Flow Rate Converter
Flow Rate Converter — From L/s to CFM, GPM, kg/h & More
Convert flow rates across 51 units in 5 categories: volume flow (L/s, gal/min, CFM), mass flow (kg/s, lb/h), and specialized units (barrel/day, MGD). Includes water density considerations for mass-volume conversions.
Foundations of Flow Rate
Volume Flow Rate
Volume of fluid per time. Units: L/s, m3/h, gal/min, CFM (ft3/min). Most common for pumps, pipes, HVAC. Independent of fluid type within volume measurement.
- L/s: metric standard
- gal/min (GPM): US plumbing
- CFM: HVAC airflow
- m3/h: large systems
Mass Flow Rate
Mass of fluid per time. Units: kg/s, lb/h, t/day. Used in chemical processes. Converting to volume REQUIRES knowing density! Water = 1 kg/L, oil = 0.87 kg/L, different!
- kg/s: SI mass flow
- lb/h: US industrial
- Needs density for volume!
- Water assumption common
Volume vs Mass Flow
Mass flow = Volume flow x Density. 1 kg/s water = 1 L/s (density 1 kg/L). Same 1 kg/s oil = 1.15 L/s (density 0.87 kg/L). Always check density when converting!
- m = ρ x V (mass = density x volume)
- Water: 1 kg/L assumed
- Oil: 0.87 kg/L
- Air: 0.0012 kg/L!
- Volume flow: L/s, gal/min, CFM (m3/min)
- Mass flow: kg/s, lb/h, t/day
- Related by density: m = ρ × V
- Water density = 1 kg/L (assumed for conversions)
- Other fluids: multiply by density ratio
- Always specify fluid type for accuracy!
Flow Rate Systems
Metric Volume Flow
SI units worldwide. Liter per second (L/s) base unit. Cubic meter per hour (m3/h) for large systems. Milliliter per minute (mL/min) for medical/lab.
- L/s: standard flow
- m3/h: industrial
- mL/min: medical
- cm3/s: small volumes
US Volume Flow
US customary units. Gallons per minute (GPM) in plumbing. Cubic feet per minute (CFM) in HVAC. Fluid ounce per hour for small flows.
- GPM: plumbing standard
- CFM: airflow (HVAC)
- ft3/h: gas flow
- fl oz/min: dispensing
Mass Flow & Specialized
Mass flow: kg/s, lb/h for chemical plants. Barrel per day (bbl/day) for oil. MGD (million gallons per day) for water treatment. Acre-foot per day for irrigation.
- kg/h: chemical industry
- bbl/day: oil production
- MGD: water plants
- acre-ft/day: irrigation
The Physics of Flow
Continuity Equation
Flow rate constant in pipe: Q = A x v (flow = area x velocity). Narrow pipe = faster flow. Wide pipe = slower flow. Same volume passes through!
- Q = A × v
- Smaller area = higher velocity
- Volume conserved
- Incompressible fluids
Density & Temperature
Density changes with temperature! Water at 4C: 1.000 kg/L. At 80C: 0.972 kg/L. Affects mass-volume conversion. Always specify conditions!
- ρ varies with T
- Water density peaks at 4C
- Hot fluids less dense
- Specify temperature!
Compressible Flow
Gases compress, liquids don't. Air flow needs pressure/temperature correction. Standard conditions: 1 atm, 20C. Volumetric flow changes with pressure!
- Gases: compressible
- Liquids: incompressible
- STP: 1 atm, 20C
- Correct for pressure!
Common Flow Rate Benchmarks
| Application | Typical Flow | Notes |
|---|---|---|
| Garden hose | 15-25 L/min (4-7 GPM) | Residential watering |
| Shower head | 8-10 L/min (2-2.5 GPM) | Standard flow |
| Kitchen faucet | 6-8 L/min (1.5-2 GPM) | Modern low-flow |
| Fire hydrant | 3,800-5,700 L/min (1000-1500 GPM) | Municipal supply |
| Car radiator | 38-76 L/min (10-20 GPM) | Cooling system |
| IV drip (medical) | 20-100 mL/h | Patient hydration |
| Small aquarium pump | 200-400 L/h (50-100 GPH) | Fish tank circulation |
| Home AC unit | 1,200-2,000 CFM | 3-5 ton system |
| Industrial pump | 100-1000 m3/h | Large-scale transfer |
Real-World Applications
HVAC & Plumbing
HVAC: CFM (cubic feet per minute) for airflow. Typical home: 400 CFM per ton AC. Plumbing: GPM for water flow. Shower: 2-2.5 GPM. Kitchen faucet: 1.5-2 GPM.
