Flow Rate Converter
Convert flow rate between units instantly. Includes conversion tables, common equivalents, and calculation formulas. Includes formulas and worked examples.
Flow Rate Converter
Calculator
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Formula: Converted Flow = Input x (From Factor / To Factor); Velocity = Flow Rate / Pipe Area
Worked example — 10 GPM = 37.8541 L/min
Formula
Converted Flow = Input x (From Factor / To Factor); Velocity = Flow Rate / Pipe Area
Each flow rate unit has a conversion factor to liters per minute (LPM) as the base unit. The input value is multiplied by the source factor and divided by the target factor. Fluid velocity through a pipe equals the volumetric flow rate divided by the pipe cross-sectional area (pi times radius squared).
Worked Examples
Example 1: Converting GPM to Liters per Minute
Problem:Convert 10 US gallons per minute to liters per minute.
Solution:L/min = GPM x 3.78541 L/min = 10 x 3.78541 = 37.8541 L/min
Result:10 GPM = 37.8541 L/min
Example 2: Flow Velocity in a Pipe
Problem:Find velocity for 20 L/min through a 1-inch (25.4mm) pipe.
Solution:Area = pi x (0.0127)^2 = 0.0005067 m2 Flow = 20 / 60000 = 0.000333 m3/s Velocity = 0.000333 / 0.0005067 = 0.658 m/s
Result:Velocity: 0.658 m/s (2.158 ft/s)
Frequently Asked Questions
What is flow rate and how is it measured?
Flow rate is the volume of fluid passing through a point per unit time. It is commonly measured in liters per minute, gallons per minute, or cubic meters per hour depending on the application. Volumetric flow rate is calculated by multiplying the cross-sectional area of the pipe or channel by the average fluid velocity. Industrial flow meters use various principles including differential pressure, electromagnetic induction, ultrasonic transit time, and Coriolis force to measure flow rates accurately.
How do I calculate fluid velocity from flow rate and pipe diameter?
Fluid velocity equals the volumetric flow rate divided by the cross-sectional area of the pipe. The pipe area equals pi times the radius squared. For example, with a flow rate of 10 liters per minute through a 25mm diameter pipe: area = pi times 0.0125 squared = 0.000491 square meters. Converting 10 L/min to 0.000167 cubic meters per second, velocity = 0.000167 divided by 0.000491 = 0.340 meters per second. Higher velocity generally means more turbulence and pressure drop.
What is the difference between volumetric and mass flow rate?
Volumetric flow rate measures the volume of fluid passing per unit time (liters/min, gallons/min), while mass flow rate measures the mass passing per unit time (kg/s, lb/hr). They are related by fluid density: mass flow rate equals volumetric flow rate times density. For water at standard conditions, 1 liter per minute equals approximately 1 kilogram per minute. The distinction matters for gases, whose density changes significantly with temperature and pressure, making mass flow rate more reliable for gas metering.
What are typical flow rates for household plumbing?
Standard household fixtures have regulated flow rates to conserve water. Kitchen faucets typically deliver 6-8 liters per minute (1.5-2 GPM). Showerheads are limited to about 9.5 L/min (2.5 GPM) in the US. Toilets use 6 liters (1.6 gallons) per flush. A garden hose delivers 30-60 L/min (8-15 GPM). The main supply line to a house typically handles 40-75 L/min (10-20 GPM), and exceeding this can cause pressure drops throughout the home.
What is the difference between a US gallon per minute and an Imperial gallon per minute?
The two gallons are different volumes. A US liquid gallon is 3.78541 litres, while an Imperial (UK) gallon is 4.54609 litres, about 20 percent larger. So 10 US GPM is 37.85 L/min but 10 Imperial GPM is 45.46 L/min. This converter uses the US gallon. Pump curves and fixture ratings sourced from UK or Commonwealth suppliers may be in Imperial gallons, so confirm the gallon definition before comparing equipment across markets.
How is the barrels-per-day unit defined in oil and gas work?
One oil barrel is 42 US gallons, or 158.987 litres, and BPD spreads that over 1,440 minutes in a day. That makes 1 BPD equal to 158.987 / 1440 = 0.11041 L/min, a very small instantaneous rate. Because production is quoted as a daily average, BPD smooths out downtime and pump cycling, which is why a well rated at 1,000 BPD does not flow at a steady 110 L/min through every minute of the day.
How do you tell whether the flow in your pipe is laminar or turbulent?
Compute the Reynolds number, Re = velocity x diameter / kinematic viscosity. For water near 20 degrees Celsius the kinematic viscosity is about 1.0 x 10^-6 m2/s. Taking the 0.34 m/s velocity in a 25 mm pipe from the velocity example gives Re of roughly 8,500. Flow is generally laminar below about 2,300 and fully turbulent above about 4,000, so that pipe is turbulent, which raises friction loss but improves mixing and heat transfer.
What is the difference between ACFM and SCFM for air flow?
Actual cubic feet per minute measures the real volume passing at the local temperature and pressure, while standard cubic feet per minute normalises that volume to an agreed reference condition. Because gases are compressible, the same mass of air occupies far less volume at high pressure, so a compressor outlet reading in ACFM will be much lower than the SCFM it delivers. Always check which basis a rating uses before converting compressed-air flows with a volumetric factor.
Why does pipe velocity matter as much as the flow rate itself?
Friction loss in the Darcy-Weisbach equation scales with the square of velocity, so doubling velocity in the same pipe roughly quadruples the pressure drop the pump must overcome. High velocities also cause noise, water hammer on valve closure, and erosion of pipe walls and elbows. Very low velocities let sediment settle out. Using the velocity output alongside the converted flow lets you check that a chosen pipe diameter sits in a sensible band.
How do you turn a flow rate into a tank fill time?
Divide the tank volume by the flow rate in matching units. A 1,000 litre tank fed at 10 GPM, which this tool converts to 37.85 L/min, fills in 1,000 / 37.85 = 26.4 minutes. Convert both quantities to the same volume unit first, since mixing gallons with litres is the usual source of error. Add margin for the supply pressure dropping as the tank head rises, because most pumps deliver less flow against higher discharge pressure.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator · Editorial policy
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