Gallons, Liters, and Cups: A Practical Volume Conversion Guide

Volume conversion comes up constantly in cooking, shopping, science, and international trade. The challenge is that different countries not only use different units but sometimes use the same name for different sizes.

Metric Volume Units

The metric system keeps volume simple:

• 1 liter (L) = 1,000 milliliters (mL)
• 1 milliliter = 1 cubic centimeter (cm³)
• 1 cubic meter = 1,000 liters

US Customary Volume Units

The US system is more complex:

• 1 US gallon = 4 quarts = 8 pints = 16 cups = 128 fluid ounces = 3.785 liters
• 1 quart = 2 pints = 4 cups = 32 fl oz = 946.4 mL
• 1 pint = 2 cups = 16 fl oz = 473.2 mL
• 1 cup = 8 fl oz = 236.6 mL
• 1 fluid ounce = 2 tablespoons = 29.6 mL

US vs Imperial Gallons

This is a common source of confusion. The US and Imperial (UK) gallons are different:

• US gallon = 3.785 liters
• Imperial gallon = 4.546 liters

An Imperial gallon is about 20% larger than a US gallon. This affects all related units (pints, quarts, etc.) as well.

Practical Volume References

• A can of soda: 355 mL (12 fl oz)
• A wine bottle: 750 mL
• A water bottle: 500 mL or 1 L
• A bathtub: ~150-300 liters (40-80 US gallons)
• A swimming pool: ~50,000-80,000 liters

Quick Mental Conversions

• 1 liter ≈ 1 US quart (close enough for estimates)
• 4 liters ≈ 1 US gallon
• 1 cup ≈ 240 mL (round from 236.6 for easy math)
• 1 tablespoon ≈ 15 mL