- AC: 400 CFM/ton
- Shower: 2-2.5 GPM
- Faucet: 1.5-2 GPM
- Toilet: 1.6 GPF
Oil & Gas Industry
Oil production measured in barrels per day (bbl/day). 1 barrel = 42 US gallons = 159 liters. Pipelines: m3/h. Natural gas: standard cubic feet per day (scfd).
- Oil: bbl/day
- 1 bbl = 42 gal = 159 L
- Pipeline: m3/h
- Gas: scfd
Chemical & Medical
Chemical plants: kg/h or t/day mass flow. IV drips: mL/h (medical). Lab pumps: mL/min. Mass flow critical for reactions - need exact amounts!
- Chemical: kg/h, t/day
- IV drip: mL/h
- Lab pump: mL/min
- Mass critical!
Quick Math
GPM to L/min
1 gallon (US) = 3.785 liters. Quick: GPM x 3.8 ≈ L/min. Or: GPM x 4 for rough estimate. 10 GPM ≈ 38 L/min.
- 1 GPM = 3.785 L/min
- GPM x 4 ≈ L/min (quick)
- 10 GPM = 37.85 L/min
- Easy conversion!
CFM to m3/h
1 CFM = 1.699 m3/h. Quick: CFM x 1.7 ≈ m3/h. Or: CFM x 2 for rough estimate. 1000 CFM ≈ 1700 m3/h.
- 1 CFM = 1.699 m3/h
- CFM x 2 ≈ m3/h (quick)
- 1000 CFM = 1699 m3/h
- HVAC standard
Mass to Volume (Water)
Water: 1 kg = 1 L (at 4C). So 1 kg/s = 1 L/s. Quick: kg/h = L/h for water. Other fluids: divide by density!
- Water: 1 kg = 1 L
- kg/s = L/s (water only)
- Oil: divide by 0.87
- Gasoline: divide by 0.75
How Conversions Work
- Step 1: Identify flow type (volume or mass)
- Step 2: Convert within same type normally
- Step 3: Mass to volume? Need density!
- Step 4: Water assumed if not specified
- Step 5: Other fluids: apply density correction
Common Conversions
| From | To | Factor | Example |
|---|---|---|---|
| L/s | L/min | 60 | 1 L/s = 60 L/min |
| L/min | GPM | 0.264 | 10 L/min = 2.64 GPM |
| GPM | L/min | 3.785 | 5 GPM = 18.9 L/min |
| CFM | m3/h | 1.699 | 100 CFM = 170 m3/h |
| m3/h | CFM | 0.589 | 100 m3/h = 58.9 CFM |
| m3/h | L/s | 0.278 | 100 m3/h = 27.8 L/s |
| kg/s | L/s | 1 (water) | 1 kg/s = 1 L/s (water) |
| lb/h | kg/h | 0.454 | 100 lb/h = 45.4 kg/h |
Quick Examples
Worked Problems
Pump Sizing
Need to fill 1000 gallon tank in 10 minutes. What pump flow rate in GPM?
Flow = Volume / Time = 1000 gal / 10 min = 100 GPM. In metric: 100 GPM x 3.785 = 378.5 L/min = 6.3 L/s. Choose pump rated ≥100 GPM.
HVAC Airflow
Room is 20ft x 15ft x 8ft. Need 6 air changes per hour. What CFM?
Volume = 20 x 15 x 8 = 2400 ft3. Changes/hour = 6, so 2400 x 6 = 14,400 ft3/hour. Convert to CFM: 14,400 / 60 = 240 CFM needed.
Mass Flow Conversion
Chemical plant: 500 kg/h of oil (density 0.87 kg/L). What is volume flow in L/h?
Volume = Mass / Density = 500 kg/h / 0.87 kg/L = 575 L/h. If this was water (1 kg/L), would be 500 L/h. Oil less dense, so more volume!
Common Mistakes
- **Confusing mass and volume flow**: kg/s ≠ L/s unless fluid is water! Need density to convert. Oil, gasoline, air all different!
- **Forgetting density temperature effect**: Hot water less dense than cold. 1 kg/s hot water > 1 L/s. Always specify conditions!
- **US vs UK gallons**: UK gallon 20% larger! 1 gal UK = 1.201 gal US. Check which system!
- **Mixing time units**: GPM ≠ GPH! Check per minute vs per hour vs per second. Factor of 60 or 3600 difference!
- **Standard vs actual conditions (gases)**: Air at different pressures/temperatures has different volume. Specify STP or actual!
- **Assuming incompressible flow**: Gases compress, changes volume! Steam, air, natural gas all affected by pressure/temp.
Fun Facts
Fire Hydrant Power
Typical fire hydrant: 1000-1500 GPM (3800-5700 L/min). That's enough to fill an average bathtub (50 gal) in 3 seconds! Residential water service only 10-20 GPM.
