Convert lb/hr to US GPM or US GPM to lb/hr using an editable fluid density, with illustrative presets, custom specific gravity, L/min, m³/hr, and kg/hr.
- All Unit Converters
- GPM to Pipe Size Calculator
- GPM (gallons/min) Calculator
- Cubic Feet to Pounds Calculator
- Cubic Feet to Tons Calculator
- Casing Capacity (Annular Volume) Calculator
- Annular Velocity Calculator
- Oil Velocity Calculator
Watch the full explanation and transcript.
| LB/hr to GPM | GPM to LB/hr |
|---|---|
| 100 lb/hr = 0.200 GPM | 0.1 GPM = 50.1 lb/hr |
| 250 lb/hr = 0.499 GPM | 0.25 GPM = 125.2 lb/hr |
| 500 lb/hr = 0.999 GPM | 0.5 GPM = 250.4 lb/hr |
| 750 lb/hr = 1.498 GPM | 0.75 GPM = 375.5 lb/hr |
| 1,000 lb/hr = 1.997 GPM | 1 GPM = 500.7 lb/hr |
| 1,500 lb/hr = 2.996 GPM | 2 GPM = 1,001.4 lb/hr |
| 2,000 lb/hr = 3.994 GPM | 5 GPM = 2,503.5 lb/hr |
| 3,000 lb/hr = 5.992 GPM | 10 GPM = 5,007 lb/hr |
| 5,000 lb/hr = 9.986 GPM | 20 GPM = 10,014 lb/hr |
| 7,500 lb/hr = 14.979 GPM | 50 GPM = 25,035 lb/hr |
| Formulas: lb/hr = GPM x density(lb/gal) x 60 and GPM = lb/hr / (density x 60). This table assumes water density = 8.345 lb/gal. | |
| kg/hr to L/min | L/min to kg/hr |
|---|---|
| 30 kg/hr = 0.500 L/min | 0.5 L/min = 30 kg/hr |
| 60 kg/hr = 1.000 L/min | 1 L/min = 60 kg/hr |
| 90 kg/hr = 1.500 L/min | 2 L/min = 120 kg/hr |
| 120 kg/hr = 2.000 L/min | 3 L/min = 180 kg/hr |
| 180 kg/hr = 3.000 L/min | 5 L/min = 300 kg/hr |
| 300 kg/hr = 5.000 L/min | 10 L/min = 600 kg/hr |
| 600 kg/hr = 10.000 L/min | 15 L/min = 900 kg/hr |
| 900 kg/hr = 15.000 L/min | 20 L/min = 1,200 kg/hr |
| 1,200 kg/hr = 20.000 L/min | 50 L/min = 3,000 kg/hr |
| 3,000 kg/hr = 50.000 L/min | 100 L/min = 6,000 kg/hr |
| Formulas: kg/hr = (L/min) x density(kg/L) x 60 and L/min = kg/hr / (density x 60). Water density = 1.000 kg/L. | |
LB/Hr to GPM Formula
The core formula converts a mass flow rate into a volumetric flow rate by dividing out the fluid’s density and adjusting the time base from hours to minutes:
- Where GPM is the gallons per minute (volumetric flow rate)
- lb/hr is the mass flow rate in pounds per hour
- D is the density of the fluid in lb/gallon (for water at 60 °F, D = 8.337 lb/gal)
The division by density converts mass to volume (lb divided by lb/gal yields gallons), and the division by 60 converts per-hour to per-minute. This is the standard relationship between mass flow and volumetric flow for any incompressible liquid.
Why Mass Flow and Volumetric Flow Differ
Mass flow (lb/hr) and volumetric flow (GPM) measure fundamentally different physical quantities. Mass flow tracks how much matter passes a point per unit time, while volumetric flow tracks how much space that matter occupies. The bridge between them is density, which changes with temperature and fluid composition. A Coriolis meter reading 5,000 lb/hr of hot water at 200 °F produces a different GPM than the same 5,000 lb/hr at 60 °F because the water expands as it heats. This is why process engineers working with boiler feedwater, steam condensate return lines, or heated glycol loops cannot treat the conversion as a fixed ratio.
In HVAC hydronic systems, a common shorthand is that 1 GPM of water carries roughly 500 lb/hr (based on 8.33 lb/gal x 60 min). That approximation works well near 60 °F, but at 180 °F the saturated-liquid reference is about 486 lb/hr per US GPM, using approximately 8.10 lb/US gal. Acceptable design error depends on the system, but in high-temperature industrial loops or when dosing expensive chemicals, using the correct density for the actual operating temperature matters.
Water Density vs. Temperature Reference
Since water is the most common fluid in lb/hr to GPM conversions, the table below shows how water’s density in lb/gallon shifts across a typical operating range. Using the correct density at your system’s operating temperature will improve conversion accuracy, especially for boiler feed, condensate, and hot-water systems.
