Which conversion factor correctly converts gallons to milliliters?

• A. 3,785 milliliters per gallon
• B. 1,000 milliliters per gallon
• C. 500 milliliters per gallon
• D. 128 milliliters per gallon

Answer: (A)

Converting gallons to milliliters uses the relationship between liters and milliliters and between gallons and liters. A US gallon equals about 3.785 liters, and 1 liter equals 1,000 milliliters. Multiply to get 3.785 × 1,000 = 3,785 milliliters per gallon. That’s why the correct answer is 3,785 milliliters per gallon. The other numbers would imply much smaller amounts per gallon—for example, 1,000 mL per gallon would mean only 1 liter per gallon, which isn’t correct; 500 mL per gallon and 128 mL per gallon are even smaller still.