Oil Barrel History
Oil barrel = 42 US gallons. Why 42? In 1860s, whiskey barrels were 42 gallons - oil industry just adopted same size! 1 barrel = 159 liters. World oil measured in million barrels/day.
CFM = Comfort
HVAC rule: 400 CFM per ton of cooling. 3-ton home AC = 1200 CFM. Too low CFM = poor circulation. Too high = energy waste. Just right = comfortable home!
MGD for Cities
Water treatment plants rated in MGD (million gallons per day). New York City: 1000 MGD! That's 3.78 million cubic meters per day. Average person uses 80-100 gallons per day.
Miner's Inch
Historical water rights unit: 1 miner's inch = 0.708 L/s. From gold rush era! Opening 1 square inch in 6-inch head of water. Still used in some western US water rights!
IV Drip Precision
Medical IV drips: 20-100 mL/h. That's 0.33-1.67 mL/min. Critical precision! Drop counting: 60 drops/mL standard. 1 drop per second = 60 mL/h.
History of Flow Measurement
1700s
Early flow measurement. Water wheels, bucket-and-stopwatch method. Venturi effect discovered for flow constriction measurement.
1887
Venturi meter invented. Uses pressure difference in constricted pipe to measure flow. Still used today in modern form!
1920s
Orifice plate meters standardized. Simple, cheap flow measurement. Widely adopted in oil & gas industry.
1940s
Turbine flow meters developed. Rotating blades measure flow velocity. High accuracy, used in aviation fuel.
1970s
Ultrasonic flow meters. No moving parts! Uses sound wave transit time. Non-invasive, accurate for large pipes.
1980s
Mass flow meters (Coriolis). Direct mass measurement, no density needed! Vibrating tube technology. Revolutionary for chemicals.
2000s
Digital flow meters with IoT. Smart sensors, real-time monitoring, predictive maintenance. Integration with building management systems.
Pro Tips
- **Check units carefully**: GPM vs GPH vs GPD. Per minute, hour, or day makes huge difference! Factor of 60 or 1440.
- **Water assumption warning**: Mass to volume converter assumes water (1 kg/L). For oil: multiply by 1.15. For gasoline: multiply by 1.33. For air: multiply by 833!
- **HVAC rule of thumb**: 400 CFM per ton AC. Quick sizing! 3-ton house = 1200 CFM. Convert: 1 CFM = 1.7 m3/h.
- **Pump curves matter**: Flow rate changes with head pressure! Higher head = lower flow. Always check pump curve, don't just use max rating.
- **GPM quick convert**: GPM x 4 ≈ L/min. Close enough for estimates! Exact: x3.785. Reverse: L/min / 4 ≈ GPM.
- **Specify conditions**: Temperature, pressure affect flow (especially gases). Always state standard conditions or actual operating conditions.
- **Scientific notation auto**: Values ≥ 1 million or < 0.000001 automatically display in scientific notation (e.g., 1.0e+6) for readability!
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Metric Volume Flow
| Unit | Symbol | Base Equivalent | Notes |
|---|---|---|---|
| liter per second | L/s | 1 L/s (base) | Commonly used |
| liter per minute | L/min | 16.6667 mL/s | Commonly used |
| liter per hour | L/h | 2.778e-4 L/s | Commonly used |
| liter per day | L/day | 1.157e-5 L/s | — |
| milliliter per second | mL/s | 1.0000 mL/s | Commonly used |
| milliliter per minute | mL/min | 1.667e-5 L/s | Commonly used |
| milliliter per hour | mL/h | 2.778e-7 L/s | — |
| cubic meter per second | m³/s | 1000.0000 L/s | Commonly used |
| cubic meter per minute | m³/min | 16.6667 L/s | Commonly used |
| cubic meter per hour | m³/h | 277.7778 mL/s | Commonly used |
| cubic meter per day | m³/day | 11.5741 mL/s | — |
| cubic centimeter per second | cm³/s | 1.0000 mL/s | — |
| cubic centimeter per minute | cm³/min | 1.667e-5 L/s | — |
US Customary Volume Flow
| Unit | Symbol | Base Equivalent | Notes |
|---|---|---|---|
| gallon (US) per second | gal/s | 3.7854 L/s | Commonly used |
| gallon (US) per minute (GPM) | gal/min | 63.0902 mL/s | Commonly used |
| gallon (US) per hour | gal/h | 1.0515 mL/s | Commonly used |
| gallon (US) per day | gal/day | 4.381e-5 L/s | — |
| cubic foot per second | ft³/s | 28.3168 L/s | Commonly used |
