Why Convert Gallons per Hour to Litres per Hour?

Whether you’re sizing a water pump, calibrating an HVAC system, or comparing fuel‑flow specs, you’ll often need to translate gallons per hour (gal/h) into litres per hour (l/h). Using the wrong unit can lead to undersized equipment, wasted energy, or costly re‑work.

Understanding the Measure: Volume Flow Rate

Volume flow rate measures how much fluid passes a point in a given time. It belongs to the broader “Volume” family, but adds the time dimension. In the International System of Units (SI), the standard unit is cubic metres per second (m³/s). In everyday practice, especially in the United States, gallons per hour is common, while most of the world uses litres per hour.

Gallon per Hour (gal/h)

A gallon per hour tells you how many US liquid gallons flow each hour. One US gallon equals exactly 3.785411784 litres.

Litre per Hour (l/h)

A litre per hour indicates the volume in litres that moves each hour. It is the SI‑compatible counterpart to gal/h.

Exact Conversion Factor

The relationship is fixed:

1 gal/h = 3.785411784 l/h

Because the factor is precise, you can rely on it for engineering calculations, budgeting, or simple DIY projects.

Conversion Formula

To turn any flow rate from gallons per hour into litres per hour, multiply by the factor:

Litres per hour = Gallons per hour × 3.785411784

Conversely, to go from litres per hour to gallons per hour, divide by the same number.

Worked Example: Sizing a Garden Irrigation Pump

Imagine a pump rated at 12 gal/h. You need the flow in litres per hour to match a European‑spec irrigation controller.

1. Identify the source value: 12 gal/h.
2. Apply the formula: 12 × 3.785411784 = 45.424941408 l/h.
3. Round to a practical precision (four decimal places): 45.4249 l/h.

The pump delivers roughly 45.425 l/h, which you can now compare directly with the controller’s 40 l/h requirement.

Practical Applications of the gal/h ↔ l/h Conversion

• Water treatment plants: Equipment specs often mix US and metric units.
• Automotive cooling systems: Radiator flow rates are quoted in gal/h in the US, but many parts catalogs use l/h.
• HVAC design: Air‑handling units may list coolant flow in gal/h, while building codes require l/h.
• Industrial process control: Sensors output in gal/h; control software expects l/h.
• DIY projects: Homebrew fermenters, aquarium filters, and garden pumps benefit from a quick conversion.

Tips for Accurate Flow‑Rate Conversion

1. Use the full factor (3.785411784) in calculations, then round only for reporting.
2. Check the gallon type: The factor above applies to the US liquid gallon. The UK (imperial) gallon equals 4.54609 l, which is a different conversion.
3. Maintain consistent units throughout a project to avoid hidden errors.
4. Document the conversion in project notes so teammates can verify the numbers.

Gallon Per Hour to Litre Per Hour Conversion Table

Each row applies the same rule: multiply gallons per hour by 3.785411784 and round to four decimal places.

Key Takeaway

One US gallon per hour always equals 3.785411784 litres per hour. Keep this factor handy, apply the simple multiplication formula, and you’ll convert fluid flow rates confidently across any project.

Ready to streamline your calculations? Bookmark this guide and use the table whenever you need a quick, reliable conversion.