 0.90 at the duty point
Working
- Total head = 20 + 6 + 4 = 30 m.
- Hydraulic power = 1,000 × 9.80665 × 0.01 × 30 ÷ 1000 = 2.94 kW.
- Shaft power = 2.94 ÷ 0.70 = 4.20 kW (5.64 hp).
- Electrical input = 4.20 ÷ 0.90 = 4.67 kW — the same as 1,000 × 9.80665 × 0.01 × 30 ÷ (1000 × 0.70 × 0.90).
- Electricity per m³ = 4.67 ÷ 36 = 0.130 kWh/m³.
Result. 30 m of total head and 4.67 kW of electrical input at the duty point — an overall efficiency of 63%, or 0.130 kWh for every m³ pumped.
Sensitivity — what moves the answer
- In the worked example the pump efficiency moves the answer most: at 0.60 the same duty needs 5.45 kW, at 0.80 it needs 4.09 kW.
- Friction head is usually the least certain input: if the 6 m is really 9 m (+50%), the head is 33 m and the input 5.14 kW.
- Power is directly proportional to flow, head and density: 10% more of any one is 10% more power.
How engineers use the result
To put a number on a pumping duty before selection: the head and power it implies, what an efficiency or friction assumption is worth in kW and kWh per m³, and whether an existing pump and motor are in the right range for an expansion.
When a professional design must replace it
Before ordering a pump or motor: an engineer should confirm the friction head from the actual pipe routing, plot the system curve against candidate pump curves, check NPSH available against required, select the motor from the curve's maximum power, and settle the duty/standby arrangement.
Sources
- NIST — CODATA value: standard acceleration of gravity, 9.806 65 m/s² (exact) — the g in the hydraulic power
- Hydraulic power = ρ × g × Q × H; shaft power = hydraulic ÷ pump efficiency; input = shaft ÷ motor efficiency — definitions; no code clause is applied by this tool
- BIS — Guide for using National Building Code of India 2016, Part 9 (Plumbing Services) — Section 1 (water supply) covers building occupancies and excludes water supply for fire-fighting, street cleaning and industrial plants
Questions people ask before using it
What information do I need before using the pump head calculator?
The design flow at the duty point; the static lift, measured from the lowest water level you pump from to the highest point of delivery; the friction head at that flow from a pipe calculation of the actual route, including bends, valves, strainers and meters; the residual pressure needed at the critical outlet or equipment inlet; the density of the fluid at its temperature; and the pump and motor efficiencies at that duty point, read from the pump curve and the motor datasheet rather than the brochure's best figure.
Which site conditions could change the pump power result?
A sump drawn lower than you assumed (static lift is measured from the lowest level), pipes that scale or corrode and add friction over the years, a higher residual pressure demanded by new equipment, a duty point that sits away from the pump's best-efficiency region, hot water or fluids other than clean water (density and the NPSH margin change), and throttled or VFD-controlled operation that moves the operating point along the curve.
What should I send an engineer for a pumping review?
The site water balance with peak and average flows and the shifts or occupancy behind them, a schematic of the pumping route with pipe sizes, lengths, fittings and the levels of the source and delivery points, the residual pressures required, the duty/standby arrangement you intend, and — for a replacement — the existing pump and motor nameplates, the pump curve and any energy or flow readings.
Optional: ask an engineer to look at it
The result above is yours with no form. If you want an engineer to check it against your drawings, schedules or bills, send a request. Nothing is sent until you press the button.
Request saved
It reached our team with exactly what the preview showed. An engineer will use the number you gave if they need your drawings or data.
Prefer to talk? WhatsApp or the contact form.
Got your number — what next?
A calculator gives you a first figure. These take it further.
The work itself
Read before you specify
The terms behind it
Delivered work with this scope
- Full MEPF Package for JMH Prime, Jeewan Mala Hospital — Karol Bagh, New Delhi — Jeewan Mala Hospital
- MEPF for Advantec Wheels Alloy Plant, Jammu — Advantec Wheels
Related calculators
One of 56 free MEPF and solar calculators on this site. Every input term is defined in the engineering glossary; the specification libraries, clearance guides and checklists for design teams are in the architects' section.
Guides that reference this page
- Fire Pump Set for a Factory: Duty, Standby, Jockey and Cost Drivers
- Factory Expansion Water Demand: Domestic, Process, Peaks and Storage
- Why the 3rd Floor Gets a Trickle, the 1st Floor Gets a Jet, and the Pipes Bang at Night
- Water Reuse in Factories: Building a Savings Case That Holds Up
- The Most Dangerous Electrical Installation You Will Ever Own Is the Temporary One
- Captive vs Open Access Solar: Which Route for a 1 MW+ Consumer
Related on this site
- termDLP (Defect Liability Period)
- termString Inverter vs Central Inverter
- termOpen Access (Solar)
- serviceCCTV & IP Video Surveillance (Low Voltage / ELV)
- serviceBattery / Hybrid Storage (Solar EPC)
- calculatorCctv Storage Calculator
- calculatorSolar Shadow Free Area Calculator
- buyer's guideHow to Compare MEPF Quotations
- guideFactory licence and DISH approval
- guideCTE/CTO pollution consent