| cubic foot per minute (CFM) | ft³/min | 471.9467 mL/s | Commonly used |
| cubic foot per hour | ft³/h | 7.8658 mL/s | Commonly used |
| cubic inch per second | in³/s | 16.3871 mL/s | — |
| cubic inch per minute | in³/min | 2.731e-4 L/s | — |
| fluid ounce (US) per second | fl oz/s | 29.5735 mL/s | — |
| fluid ounce (US) per minute | fl oz/min | 4.929e-4 L/s | — |
| fluid ounce (US) per hour | fl oz/h | 8.215e-6 L/s | — |
Imperial Volume Flow
| Unit | Symbol | Base Equivalent | Notes |
|---|---|---|---|
| gallon (Imperial) per second | gal UK/s | 4.5461 L/s | Commonly used |
| gallon (Imperial) per minute | gal UK/min | 75.7682 mL/s | Commonly used |
| gallon (Imperial) per hour | gal UK/h | 1.2628 mL/s | Commonly used |
| gallon (Imperial) per day | gal UK/day | 5.262e-5 L/s | — |
| fluid ounce (Imperial) per second | fl oz UK/s | 28.4131 mL/s | — |
| fluid ounce (Imperial) per minute | fl oz UK/min | 4.736e-4 L/s | — |
| fluid ounce (Imperial) per hour | fl oz UK/h | 7.893e-6 L/s | — |
Mass Flow Rate
| Unit | Symbol | Base Equivalent | Notes |
|---|---|---|---|
| kilogram per second | kg/s | 1 L/s (base) | Commonly used |
| kilogram per minute | kg/min | 16.6667 mL/s | Commonly used |
| kilogram per hour | kg/h | 2.778e-4 L/s | Commonly used |
| gram per second | g/s | 1.0000 mL/s | — |
| gram per minute | g/min | 1.667e-5 L/s | — |
| gram per hour | g/h | 2.778e-7 L/s | — |
| metric ton per hour | t/h | 277.7778 mL/s | — |
| metric ton per day | t/day | 11.5741 mL/s | — |
| pound per second | lb/s | 453.5920 mL/s | — |
| pound per minute | lb/min | 7.5599 mL/s | — |
| pound per hour | lb/h | 1.260e-4 L/s | — |
Specialized & Industry
| Unit | Symbol | Base Equivalent | Notes |
|---|---|---|---|
| barrel per day (oil) | bbl/day | 1.8401 mL/s | Commonly used |
| barrel per hour (oil) | bbl/h | 44.1631 mL/s | — |
| barrel per minute (oil) | bbl/min | 2.6498 L/s | — |
| acre-foot per day | acre-ft/day | 14.2764 L/s | Commonly used |
| acre-foot per hour | acre-ft/h | 342.6338 L/s | — |
| million gallons per day (MGD) | MGD | 43.8126 L/s | Commonly used |
| cusec (cubic foot per second) | cusec | 28.3168 L/s | Commonly used |
| miner's inch | miner's in | 708.0000 mL/s | — |
FAQ
What's the difference between GPM and CFM?
GPM = gallons (liquid) per minute. Used for water, liquids. CFM = cubic feet (air/gas) per minute. Used for HVAC airflow. Different fluids! 1 GPM water weighs 8.34 lb/min. 1 CFM air weighs 0.075 lb/min at sea level. Volume same, mass very different!
Can I convert kg/s to L/s?
YES, but need fluid density! Water: 1 kg/s = 1 L/s (density 1 kg/L). Oil: 1 kg/s = 1.15 L/s (density 0.87 kg/L). Gasoline: 1 kg/s = 1.33 L/s (density 0.75 kg/L). Air: 1 kg/s = 833 L/s (density 0.0012 kg/L)! Always check density. Our converter assumes water if not specified.
Why does my pump flow rate change?
Pump flow varies with head pressure! Higher lift/pressure = lower flow. Pump curve shows flow vs head relationship. At zero head (open discharge): max flow. At max head (closed valve): zero flow. Check pump curve for actual operating point. Never use just max flow rating!
How much flow for my HVAC system?
Rule of thumb: 400 CFM per ton of cooling. 3-ton AC = 1200 CFM. 5-ton = 2000 CFM. In metric: 1 ton ≈ 680 m3/h. Adjust for ductwork resistance. Too low = poor cooling. Too high = noise, energy waste. Professional load calculation recommended!
What's the difference between US and UK gallons?
BIG difference! Imperial (UK) gallon = 4.546 liters. US gallon = 3.785 liters. UK gallon 20% LARGER! 1 gal UK = 1.201 gal US. Always specify which system! Most converters default to US gallons unless stated 'Imperial' or 'UK'.
How do I size a pump?
Three steps: 1) Calculate required flow (volume/time needed). 2) Calculate total head (lift height + friction losses). 3) Select pump where operating point (flow + head) is 80-90% of best efficiency point (BEP) on pump curve. Add 10-20% safety margin. Check NPSH requirements. Consider system curve!
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