Pump Sizing Calculator

Calculate Differential Head, Power & NPSH


Identification Data

Tagname
Site
Area
Notes

Fluid Properties

Fluid
Liquid Flow Rate
gpm
Density
lb/ft³
Dynamic Viscosity
cP
Vapor Pressure
psia
Pump Efficiency %

Suction Side

Operating Pressure
psia
Static Head
ft
Equipment Pressure Loss
psi
Pipe Length
ft
Pipe NPS Schedule 40

Suction Fittings

Elbows, 90° LR Elbows, 45° LR
Tees, Thru Tees, Branch
Gate Valve Pipe Entrance

Discharge Side

Operating Pressure
psia
Static Head
ft
Equipment Pressure Loss
psi
Pipe Length
ft
Pipe NPS Schedule 40

Discharge Fittings

Elbows, 90° LR Elbows, 45° LR
Tees, Thru Tees, Branch
Gate Valve Check Valve
Pipe Exit

How the Pump Sizing Calculator works?

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All of our calculators work in a similar way. First you will find a block of information called "Identification Data". In this block we ask you to indicate the Tag, the Plant where the pump is located and the Area. You also have the possibility to add some notes. This information will be attached to the report if you wish to provide it. It is not necessary to perform the calculation.
The next block of information is called "Fluid Properties". In this block we ask you to indicate the name of your fluid, flow rate, density, viscosity, vapor pressure, and pump efficiency. These properties are essential for accurate hydraulic calculations.
The "Suction Side" and "Discharge Side" blocks allow you to define the piping system including operating pressures, static heads, equipment losses, pipe lengths, pipe sizes, and fittings. The calculator uses these inputs to determine friction losses through the piping system.
Once everything is set you must click on Calculate! button. Then, all the resulting cells will be calculated including differential pressure, differential head, hydraulic power, brake power, and NPSH available. You can press this button until your results are inline with your expectations. Once everything is correct you can export your work to PDF document containing all your parameters and results. To be able to obtain this file you must click on Download button.
We hope you enjoy using this calculator.

Information and Definitions

Differential Head The difference in head between the discharge and suction sides of a pump, representing the total energy per unit weight of fluid that the pump must provide to move the fluid through the system.
NPSH Available Net Positive Suction Head Available - The absolute pressure at the pump suction minus the vapor pressure of the liquid, expressed as head. It must be greater than NPSH Required to prevent cavitation.
Brake Power The actual power required at the pump shaft, calculated by dividing the hydraulic power by the pump efficiency. This is the power that the motor must deliver to the pump.
Hydraulic Power The theoretical power required to move the fluid through the system, calculated from the flow rate, fluid density, and differential head. Also known as water horsepower.
Reynolds Number A dimensionless number used to predict flow patterns in pipes. It determines whether the flow is laminar (Re < 2300) or turbulent (Re > 4000), which affects friction factor calculations.
Friction Factor A coefficient used in the Darcy-Weisbach equation to calculate pressure drop in pipes. It depends on the Reynolds number and the pipe's relative roughness.
Static Head The vertical distance between the liquid surface and a reference point (usually the pump centerline). Positive static head on suction adds to available pressure; positive static head on discharge adds to required discharge pressure.
Pump Efficiency The ratio of hydraulic power output to mechanical power input, expressed as a percentage. Typical centrifugal pump efficiencies range from 50% to 85% depending on size and design.

Frequently Asked Questions

Q1 What is NPSH and why is it important?
A1 NPSH (Net Positive Suction Head) represents the absolute pressure available at the pump suction above the vapor pressure of the liquid. If NPSH Available falls below the pump's NPSH Required, the liquid will flash to vapor (cavitation), causing severe pump damage, reduced performance, and noise. Always ensure NPSHa exceeds NPSHr by a reasonable margin.
Q2 How do I determine the correct pipe size for my pump?
A2 Pipe sizing involves balancing capital cost against operating cost. Larger pipes reduce friction losses but cost more. For suction piping, velocities should typically be below 5 ft/s to minimize friction losses and maximize NPSH. Discharge piping can handle higher velocities (8-12 ft/s) depending on the application. Use this calculator to verify that your pipe selection provides acceptable pressure drops.
Q3 What pump efficiency should I use in calculations?
A3 Pump efficiency varies by pump type, size, and operating point. Small pumps (< 10 gpm) may have efficiencies of 30-50%, while large pumps can exceed 85%. Use the manufacturer's pump curve to find efficiency at your operating point. For preliminary sizing, 50-70% is a reasonable estimate for centrifugal pumps.
Q4 How do fitting losses affect pump sizing?
A4 Fittings such as elbows, tees, valves, and reducers create additional pressure drop beyond straight pipe friction. These losses can be significant in systems with many fittings or high velocities. The calculator uses K-factors based on the 2-K method to estimate fitting losses, which accounts for Reynolds number effects for better accuracy.
Q5 What is the difference between hydraulic power and brake power?
A5 Hydraulic power (also called water horsepower) is the theoretical power needed to move the fluid. Brake power is the actual power the motor must deliver to the pump shaft, accounting for pump inefficiency. Brake power = Hydraulic power / Efficiency. The motor must be sized larger than the brake power requirement, typically by 10-25%.