Estimate flow in seconds with trusted physics equations. Switch between area, volume, and pipe modes easily. Download clean results for reports anytime.
| Scenario | Inputs | Expected output |
|---|---|---|
| Rectangular duct | A = 0.020 m², v = 2.0 m/s | Q = 0.040 m³/s (40 L/s) |
| Bucket test | V = 15 L, t = 30 s | Q = 0.0005 m³/s (0.5 L/s) |
| Pipe line | d = 50 mm, v = 1.5 m/s | Q ≈ 0.00295 m³/s (2.95 L/s) |
| Mass flow (water) | Q = 0.00295 m³/s, ρ = 998 kg/m³ | ṁ ≈ 2.95 kg/s |
Numbers are rounded for readability.
Flow rate links geometry and motion. Volumetric flow rate Q is measured in m³/s, L/s, m³/h, or US gpm. In real ducts and pipes the velocity profile is not flat, so the calculator assumes a representative mean velocity. For quick checks, take several readings across the section and average them before computing Q. For liquids, Reynolds number Re = ρvd/μ indicates laminar versus turbulent regimes; turbulent flow typically needs larger safety margins when comparing calculated Q to pump curves and valve ratings in practical field troubleshooting work.
Use Area × Velocity when the cross section is known and velocity comes from a vane anemometer, pitot tube, or ultrasonic meter. Use Volume ÷ Time for bucket tests, tank fills, or calibration runs where volume is captured directly. Pipe mode is useful when only inner diameter is available; it derives area with A = πd²/4, then multiplies by velocity.
Reference ranges help you spot unit mistakes. A household faucet is often 5–12 L/min, a shower head 6–15 L/min, and a garden hose 15–30 L/min. Small lab pumps commonly operate near 0.5–3 L/s. Building circulation lines can exceed 50–200 L/s depending on pipe size, head, and control valve position. Industrial transfer pumps may run in the 10–500 m³/h range.
When density is known, mass flow ṁ = ρQ supports energy and process calculations. Water near 20–25 °C is about 998 kg/m³, sea water is roughly 1025 kg/m³, and air at standard conditions is about 1.2 kg/m³. Mass flow connects to heating and cooling by ṁcpΔT, and to chemical dosing by multiplying ṁ by mass fraction. The calculator converts density units to keep results consistent.
Uncertainty is often dominated by sensor placement, turbulence, and timing. If the time interval is short, a 0.5 s stopwatch error can noticeably change Q. Prefer longer collection times, stable flow, and documented units. Exported CSV files fit spreadsheets for trending, while the PDF snapshot is convenient for lab notebooks, commissioning reports, and client handovers.
Velocity describes how fast fluid moves at a point. Flow rate describes how much volume passes per time. They connect through Q = A×v, using the cross-sectional area.
Choose Volume ÷ Time. Measure the collected volume and the filling time, then calculate Q. Use longer times to reduce stopwatch error.
Use inner diameter, because flow area is based on the internal cross section. If you only have nominal sizes, check the pipe schedule or manufacturer data for the true inner diameter.
Compute mass flow when energy, mixing, or dosing depends on kilograms per second. Provide density and enable the mass-flow option, which applies ṁ = ρQ automatically.
Pump curves depend on head, viscosity, fittings, and valve position. Measurement location and turbulence also matter. Use the calculator for steady-state estimates, then compare with in-system readings and curve points.
Exports include the displayed units: m³/s, L/s, m³/h, and US gpm, plus any derived area, velocity, and mass flow. The export reflects the most recent calculation shown above the form.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.