WaterCalculator

Water Flow Calculators

25 tools for water moving through pipes, channels and fixtures — flow rate, velocity, friction loss, pipe sizing and more. Each runs on the recognised standard formula, with the working and sources shown.

John Mac, PE Curated and reviewed by John Mac, PE, Water Systems Specialist.

Flow rate & velocity

Pipe Flow Rate CalculatorFlow rate through a pipe from diameter and velocity. GPM CalculatorGallons per minute from pipe size and pressure. Water Velocity CalculatorFlow velocity inside a pipe from flow rate and diameter. Volumetric Flow Rate CalculatorVolume of water moving past a point per unit time. Flow Rate from Pressure CalculatorFlow rate produced by a given pressure and opening size.

Friction & losses

Friction Loss CalculatorPressure lost to pipe friction over a run of pipe. Hazen-Williams CalculatorFriction loss using the Hazen-Williams formula. Darcy-Weisbach CalculatorFriction loss using the Darcy-Weisbach equation. Reynolds Number CalculatorFlow regime, laminar or turbulent, from velocity and pipe size. Equivalent Length CalculatorFitting and valve losses converted into equivalent pipe length. Minor Loss CalculatorPressure loss from bends, valves and fittings.

Pipe sizing & volume

Pipe Size CalculatorMinimum pipe diameter needed for a target flow rate. Pipe Volume CalculatorWater volume held inside a length of pipe. Pipe Water Capacity CalculatorMaximum water capacity of a pipe run. Pipe Fill Time CalculatorTime to fill a pipe or tank at a given flow rate.

Open-channel, weirs & orifices

Orifice Flow CalculatorFlow rate through a sharp-edged orifice. Weir Flow CalculatorFlow rate over a weir from head and crest length. Channel Flow CalculatorOpen-channel flow using Manning's equation. Culvert Flow CalculatorFlow capacity through a culvert. Gravity Drain Flow CalculatorFlow rate through a gravity-fed drain line.

Fixtures & hoses

Shower Flow Rate CalculatorFlow rate from a showerhead. Faucet Flow Rate CalculatorFlow rate from a kitchen or bathroom faucet. Garden Hose Flow Rate CalculatorFlow rate from a garden hose by diameter and pressure. Garden Hose Fill Time CalculatorTime to fill a pool or container with a garden hose. Hose Bib Flow Rate CalculatorFlow rate from an outdoor hose bib.

About our flow calculators

These tools model water moving through typical residential and light-commercial pipe runs, using standards such as the Hazen-Williams and Darcy-Weisbach equations for friction loss and Manning's equation for open-channel flow. Every figure is verified against the live calculator, and each page lists its sources. For the full detail of how we build and check them, see our methodology.

Browse other categories

ScienceDensity, weight, heat and properties. PressureHead, PSI, depth and losses. UsageHousehold use, footprints, savings. CostBills, rates and running costs. TreatmentSoftening, filtration, chemistry. PumpsSizing, head, horsepower, NPSH. DrainageSlopes, drain sizing, stormwater.