Pounds per Minute Calculator
Enter a mass and a time interval - or a volume flow rate and density - to calculate the mass flow rate in pounds per minute. The result is instantly converted to eight other common units: lb/hr, lb/s, kg/min, kg/hr, kg/s, g/s, oz/min, and short tons per hour. You can also start from any unit and convert back to lb/min.
What is pounds per minute?
Pounds per minute (lb/min) is a unit of mass flow rate. It tells you how many pounds of material pass through a pipe, duct, or process point in one minute. It is the standard measurement unit for mass flow in North American industrial applications including HVAC systems, chemical plants, food processing lines, and material handling conveyors. Mass flow rate is distinct from volumetric flow rate (like cubic feet per minute): mass flow accounts for the density of the substance and remains constant even when pressure or temperature change, which makes it the preferred unit for most engineering calculations.
How to calculate pounds per minute
The direct formula is: lb/min = total mass (lb) / time (min). If you know 150 lb of material moves through a system in 1 minute, the mass flow rate is 150 lb/min. If the time is in hours, multiply by 60 first; if in seconds, divide by 60. When you have a volumetric flow rate instead, multiply it by the density of the substance: lb/min = volume flow rate (ft3/min) times density (lb/ft3). For example, air at standard conditions has a density of about 0.0765 lb/ft3, so 1,000 cfm of air equals 1,000 times 0.0765 = 76.5 lb/min.
Common unit conversions and when to use them
Different industries use different preferred units. In North America, HVAC engineers typically work in lb/hr (multiply lb/min by 60), while process engineers often use lb/min directly on flow sheets. European and international specifications usually prefer kg/hr (multiply lb/min by 27.2155) or kg/s (multiply lb/min by 0.007560). Pharmaceutical and laboratory applications favor g/s (multiply lb/min by 7.5599). Mining and bulk handling often use short tons per hour (divide lb/min by 33.333). Knowing how to move between these units without errors is essential for interpreting vendor datasheets, equipment sizing, and cross-border engineering documents.
Practical applications of lb/min
Pounds per minute appears in a wide range of engineering contexts. In HVAC design, duct sizing and coil selection tables are often based on air flow in lb/min rather than CFM because mass flow is independent of air temperature and pressure. In combustion systems, fuel flow to burners is rated in lb/min, and air-to-fuel ratios use matching units. In chemical processing, reagent dosing rates and reactor feed streams are specified in lb/min or kg/hr for the same reason: mass-based accounting closes material balances regardless of process conditions. In food and pharmaceutical manufacturing, gravimetric feeders and loss-in-weight systems report output in lb/min or g/s. In firefighting, deluge and suppression system designs are based on water flow in lb/min in American codes.
Mass flow rate unit conversion quick reference
| Unit | Value | Notes |
|---|---|---|
| lb/hr | 60 | Standard for HVAC and process engineering specs |
| lb/s | 0.016667 | Used in combustion and aeronautical engineering |
| kg/min | 0.45359 | SI equivalent, common in pharmaceutical and food industries |
| kg/hr | 27.2155 | Typical for process plant flow sheets (international) |
| kg/s | 0.007560 | SI base unit for mass flow rate |
| g/s | 7.5599 | Preferred in laboratory and precision dosing |
| oz/min | 16 | Exact: 16 oz = 1 lb |
| ton/hr (short) | 0.03 | Used in bulk material handling and mining |
| t/hr (metric) | 0.027216 | International bulk transport and process plants |
1 lb/min equals the values in each row below.
Frequently asked questions
How do I convert lb/min to kg/hr?
Multiply the lb/min value by 27.2155. This combines two steps: converting pounds to kilograms (multiply by 0.45359) and converting minutes to hours (multiply by 60). For example, 10 lb/min equals 10 times 27.2155 = 272.155 kg/hr.
How do I convert CFM (cubic feet per minute) to lb/min?
Multiply the CFM value by the density of the gas or liquid in lb/ft3. For standard air at 68 F (20 C) and sea level, the density is about 0.0765 lb/ft3, so 1,000 CFM of air equals 1,000 x 0.0765 = 76.5 lb/min. The density changes with temperature and pressure, so always use the value at your actual operating conditions.
What is the difference between mass flow rate and volumetric flow rate?
Mass flow rate (lb/min, kg/s) measures how many units of mass pass a point per unit time. Volumetric flow rate (CFM, L/min, GPM) measures the volume of material instead. For liquids, the two are related by density, which barely changes with conditions. For gases, density varies significantly with temperature and pressure, so mass flow rate is often the more reliable basis for engineering calculations.
How do I convert lb/min to gallons per minute (GPM)?
Divide lb/min by the density of the liquid in lb/gal. Water weighs about 8.34 lb/gal at room temperature, so 100 lb/min of water equals 100 divided by 8.34 = approximately 11.99 GPM. For other liquids, use their specific gravity times 8.34 to get density in lb/gal.
Is lb/min used for gas flow or liquid flow?
Both. Any substance with mass can be expressed as a mass flow rate. For gases, lb/min is especially useful because it stays constant when the gas is compressed or heated (unlike volumetric measures, which change). For liquids, lb/min is common in food processing, chemical dosing, and hydraulic systems. The formula is the same in both cases: mass divided by time.
How do I convert g/s (grams per second) to lb/min?
Divide by 7.5599. Equivalently, multiply by 60 to get g/min, then divide by 453.592 to convert grams to pounds. For example, 50 g/s equals 50 divided by 7.5599 = approximately 6.61 lb/min.