Pressure drop calculator

incompressible flow, losses due to friction calculation

online since 2006

Registration and subscription

Select a subscription plan and enable the full service:

  • Switch between metric and imperial units in one click
  • Export calculation results in Word .docx or Excel .xlsx format
  • Preview results on one place and copy/paste it in your favorite text editor
  • Send results back to your email
  • Support the future of this project

And even more... Subscribed users have access to the full set of 19 calculators available as Java™ Web start application or download Windows™ 64bit application.

Select the annual subscription and enable full service for only 0.05 USD/day Subscribe

Annual subscription

from $0.05 / day

total cost for one year $18.25

Calculation setup
Flow rates
Flow regime: Flow is turbulent
Pipe dimensions
Fluid properties

Exclusive calculator

On exclusive calculator page you can use the online calculator without interference from advertisements, additional text, links and other content that is not required for the calculations themselves. A pure experience of using a calculator as with a desktop application.

An exclusive version of the calculator is available to registered users. Choose the right subscription duration and start using the exclusive service.



p1 - inlet pressure
Absolute pressure at the pipe start
p2 - outlet pressure
Absolute pressure at the pipe end
Δp - pressure drop
Pressure difference between pipe start and pipe end
q - volume flow rate
Fluid flow rate in terms of units of volume per unit of time
ṁ - mass flow rate
Fluid flow rate in terms of units of mass per unit of time
L - pipe length
Length of a pipe in which pressure drop is calculated
D - pipe diameter
Internal circular pipe diameter
H - channel height
The height of channel for rectangle shaped pipe
W - channel width
The width of channel for rectangle shape pipe
kr - pipe roughness
Pipe internal surface roughness
V - velocity
Flow velocity in terms of units of distance per unit of time
A - area
Internal pipe cross section area
f - friction coefficient
Coefficient of friction for pressure drop due to friction calculation
Re - Reynolds number
Dimensionless number representing viscous versus inertial forces ratio
δ - boundary layer
Thickness of laminar layer formed in turbulent flow connected to pipe wall surface
ρ - fluid density
Mass per unit of volume
ν - kinematic viscosity
Result of fluid particles colliding to each other and moving at different velocities in terms of area per square unit of time
μ - dynamic viscosity
Result of fluid particles colliding to each other and moving at different velocities in terms of mass per square unit of distance and time
K - resistance
Coefficient used for calculation of minor losses due to local resistances in pipe line like bends, tees, reducers, valves, etc.

Calculation setup

Select value to calculate. You should enter not selected one.
pressure drop
q / ṁ
volume/mass flow rate
internal pipe diameter
Select value to input. You should enter selected one. The other one will be calculated
pressure on the pipe start
pressure on the pipe end
Select value to input. You should enter selected one. The other one will be calculated
volumetric flow rate
mass flow rate
Select value to input. You should enter selected one. The other one will be calculated
kinematic viscosity
dynamic viscosity
Select pipe shape
round pipe
full cross section fluid flow
rectangle pipe
for rectangle channels and full cross section flow

When is this calculator applicable?

You can use pressure drop in pipe calculator for pressure drop and flow rate calculation for all Newtonian fluids (gases and liquids) with constant density (incompressible flow) in closed, round or rectangle pipe.

If the flowing fluid is gas, pressure change due to friction, local resistances or height change has to be low (less than 5-10%) to be sure that this calculator is applicable and that it gives correct results. If the pressure change is higher than 10%, you should use the calculator for compressible gas flow.

If you select gas as flowing fluid, the calculator assumes that gas has perfect (ideal) gas properties, i.e., the ideal gas law is applied to calculate any of the unknown gas state values - pressure, temperature or density.

Pressure drop calculator is suitable for laminar and turbulent flow regime.

Also, when it is not applicable?

You can't use this calculator for compressible gas flow where the pressure of the gas is changing more than 5-10%. For that purpose, you can use one of available gas pressure drop calculators.

You can't use this calculator if the fluid is non-Newtonian, i.e., its viscosity is changing with the shear rate or due to some other changed condition.

Pressure drop calculator is not applicable if the flowing fluid contains solid particles or if the flowing fluid is the mixture of liquid and gas, i.e., multiphase flow.

If the flowing fluid is gas but not a perfect (ideal) gas, i.e., if it's pressure, temperature and density are not related according to ideal gas law, this calculator is not applicable, also.

If the viscosity of flowing fluid is changing due to flow temperature change, this calculator is not applicable as it takes viscosity as a constant value.

Available in download version

save/open multiple results
export to word and excel
print results
custom fluid properties
K factor for fittings, resistance coefficient
pipe surface roughness selection
select between gauge and absolute pressure
compressible isothermal flow
dry air isothermal flow
gas offtake flow
natural gas flow


Calculator start selection

Read all about available deployments. In any way of utilizing calculator, Internet connection is required, for authentication at least.

Need a helping hand?


If you need a quick calculation, but you are not still familiar how to use the calculator, you can order calculation service from the calculator developer.

Order calculation service

Issues and answers

Having problems with calculators usage? Read more about known issues and problems and way to solve it.

Issues and answers

Watch how calculator can help you resolve task in less than a minute

PreDropWaterQ, D, L, kr, Δp

Example #10

Task: Calculate pressure drop in round pipe with flow of 5 m3/h, pipe length 100 m, internal pipe diameter of 25 mm and pipe roughness of 0.1 mm. Flowing fluid is water with density of 1000 kg/m3. Local resistance can be negligible K = 0.

Solution: Pressure drop is: 4.78 bar

PreDropWaterΔp, D, L, krQ

Example #11

Task: Calculate flow rate of water through closed round pipe with internal diameter of 25 mm, pipe length of 100 m. Pipe line connecting reservoir on the elevation of 20 m above the pipe exit with water flowing to open atmosphere. Reservoir is under atmospheric pressure. Pipe roughness is 0.1 mm.

Solution: Flow rate is: 3.16 m3/h

PreDropAirQ, H, W, L, krΔp

Example #12

Task: Calculate pressure drop of 2000 m3/h of air flowing through closed rectangle chanel to open atmosphere. Chanel width is 400 mm and height is 250 mm. Chanel is with surface roughness of 0.01 mm. Local resistance coefficient is line is 3.5. Chanel length is 85 m.

Solution: Pressure drop is: 298.96 Pa

Related calculators available for download