Mass Flow Rate Converter
Mass flow rate is the mass passing a point per unit time, with the SI unit of kilograms per second (kg/s). Process and HVAC engineers also use kilograms per hour, grams per second, pounds per second or hour, and metric tonnes per hour. This converter reduces any of these to kilograms per second as a base and converts out, using exact factors: 1 hour equals 3,600 s, 1 pound equals 0.45359237 kg exactly, and 1 metric tonne equals 1,000 kg.
Mass flow rate conversion
Base value (kg/s) = input * factor(from unit)
Output = base value / factor(to unit)
1 kg/h = 1/3600 kg/s
1 lb/s = 0.45359237 kg/s
1 t/h = 1000/3600 kg/s
The pound is the international avoirdupois pound, exactly 0.45359237 kg. The metric tonne is 1,000 kg.
Mass flow rate context
- The SI unit of mass flow rate is the kilogram per second (kg/s).
- The international avoirdupois pound is exactly 0.45359237 kg.
- Mass flow rate equals density times volumetric flow rate times area, or density times volume flow.
- A metric tonne is 1,000 kg; tonnes per hour is common in bulk material handling.
- Dividing a per-hour rate by 3,600 gives the per-second rate.
Mass flow rate: frequently asked questions
What is the SI unit of mass flow rate?
The kilogram per second (kg/s). All other units, such as kg/h, lb/s, or tonne/h, convert to it through exact mass and time factors.
How do I convert kg/h to kg/s?
Divide by 3,600, since there are 3,600 seconds in an hour. So 3,600 kg/h equals 1 kg/s.
What pound is used?
The international avoirdupois pound, defined as exactly 0.45359237 kilogram. The converter uses this value for all pound-based flow rates.
Is mass flow the same as volume flow?
No. Mass flow rate measures mass per time (kg/s); volumetric flow rate measures volume per time (m3/s). They are related by the fluid density, which varies with temperature and pressure.
How is tonne per hour converted?
A metric tonne is 1,000 kg and an hour is 3,600 s, so 1 t/h equals 1,000 divided by 3,600 kg/s, about 0.2778 kg/s.
Official sources
- NIST Special Publication 811: Guide for the Use of the International System of Units.
- BIPM: SI Units.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.