* Millimeters (mm) measure length or distance.
* Liters (L) measure volume.
* Gallons (gal) measure volume.
To convert between volume units, you need to know the density of the substance you're measuring.
For example:
* If you're talking about 5 millimeters of water per liter of water, you can convert to gallons.
* You can't convert 5 millimeters of air per liter of air to gallons, because the density of air is much lower than water.
To make the conversion, you'd need to know:
1. What substance you are measuring.
2. The density of that substance in grams per milliliter (g/mL).
Let me know if you can provide those details, and I can help you with the conversion.
