What this site is
Most online calculators give you a number and nothing else. That is fine for a quick check, but it does not help you learn the method or spot a mistake. Every calculator here shows the formula, the substitution and the arithmetic, and every page includes worked examples you can load with one click.
The tools are built by a chemical engineering student for students and early-career engineers working through fluid flow, pumping and heat transfer. They are free, need no signup, and run entirely in your browser.
The six calculators
Reynolds Number Calculator
Find Re and the flow regime (laminar, transitional or turbulent) from density, velocity, diameter and viscosity. Works with dynamic or kinematic viscosity.
Start here for any pipe-flow problem.
Open calculator
Friction Factor and Head Loss Calculator
Darcy-Weisbach head loss for a straight pipe, using 64/Re for laminar flow and the Swamee-Jain equation for turbulent flow.
Use it once you know Re and want the pressure drop.
Open calculator
Pump Power Calculator
Hydraulic and brake power from flow rate and either head or pressure rise, so you can pick a motor.
Use it when you know the duty and need a driver size.
Open calculator
NPSH Calculator
Net positive suction head available, with a cavitation check against the pump's required NPSH.
Use it before you commit to a pump.
Open calculator
LMTD Calculator
Log mean temperature difference for counter-current or co-current heat exchangers, including the equal-difference edge case.
Start here for any heat exchanger problem.
Open calculator
Heat Exchanger Area Calculator
Required heat transfer area from duty, overall coefficient and LMTD, with the option to calculate LMTD from temperatures.
Use it to size the surface once you have Q, U and LMTD.
Open calculator
Two suggested learning paths
Piping and pumping: Reynolds number → friction factor and head loss → pump power → NPSH. Each result feeds the next: Re tells you the flow regime, which gives the friction factor, which gives the head the pump must develop, which sets the power and the suction requirement.
Heat transfer: LMTD → heat exchanger area. The temperature difference from the first tool is the driving force in the second.
Assumptions and accuracy
All calculators use SI units and g = 9.81 m/s². Head loss uses the Darcy friction factor, with 64/Re for laminar flow and the Swamee-Jain approximation of the Colebrook-White equation for turbulent flow. Results between Re 2,300 and 5,000 are estimates, because real flow in that band is unpredictable. The heat exchanger tools assume pure counter-current or co-current flow (correction factor F = 1). These calculators are for learning, checking and preliminary estimates. They are not a substitute for a full design or for the checks your project standards require.
Frequently Asked Questions
Are these calculators really free?
Yes. There is no signup and no paywall. The site may show ads later to cover the time it takes to build and maintain it.
Can I use them in an exam?
Check your exam rules. Most closed-book exams do not allow websites. They are best used to check your practice problems and to see where a hand calculation went wrong.
Which units do the calculators use?
SI units throughout: metres, seconds, kilograms, pascals and degrees Celsius for temperature differences. Each input box shows the unit it expects.
I think I found an error. What should I do?
Please tell me on the Contact page, and include the calculator, the values you entered and the result you expected. Corrections are made quickly.