IES
Mechanical Engineering2D

Pump Sizing Calculator

Size a centrifugal pump by calculating required power from design flow, head, efficiency, and safety margin.

Inputs
Enter your values below

0.75 = 75% at BEP

1.1-1.25 typical

Result
Required Motor Power
—
Enter values and click Calculate
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Formula
density × flow × 9.81 × head ÷ efficiency × safety ÷ 1000
Result unit: kW

Required Power = ρQgh/(η) × safety. /1000 converts W to kW for the final answer. Safety factor typically 1.1-1.25.

Introduction

Calculate the required motor power for a centrifugal pump given design flow, total head, efficiency, and a safety margin. Round up to the nearest standard motor size (5.5, 7.5, 11, 15, 18.5, 22, 30, 37, 45, 55, 75 kW).

How This Calculator Works

Required Power = ρQgh/(η) × safety. /1000 converts W to kW for the final answer. Safety factor typically 1.1-1.25.

Step-by-step process:

  1. Enter your input values in the calculator above
  2. The engine converts all inputs to SI base units (meters, kg, Pa)
  3. The formula is evaluated: density * flow * 9.81 * head / efficiency * safety / 1000
  4. Result is formatted with the appropriate unit and precision

Calculation Example

100 m³/h × 50m at 75% efficiency with 15% safety: 20.9 kW. Select a 22 kW standard motor.

Inputs: flow=100, head=50, density=1000, efficiency=0.75, safety=1.15
Result: 20.9 kW

Unit Conversion for Pump Sizing

**Head units**

- 1 m = 3.28084 ft

- 1 ft = 0.3048 m

**Flow units**

- 1 m³/h = 0.2778 L/s = 4.403 US gpm

- 1 US gpm = 0.2271 m³/h

**Power units**

- 1 kW = 1.341 hp

- 1 hp = 0.7457 kW

**NPSH units**

- 1 m = 3.28084 ft

Pump sizing combines flow, head, and NPSH requirements. Convert all values to one consistent unit system (metric or imperial) before selecting from a pump curve.

Engineering Applications

  • •Pump motor sizing
  • •Equipment specification
  • •Capital cost estimating
  • •Procurement

Frequently Asked Questions

What safety factor should I use?

1.1-1.15 for well-defined systems with accurate pressure drop calcs; 1.2 for conservative estimates; 1.25+ for high-viscosity or uncertain conditions.

How do I select standard motor size?

IEC standard sizes: 0.75, 1.1, 1.5, 2.2, 3, 4, 5.5, 7.5, 11, 15, 18.5, 22, 30, 37, 45, 55, 75, 90, 110 kW. Round up to nearest size.

How do I convert head and flow units for pump sizing?

Convert head: 1 m = 3.28084 ft. Convert flow: 1 m³/h = 4.403 gpm. Convert power: 1 kW = 1.341 hp. Always size using the same unit system as the pump curve to avoid errors.

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Engineering Disclaimer: Calculations are for reference and educational purposes only. Always verify results independently for engineering design. See full disclaimer.
Reviewed by: Industrial Engineering Team
References: ASME B31.3, ASTM A36, Perry's Chemical Engineers' Handbook