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Flow Converter

Science

Convert flow rate units including litres per minute, cubic metres per hour, GPM, and CFM. Ideal for plumbing, irrigation, and industrial engineering projects.

Reviewed by the thecalcu.com team · Last updated July 15, 2026

From
To
All conversionsfor 1 Litre per Minute (L/min)
Cubic Metre per Second (m³/s)0.0000166667
Cubic Metre per Minute (m³/min)0.001
Cubic Metre per Hour (m³/h)0.060000072
Litre per Second (L/s)0.0166667
Litre per Minute (L/min)1
Litre per Hour (L/h)60.000072
Millilitre per Second (mL/s)16.6667
Millilitre per Minute (mL/min)1000
US Gallon per Minute (GPM)0.26417257
US Gallon per Hour (GPH)15.850404
Cubic Foot per Minute (CFM)0.035314771
Cubic Foot per Second (CFS)0.00058857992
UK Gallon per Minute (GPM)0.21996959
UK Gallon per Hour (GPH)13.19821

What is a Flow?

The Flow Converter converts volumetric flow rate between SI units (m³/s, m³/min, m³/h), metric units (L/s, L/min, L/h, mL/s, mL/min), and US Customary and Imperial units (GPM, GPH, CFM, CFS, both US and UK gallon variants). Every unit routes through a shared base unit, cubic metres per second, so any pair of units can be converted directly against each other with a single lookup. This kind of conversion comes up constantly in plumbing, irrigation design, HVAC sizing, and industrial process engineering, where equipment specs, local codes, and international standards rarely agree on a single unit. Whether you're comparing a US-made pump's GPM rating against a European spec in L/min, or converting CFM airflow figures for an HVAC job, this tool handles the arithmetic instantly and precisely.

How to use this Flow calculator

  1. Select your source unit from the "from" dropdown, for example, "Litre per Minute (L/min)".
  2. Select your target unit from the "to" dropdown, for example, "Cubic Metre per Hour (m³/h)".
  3. Enter the flow rate value you want to convert in the input field.
  4. Read the converted result instantly as you type, no need to click a separate "convert" button.
  5. Switch units using the swap control if you need to reverse the conversion direction.
  6. Double-check whether you need the US or UK version of gallon-based units (GPM, GPH), since they represent different volumes.

Why Use a Flow Converter?

Flow rate units multiply fast once you're working across disciplines or countries, a US-sourced pump spec sheet in GPM, a European HVAC standard in m³/h, and an irrigation system rated in L/min can all show up on the same project. Converting these by hand means chaining multiple conversion factors and hoping you didn't drop a decimal somewhere, which matters when a pump undersized by even 10% can fail to meet a system's demand. This tool is built for exactly that friction point: comparing equipment specs across regions, verifying a manufacturer's claimed flow rate against a project requirement, or translating a client's preferred unit into whatever your own calculations use.

Formula & Methodology

Each unit has a fixed toBase factor that converts it to the shared base unit, cubic metres per second (m³/s). Converting between any two units A and B follows:

value_B = value_A × toBase(A) / toBase(B)

Where:
- value_A = your input flow rate in unit A
- toBase(A) = the conversion factor from unit A to m³/s
- toBase(B) = the conversion factor from unit B to m³/s

Worked example: Converting 100 L/min to m³/h:

toBase(L/min) = 0.0000166667, toBase(m³/h) = 0.000277778

value_(m³/h) = 100 × 0.0000166667 / 0.000277778 = 0.00166667 / 0.000277778 = 6 m³/h

So 100 litres per minute equals exactly 6 cubic metres per hour, a clean number that's easy to sanity-check, since 100 L/min × 60 min/h = 6,000 L/h = 6 m³/h.

Common Mistakes to Avoid

  • Confusing US and UK gallons. GPM (US) and GPM (UK) differ by about 20%, always confirm which gallon standard your source spec uses before converting.
  • Mixing up per-second and per-minute units. CFM and CFS look similar but differ by a factor of 60, misreading one for the other is a common and costly sizing error.
  • Assuming CFM always means "standard" conditions. In HVAC and gas engineering, CFM readings can be at actual or standard temperature/pressure, this converter does a pure unit conversion and doesn't adjust for that distinction.
  • Rounding intermediate results. For multi-step conversions, let the converter handle the full-precision math rather than rounding L/min to a whole number before converting to m³/h.

Quick Reference

From To Multiply by
L/min m³/h 0.06
GPM (US) L/min 3.785
CFM L/s 0.4719
m³/h GPM (US) 4.403

For related unit work, see the Volume Converter for static volume conversions, the Pressure Converter if you're sizing a system that involves both flow and pressure specs, or the Speed Converter when a flow problem also involves velocity through a pipe or duct.

Frequently Asked Questions

All conversions route through cubic metres per second (m³/s), the SI base unit for volumetric flow rate. Every other unit, L/min, GPM, CFM, and the rest, has a fixed toBase factor that converts to and from m³/s, which keeps the math consistent regardless of which two units you're converting between.
A US gallon (3.785 litres) is smaller than a UK imperial gallon (4.546 litres), so GPM (US) and GPM (UK) represent different actual flow rates even though the unit name looks the same. This converter lists them separately precisely because mixing them up is a common and costly error in cross-border engineering specs.
Different industries and equipment specs default to different units, plumbing often uses L/min, industrial process engineering favors m³/h, and HVAC frequently uses CFM. Converting lets you compare a pump's rated output against a spec sheet or standard that uses a different unit without redoing the math by hand.
The conversion factors used here are standard, published constants (like 0.0000630902 m³/s per US GPM), accurate to at least 6 significant figures. For final engineering documentation, always cross-check against your governing standard's official conversion table, but for sizing estimates and quick checks this level of precision is more than sufficient.
Select CFM as your 'from' unit and L/s as your 'to' unit, then enter your flow rate, the converter handles the two-step conversion (CFM to m³/s, then m³/s to L/s) internally so you get a direct answer without manual intermediate steps.
US Customary and British Imperial units share some names (gallon, ounce) but differ in actual size, so this converter separates them into distinct groups to avoid the ambiguity. GPM (US) and GPM (UK) are a good example, same abbreviation, meaningfully different volumes.
Yes, volumetric flow rate conversion works identically whether the fluid is a liquid or a gas, since the units describe volume per time regardless of what's flowing. Just be aware that for gases, flow rate readings are often specified at a reference temperature and pressure (like standard CFM vs actual CFM), which this converter doesn't adjust for.
A standard shower head flows around 6-8 L/min (roughly 1.6-2.1 US GPM) under typical US building codes, while a whole-house water supply line might handle 40-60 L/min at peak demand. These numbers vary by fixture type and local plumbing codes, so treat them as rough reference points.
No, this converter handles volumetric flow rate only (volume per time). Mass flow rate depends on the fluid's density, which varies by substance and temperature, so it needs a separate calculation that factors in density rather than a fixed unit conversion.
The unit chosen tends to match the typical magnitude of flow in that field, river discharge and large industrial pumping involve much larger volumes per unit time, so CFS avoids unwieldy large numbers, while HVAC airflow is naturally smaller and fits comfortably in CFM.
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