H2X Tools

Pressure Drop Calculator

Learn everything about pressure drop, understand the Darcy Weisbach formula, and use our free pressure drop calculator.

Introduction to Pressure Drop

Pressure drop is a critical aspect in various industries, including oil and gas, HVAC, plumbing, and many others.

It refers to the decrease in pressure as fluid or gas moves through a pipe.

Pressure drop calculations are crucial for ensuring efficient operation and preventing damage to equipment.

With advancements in technology, pressure drop calculations have become much easier with a pressure drop calculator.

This article will explore everything you need to know about pressure drop, its calculations, and how a pressure drop calculator can help.

Whether you're a seasoned professional or just starting, this guide will give you a comprehensive understanding of pressure drop and its calculations.

Pressure Drop calculator
Friction Loss chart

Factors Affecting Pressure Drop

Several factors affect pressure drop calculations, including:


  • Pipe diameter: A larger pipe will result in a lower pressure drop, while a smaller pipe will result in a higher pressure drop.
  • Pipe length: A longer pipe will result in a higher pressure drop, while a shorter pipe will result in a lower pressure drop.
  • Pipe roughness: A rougher pipe will result in a higher pressure drop, while a smoother pipe will result in a lower pressure drop.
  • Fluid viscosity: A more viscous fluid will result in a higher pressure drop, while a less viscous fluid will result in a lower pressure drop.
  • Fluid velocity: A higher-velocity fluid will result in a higher pressure drop, while a lower-velocity fluid will result in a lower pressure drop.


The pressure, after the friction loss, can be measured in:

  • Bar
  • kPa
  • psi
  • Metre head
  • Feet head

How to Calculate Pressure Drop

Calculating pressure drop can be complex and time-consuming, especially if you don't have the right tools.

Various equations and formulas can be used to calculate pressure drop, but using a pressure drop calculator is the easiest and most efficient method.

A pressure drop calculator takes into account all the relevant factors affecting pressure drop and provides you with an accurate and reliable calculation. This eliminates the need for manual calculations and reduces the risk of errors.

The Darcy Weisbach formula/equation is the most accurate equation for calculating the friction loss/pressure drop in a pipe and is the industry standard.

The Darcy Weisbach Equation

The following Darcy Weisbach equation can be used to calculate the pressure drop in a pipe:

Hf = f L v²/ 2gD

Components of the Equation

hf = Head loss in a pipe (m or ft)

L = Pipe length (m or ft)

V = velocity of the fluid inside the pipe (m/s or ft/s)

D = pipe internal diameter (m or ft)

f = friction factor {f = [1.14 + 2 log10(D/e)]-2} and then iteratively f = {-2*log10[((e/D)/3.7)+(2.51/(Re*(f1/2))]}-2

g = gravity (m/s² or ft/s²) , which has a constant value of approximately 9.8 m/s².

Use h2x for Pressure Drop Calculations

Calculates the pressure drop through every pipe (CIBSE-verified)

Calculates the pressure drop through every valve and fitting (CIBSE-verified)

Automates all of the calculations based on your design layout

h2x is CIBSE-verified design software built to improve the efficiency and quality of your design process.

The automated calculations for flow rates, velocities, pressures, pump duties, plant sizing, and recirculation systems mean that you can focus on your project’s design instead of undertaking tedious calculations.

The straightforward user interface helps engineers produce high-quality designs and work more efficiently, all while adhering to industry regulations.

The software has already been used to size millions of kilometres of pipes in projects across the world.

Why Use a Pressure Drop Calculator?

There are several benefits to using a pressure drop calculator, including:


  • Saves time and effort: A pressure drop calculator can quickly and easily calculate pressure drop, eliminating the need for manual calculations.
  • Increases accuracy: Pressure drop calculators use the latest algorithms and formulas to provide you with accurate and reliable calculations, reducing the risk of errors.
  • Improves efficiency: By providing quick and accurate pressure drop calculations, a pressure drop calculator can help you make informed decisions and improve the efficiency of your operations.


See what H2X can do

There's a reason our pipe sizing software is rated 4.9/5 for customer support.


The integrated help button means a real engineer will promptly assist with any design query.