Calculator
Unit conversion
Equivalent quantities with the calculation shown below.
Equivalent values
| Unit | Value |
|---|---|
| Metres per second (m/s) | 10 |
| Kilometres per hour (km/h) | 36 |
| Miles per hour (mph) | 22.3693629205 |
| Feet per minute (ft/min) | 1,968.50393701 |
Where does the factor 3.6 come from?
A kilometre is 1000 metres and an hour is 3600 seconds. Thus 1 km/h = 1000 / 3600 m/s: divide km/h by 3.6, or multiply m/s by 3.6 for the reverse. This tool uses the international land mile for mph and the international foot for ft/min. When transferring a field reading, check whether the display’s time unit is seconds or minutes.
Air velocity and volumetric airflow need different inputs
Velocity is expressed in m/s; volumetric airflow is expressed in m³/s or m³/h. Converting velocity to flow also requires effective cross-sectional area: Q = v × A. A mean velocity of 5 m/s through 0.24 m² gives 1.2 m³/s. One point reading is not automatically the cross-sectional mean; measurement method and velocity profile affect its interpretation.
Record the measurement location and area
Fan discharge, duct and grille-face velocities may refer to different surfaces. Correct unit conversion alone does not make those values a direct performance comparison. State whether an airflow calculation uses net free area or the outside frame area. Avoid repeatedly rounding intermediate results; round the final reported value instead.
Worked examples
Convert to SI velocity
36 km/h / 3.6 = 10 m/s. Reverse check: 10 × 3.6 = 36 km/h.
Imported instrument display
1000 ft/min × 0.3048 / 60 = 5.08 m/s. Assuming seconds instead of minutes introduces a factor of sixty.
Velocity to airflow
For a mean velocity of 5 m/s and area of 0.6 × 0.4 = 0.24 m², Q = 1.2 m³/s = 4320 m³/h. The area is essential.
Definitions and calculation method
Unit factors and temperature-scale relationships: NIST SP 811, Appendix B.8 ↗.
Application examples were prepared for this page. Values are converted through the reference unit before display rounding; displayed results use up to 12 significant digits. A converted reading retains the uncertainty of the original measurement.