Convert mass flux density between kg/(s·m²), g/(s·m²) and imperial units.
Fluids • 5 units
All 5 units on the Mass Flux Density Converter are defined against the Kilogram/(s·m²) (kg/(s·m²)), so each result is one conversion factor away from a single reference rather than the end of a chain of roundings.
The conversion this page is most often opened for is ready before you type anything: 1 kg/(s·m²) = 0.204816128 lb/(s·ft²). Change either side and every row in the table recalculates with it.
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The default conversion, 1 kg/(s·m²) into about 0.2048 lb/(s·ft²), is the bridge between process modelling and American equipment data. Two widely used flux units are deliberately absent from the table because they fold time into a different base: membrane work reports litres per square metre per hour, where 1 LMH is 2.778 × 10⁻⁴ kg/(s·m²) for water, and US practice uses gallons per square foot per day, where 1 gfd is about 1.70 LMH.
The reason this quantity is specified rather than total flow is that behaviour scales with it, not with throughput. In tubular heat exchangers the mass velocity through the tubes is what enters the Reynolds number, and the standard correlations put heat transfer proportional to roughly the 0.8 power of it. Doubling the mass flux therefore improves heat transfer by about 74% while pressure drop rises roughly fourfold — the trade-off that decides tube count and pass arrangement on almost every exchanger datasheet.
In separation processes the same number sets service life rather than performance. Filtration and membrane elements are rated at a design flux, and pushing the same throughput through a smaller area raises the flux proportionally, driving faster fouling and more frequent cleaning. This is why an undersized membrane skid appears to work perfectly on commissioning day and degrades within months: the flow figure on the datasheet was met, and the flux figure behind it was not.
Quick reference — 1 Kilogram/(s·m²) (kg/(s·m²)) is equal to:
| Gram/(s·m²) | g/(s·m²) | 1,000 |
| Kilogram/(h·m²) | kg/(h·m²) | 3,599.997120 |
| Pound/(s·ft²) | lb/(s·ft²) | 0.204816128 |
| Pound/(h·ft²) | lb/(h·ft²) | 737.338062 |
5 units of mass flux density, each a fixed multiple of the kg/(s·m²). The table spans 17,577:1, from kg/(h·m²) (0.000277778 kg/(s·m²)) to lb/(s·ft²) (4.88243 kg/(s·m²)). Conversion is one multiplication into the base unit and one division out of it, with no lookup table and no approximation.
value_to = value_from × (factor_from ÷ factor_to)1 kg/(s·m²) = 1 kg/(s·m²)1 g/(s·m²) = 0.001 kg/(s·m²)1 kg/(h·m²) = 0.000277778 kg/(s·m²)1 lb/(s·ft²) = 4.88243 kg/(s·m²)1 lb/(h·ft²) = 0.00135623 kg/(s·m²)where:
Assumptions: Factors are exact definitions. Full double precision is carried internally and rounding is applied only for display.
Result25 kg/(s·m²) = 5.1204 lb/(s·ft²)
Mass flux density is mass flow rate divided by the area it crosses, in kg/(s·m²). Where mass flow rate tells you how much is moving, mass flux tells you how hard it is being pushed through a given opening.
This is the quantity that sizes membranes and filters. A reverse-osmosis membrane is rated by flux, so doubling the area at the same flux doubles the throughput, while pushing the same throughput through half the area doubles the flux and shortens the element's life. It also governs drying, evaporation and packed-bed reactors, where the same total flow behaves very differently depending on the cross-section it is forced through.