| Temperature (°F) | Density (lb/gal) | lb/hr per 1 GPM |
|---|---|---|
| 39.2 (max density) | 8.345 | 500.7 |
| 60 | 8.337 | 500.2 |
| 80 | 8.317 | 499.0 |
| 100 | 8.287 | 497.2 |
| 120 | 8.249 | 495.0 |
| 140 | 8.205 | 492.3 |
| 160 | 8.154 | 489.3 |
| 180 | 8.098 | 485.9 |
| 200 | 8.037 | 482.2 |
| 212 (saturated liquid) | 7.998 | 479.9 |
| 250 (pressurized) | 7.863 | 471.8 |
| lb/hr per US GPM = density (lb/US gal) × 60. At 200 °F the factor is about 3.7% below the 39 °F reference. Values are interpolated from NIST’s IAPWS-95 saturation table. Liquid water at 250 °F requires pressurization; its saturation pressure is approximately 29.85 psia. Use density at actual operating pressure. | ||
Densities of Common Industrial Fluids
The calculator defaults to an illustrative water density of 1 kg/L (approximately 8.345 lb/US gal). The table below gives illustrative assumed densities, not universal fluid specifications. Enter measured or supplier density at operating temperature, pressure and composition into the editable density field.
| Fluid | Density (lb/gal) | Typical Application |
|---|---|---|
| Fresh water | 8.34 | Cooling towers, boiler feed, HVAC |
| Seawater (3.5% salinity) | 8.56 | Desalination, offshore cooling |
| 50/50 ethylene glycol/water | 8.92 | Chilled-water loops, freeze protection |
| 50/50 propylene glycol/water | 8.72 | Food-safe freeze protection |
| Diesel fuel (#2) | 7.09 | Fuel transfer, generator feed |
| Gasoline | 6.17 | Fuel systems |
| Hydraulic oil (ISO 46) | 7.20 | Hydraulic power units |
| Crude oil (API 35) | 7.18 | Pipeline transport |
| Sulfuric acid (98%) | 15.33 | Chemical dosing |
| Sodium hydroxide (50%) | 12.63 | pH adjustment, scrubbers |
| Liquid ammonia | 5.15 | Refrigeration systems |
| Ethanol (100%) | 6.58 | Solvent, biofuel blending |
| Milk (whole) | 8.60 | Dairy processing |
| Values are illustrative assumptions. Verify temperature, pressure, composition and concentration; liquid ammonia requires suitable pressure. | ||
Where This Conversion Is Used
The lb/hr to GPM conversion is useful when mass flow is measured but volume flow is needed. A 10,000 lb/hr liquid-water stream at 180 °F corresponds to approximately 10,000 / (8.098 × 60) = 20.6 US GPM using the saturated-liquid reference. Actual boiler pump sizing also depends on condensate return, blowdown and other operating requirements.
Chemical dosing is another frequent use case. Metering pumps for water treatment chemicals such as sodium hypochlorite, coagulants, and pH adjusters are typically cataloged in GPM or gallons per hour, while dosing requirements are specified in lb/hr based on contaminant loading. Converting accurately requires knowing the exact specific gravity of the chemical solution, which varies with concentration. For a solution whose verified density is 9.58 lb/US gal, 100 lb/hr equals 100 / (9.58 x 60) = 0.174 GPM.
In oil and gas, custody transfer meters often report in mass units to eliminate the ambiguity of temperature-dependent volume. Converting the mass reading to GPM is needed when routing that fluid through volumetric equipment like positive-displacement pumps or tank level gauges calibrated in gallons. The same principle applies in food and beverage processing, pharmaceutical manufacturing, and any industry where regulatory compliance ties to mass-based measurement but operational equipment relies on volumetric sizing.
Working With Different Density Units
Not all datasheets report density in lb/gallon. If you have density in lb/ft3, divide by 7.481 to get lb/gal (since 1 ft3 = 7.481 gallons). If you have specific gravity (SG), multiply by 8.345 to get lb/gal (since SG is the ratio of the fluid’s density to water’s density at 4 °C, and water at 4 °C is 8.345 lb/gal). If your density is in kg/m3, divide by 119.83 to get lb/gal, or multiply by 0.001 to get kg/L and use the calculator’s metric mode. These conversions ensure you can enter any published density into the formula without hunting for a separate unit converter.
FAQ
What is the quick rule of thumb for water?
For water near 60 °F, 1 GPM equals approximately 500 lb/hr. This comes from 8.34 lb/gal multiplied by 60 minutes. It is accurate to within about 1% for water between 40 °F and 100 °F, but deviates more at elevated temperatures (see the temperature table above).
Does this formula work for gases?
The mass-flow divided by density relationship also gives actual gas volume flow if density is known at the same temperature and pressure. This calculator does not infer gas density or convert to standard gas volume. SCFM requires specified reference conditions and appropriate gas properties.
How do I convert if my density is in lb/ft3 instead of lb/gal?
Divide the lb/ft3 value by 7.481 to get lb/gal (since 1 cubic foot equals 7.481 US gallons). For example, water at 60 °F has a density of about 62.37 lb/ft3, and 62.37 / 7.481 = 8.337 lb/gal.
Why does the HVAC industry use 500 lb/hr per GPM?
Hydronic HVAC calculations assume water near 60 °F, where the density is roughly 8.33 lb/gal. Multiplying by 60 minutes gives 499.8, which rounds to 500. This simplification makes it easy to estimate pump flow from a BTU load: GPM = BTU/hr / (500 x delta-T in °F). The heat-load factor also assumes water’s specific heat near 1 Btu/(lb·°F): it is 60 × density × specific heat. Verify fluid properties and design requirements at operating conditions.
How much error does temperature introduce?
Using the saturated-liquid references above, density falls from 8.337 lb/US gal at 60 °F to 7.998 at 212 °F, about 4.1%. Using the 60 °F density therefore understates actual volume flow by about 4.1%. At 250 °F the difference is about 5.7%. Actual error depends on operating pressure, and acceptable design margins must be assessed for the system.
