Gallons to Fluid Ounces Converter

How to convert U.S. gallons to U.S. fluid ounces

To convert U.S. gallons to U.S. fluid ounces, multiply the number of U.S. gallons by 128.

Example: 1 gal = 128 fl oz.

A U.S. gallon is 128 fluid ounces — a common daily water goal.

Common gal to fl oz conversions

• 0.5 gal = 64 fl oz
• 1 gal = 128 fl oz
• 2 gal = 256 fl oz
• 5 gal = 640 fl oz
• 10 gal = 1,280 fl oz
• 15 gal = 1,920 fl oz
• 20 gal = 2,560 fl oz
• 50 gal = 6,400 fl oz
• 55 gal = 7,040 fl oz
• 100 gal = 12,800 fl oz

Gallons to Fluid Ounces conversion chart

Metric vs. U.S. customary units

The United States uses U.S. customary units — inches, feet, miles, pounds, gallons and degrees Fahrenheit — for most everyday purposes. Canada officially adopted the metric system in the 1970s, so road signs, weather forecasts, gas pumps and food labels use kilometers, degrees Celsius, liters and grams. In practice many Canadians still use feet and inches for height, pounds for body weight and square feet for homes, which is why conversions come up constantly on both sides of the border.

Exact conversion factors

Since 1959 the inch, foot, yard, mile and pound have been defined in metric terms, so these conversions are exact, not approximations:

• 1 inch = 2.54 cm exactly, so 1 foot = 30.48 cm and 1 mile = 1.609344 km.
• 1 pound = 0.45359237 kg exactly; 1 ounce = 28.349523125 g.
• 1 U.S. gallon = 3.785411784 liters. The imperial gallon used in the U.K. is larger: 4.54609 liters.
• 1 acre = 4,046.8564224 m², and 1 hectare = 10,000 m² (about 2.471 acres).

Temperature is different because the scales have different zero points: °F = °C × 9/5 + 32 and °C = (°F − 32) × 5/9. Water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F) at sea level, and −40 is the same in both scales.

Quick mental shortcuts

• Kilometers to miles: multiply by 0.6 (100 km ≈ 60 miles; the exact figure is 62.1).
• Kilograms to pounds: double it and add 10% (70 kg → 140 + 14 = 154 lb).
• Celsius to Fahrenheit: double it and add 30 for a rough estimate (20 °C → 70 °F; the exact answer is 68 °F).
• Liters to U.S. gallons: divide by 4 for a quick estimate (40 L ≈ 10 gallons; exactly 10.57).

Cooking and recipe conversions

U.S. recipes measure by volume — cups, tablespoons and teaspoons — while Canadian and most international recipes use milliliters and grams. A U.S. cup is about 237 mL, but Canadian "metric" measuring cups hold 250 mL, so the difference adds up in baking. For flour, sugar and butter, weighing in grams is more accurate than cups because the density of each ingredient differs.

Popular conversions

Pick a conversion below for a dedicated page with the formula, worked examples and a complete conversion chart.

Tips for accurate conversions

Keep full precision until the final step and round only the answer — rounding intermediate numbers can add noticeable errors, especially in recipes, construction and engineering. Always check which gallon, ounce or ton a source means: U.S. and imperial units share names but not sizes, and a "fluid ounce" measures volume while an "ounce" of weight measures mass. For temperatures, remember that a temperature difference converts differently from a temperature reading: a change of 10 °C equals a change of 18 °F, without adding 32.

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Frequently asked questions

Sources & methodology

This calculator was last reviewed on November 2, 2026. Figures are based on the following official and primary sources:

• NIST – Handbook 44, Appendix C: General Tables of Units of Measurement

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