Fluid Mechanics Calculators
These calculators cover liquids and gases moving through pipes, pumps and tanks: converting between flow rate, velocity and pipe size, finding the Reynolds number and whether flow is laminar or turbulent, calculating friction losses with the Darcy-Weisbach equation, sizing a pump's power, applying Bernoulli's equation, finding pressure at depth, working out how much a partly filled tank holds and estimating flow through an orifice.
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All Fluid Mechanics (8)
Flow Rate Calculator
Volumetric flow rate, velocity and pipe area conversionsReynolds Number Calculator
Reynolds number and flow regime for pipe flowPipe Pressure Drop Calculator
Friction loss in pipes with Darcy-Weisbach and the Colebrook equationPump Power Calculator
Hydraulic and shaft power from flow, head and efficiencyBernoulli Equation Calculator
Solve Bernoulli's equation for pressure, velocity or heightHydrostatic Pressure Calculator
Pressure at depth in a fluid and force on a submerged surfaceTank Volume Calculator
Total and filled volume of cylindrical, rectangular and spherical tanksOrifice Flow Calculator
Flow through an orifice or nozzle from pressure drop
Which tool do I need?
Find the pressure loss in a water pipe
Enter the flow, pipe diameter, length and material to get the friction factor, velocity and pressure drop.
Size the motor for a pump
Enter the flow, total head and efficiencies to get the hydraulic, shaft and motor power.
Measure how much is left in a horizontal tank
Enter the tank size and the liquid depth to get the filled volume and percentage.
Check the water pressure at the bottom of a tank
Enter the depth and fluid to get the gauge and absolute pressure.
About Fluid Mechanics
Pressure drop uses the Colebrook-White equation for the friction factor with typical pipe roughness values, and fluid presets cover water at common temperatures and other fluids with their density and viscosity, all editable.
The models assume steady, incompressible flow of a Newtonian fluid unless noted. Gases at high velocity, two-phase flow and long networks with many fittings need more detailed analysis.
Guides
- Pipe Flow Rate, Velocity and Diameter: Using Q = vA ProperlyContinuity in one line, the unit factors that trip people up, design velocity ranges for water, and how to size a pipe bore from a flow without fooling yourself.
- Reynolds Number Explained: Laminar, Transitional and Turbulent FlowWhat Re = ρvD/μ measures, where the 2300 and 4000 limits come from, how temperature changes viscosity, and how to use hydraulic diameter for ducts and annuli.
- Darcy-Weisbach and the Colebrook Equation: Pipe Friction Loss in PracticeWhere the friction factor comes from, how to solve Colebrook and when Swamee-Jain is good enough, typical roughness and K values, and a full worked pressure drop.
- Pump Power, Head and Efficiency: From ρgQH to the Electricity BillHydraulic, brake and motor power, why head is not pressure, picking a motor that survives run-out, yearly energy cost and how NPSH available is worked out.
Frequently asked questions
At what Reynolds number does pipe flow become turbulent?
Flow is usually laminar below about 2,300 and turbulent above about 4,000, with a transition region in between where the behaviour is unpredictable.
Why use Darcy-Weisbach rather than Hazen-Williams?
Darcy-Weisbach works for any fluid, temperature and flow regime and is based on physics. Hazen-Williams is an empirical shortcut for water at ordinary temperatures in turbulent flow.
Which pressure do the fluid calculators report, gauge or absolute?
Gauge pressure is measured relative to the surrounding atmosphere, absolute pressure relative to a vacuum. Absolute equals gauge plus about 101.3 kPa at sea level.
How do I convert between GPM and litres per second?
One US gallon per minute is about 0.0631 litres per second, and one litre per second is about 15.85 US gallons per minute. The flow rate calculator converts every unit at once.