Understanding mass flow rate
Mass flow answers “how much stuff per second,” not how much space it occupies. Fuel burn, steam export, and ingredient feeds on a batch plant all land here. We normalize every choice to kilograms per second so you can hop from grams per minute to short tons per hour without inventing new algebra each time.
How mass flow conversion works
Each unit carries an implicit “per second” after you unfold minutes, hours, or days. You convert your reading to kg/s with the source row, then divide by the target row to land in the unit your report expects.
Result = Value × (source as kg/s per unit) ÷ (target as kg/s per unit)
Quick mental check: one pound per second is a little under half a kilogram per second (0.453592 kg). If your answer drifts far from that ballpark, recheck whether you grabbed per day instead of per hour.
Conversion factors: units worth knowing
The long tail of SI prefixes is for rare edge cases. These are the ones people actually argue about in meetings.
Kilogram per second [kg/s]
Factor: 1 (base)
The clean SI rate. Works well with reactor balances where everything else is already kg or mol.
Gram per minute [g/min]
Factor: grams per minute expressed as kg/s
Small dosing pumps and lab rotameters often quote this. Remember that “per minute” adds a factor of 60 in the denominator compared to per second.
Pound per hour [lb/h]
Factor: avoirdupois pound to kg, spread over an hour
Classic US boiler and burner language. One pound is exactly 0.45359237 kg by modern definition.
Metric ton per day [t/d]
Factor: 1000 kg per metric tonne, per calendar day length in seconds
Ship loading, cement plants, grain terminals. “Ton” here means metric tonne unless your contract snaps to short tons.
Short ton (US) per hour
Factor: 2000 lb per short ton
Used in North American bulk industries. If someone says “ton per hour” near a coal pile, confirm short versus metric before you scale the motor.
Megagram per second [Mg/s]
Factor: 1000 kg/s per Mg/s
A megagram is a tonne by another name. Same mass as a metric ton, just dressed in SI prefixes.
Common mass flow conversions at a glance
Handy anchors when you do not have a calculator in your pocket (you do now, but humor the field tech).
| From | To | Pattern | Example |
|---|---|---|---|
| kg/h | kg/s | ÷ 3600 | 3600 kg/h = 1 kg/s |
| lb/h | kg/h | × 0.453592 | 10 lb/h ≈ 4.54 kg/h |
| g/min | kg/s | ÷ 60 000 | 600 g/min = 0.01 kg/s |
| t/d | kg/s | 1000 ÷ 86400 | 86.4 t/d = 1 kg/s |
| kg/s | lb/s | ÷ 0.453592 | 1 kg/s ≈ 2.205 lb/s |
| Mg/s | kg/s | × 1000 | 0.001 Mg/s = 1 kg/s |
When mass flow beats volumetric flow
Compressible gases change density with pressure and temperature, so a cubic meter per hour is a moving target. Mass flow stays honest: a kilogram is a kilogram whether the fluid is squished or not. For liquids, density is usually stable enough that either rate works, but custody transfer often still prefers mass for accounting.
If you need to jump between mass flow and volume flow, grab a density at the conditions you care about and apply it consistently. Mixing STP density with line temperature without saying so is how innocent spreadsheets grow teeth.
Mass flow FAQ
What is a short ton versus a metric ton?
A short ton is 2000 pounds (common in the US). A metric ton (tonne) is 1000 kg. Our “short ton per hour” row tracks the US definition only.
How do I convert kg/h to lb/h?
Convert each unit to kg/s first, or multiply kg/h by 2.20462 to get lb/h directly. This tool handles both routes without you memorizing constants.
Why so many prefixes on gram per second?
Some datasheets quote exotics for reactor scale or trace feeds. They are rare in everyday maintenance, but when they show up you want them without building a second spreadsheet.
Does a day mean exactly 24 hours?
Yes for these rows: a day is 86,400 seconds. Leap seconds do not touch kitchen-table conversion math.