From L H to GPM: A Practical Guide to Flow Unit Conversion
In many industries—HVAC, plumbing, industrial processing, and even home DIY projects—flow rates are expressed in a variety of units. A common scenario is the need to convert liters per hour (L/H) into gallons per minute (GPM). This conversion is essential when comparing equipment specifications, reading pump curves, or sizing filters that are rated in gallons per hour. The following article walks through the science behind the conversion, step‑by‑step methods, and how to avoid common pitfalls.
Why Convert L/H to GPM?
Different regions and industries prefer different units:
- Liters per hour (L/H) is common in Europe and for scientific measurements.
- Gallons per minute (GPM) is widely used in the United States, especially for pump and filter specifications.
When you encounter a pump curve that lists flow in gallons per hour (GPH) and you need GPM, or when a filter rating is given in L/H, you must perform a conversion to make meaningful comparisons.
The Conversion Factor
Both liters and gallons are units of volume, while hours and minutes are units of time. The conversion hinges on two relationships:
- 1 gallon (US) = 3.78541 liters
- 1 hour = 60 minutes
To convert from L/H to GPM, you combine these two ratios:
GPM = (L/H ÷ 3.78541) ÷ 60
Or, more simply:
GPM = L/H × 0.00422675
Conversely, to go from GPM to L/H, multiply by 3.78541 and then by 60:
L/H = GPM × 3.78541 × 60 = GPM × 227.1426
Step‑by‑Step Conversion Example
Suppose a filter is rated at 1200 L/H. To express this in GPM:
- Divide 1200 by 3.78541: 1200 ÷ 3.78541 ≈ 317.3 gallons per hour.
- Divide by 60 to convert hours to minutes: 317.3 ÷ 60 ≈ 5.29 GPM.
- Result: The filter handles about 5.3 GPM.
Alternatively, using the single‑step factor:
1200 × 0.00422675 ≈ 5.07 GPM. The slight difference is due to rounding.
Using Online Conversion Tools
Manual calculations are straightforward, but they can be tedious when dealing with large datasets or multiple conversions. Two reliable online resources
