Mass flow rate is a critical parameter in process engineering, representing the mass of a substance passing through a given cross-section per unit of time. The pound per hour (lb/h) is a common unit in the US Customary system, frequently utilized in industrial steam systems, HVAC, and chemical processing. Conversely, the kilogram per second (kg/s) is the SI derived unit, preferred in scientific research and international engineering standards.
lb/h: Measures the mass of fluid in pounds flowing past a point in one hour.
kg/s: Measures the mass of fluid in kilograms flowing past a point in one second.
To convert between these units, we must account for the mass conversion (1 lb \(\approx\) 0.453592 kg) and the time conversion (1 hour = 3600 seconds). The resulting conversion factor is \(1 \text{ lb/h} \approx 0.000125997881 \text{ kg/s}\).
Pound per hour to Kilogram per second Conversion Reference Table
Pound per hour (lb/h)
Kilogram per second (kg/s)
0.1
1.2600e-05
0.5
6.2999e-05
1.0
1.2600e-04
2.0
2.5200e-04
5.0
6.2999e-04
10.0
0.0013
20.0
0.0025
50.0
0.0063
100.0
0.0126
500.0
0.063
1000.0
0.126
Conversion Example: 10 lb/h to kg/s
To convert a mass flow rate of 10 lb/h into kg/s, multiply the value by the conversion factor:
The factor is small because you are converting from a larger time unit (hour) to a much smaller one (second), while simultaneously converting from pounds to kilograms. Since one hour contains 3,600 seconds, the flow rate per second is significantly lower than the flow rate per hour.
You should use kg/s when working with SI-based engineering calculations, international project specifications, or scientific modeling where standard units are required to ensure compatibility with other physical constants.
"On fait la science avec des faits, comme on fait une maison avec des pierres ; mais une accumulation de faits n'est pas plus une science qu'un tas de pierres n'est une maison." "Science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house." — Henri Poincaré (French Mathematician, Theoretical Physicist & Mining Engineer)