Convert US Gallon to US Fluid Ounce
Convert us gallons to us fluid ounces instantly. 1 us gallon = 128 us fluid ounce — use the live calculator, the exact formula, a conversion table and worked examples. Also check the US Fluid Ounce to US Gallon converter for the reverse conversion.
Units explained
US Gallon
The US liquid gallon is defined as exactly 231 cubic inches (3.785411784 liters).
Based on the English wine gallon of 231 cubic inches, retained by the US after 1824.
The primary US unit for fuel, milk and large beverage containers.
English wine gallon; US since 1824.
US Fluid Ounce
A US fluid ounce is 1/128 of a US gallon (29.5735 mL).
Derived from the gallon subdivision; distinct from the slightly smaller UK fluid ounce.
Standard for US beverage and nutrition labeling.
English customary; US since 1824.
US Gallon to US Fluid Ounce conversion formula
The relationship between us gallons and us fluid ounces:
To convert us gallons to us fluid ounces, multiply the value in us gallons by 128. To reverse, multiply us fluid ounces by 0.0078125.
How to use this converter
Type a value into the calculator. The result in us fluid ounces updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the US Fluid Ounce to US Gallon converter for the reverse direction.
Step-by-step: convert us gallons to us fluid ounces
- Write down the value in us gallons (gal).
- Multiply that value by the factor 128.
- The product is the equivalent value in us fluid ounces (fl oz).
- To reverse, multiply the us fluid ounce value by 0.0078125.
Worked examples
Example 1 — Convert 1 gal to fl oz:
1 × 128 = 128 fl oz
Example 2 — Convert 100 gal to fl oz:
100 × 128 = 12800 fl oz
Real-world example — Adjacent metric sub-units
One us gallon equals 1,000 us fluid ounces. Engineers move between these scales constantly: PCB feature sizes in the larger unit, wire-bond diameters in the smaller.
1 gal × 128 = 128 fl oz
Real-world example — Adjacent small-scale precision
One us gallon equals 1,000 us fluid ounces — the standard sub-millimeter precision conversion that materials engineers use whenever they switch between bulk material thickness specs (larger unit) and surface-finish characteristics (smaller unit).
1 gal × 128 = 128 fl oz
US Gallon to US Fluid Ounce conversion table
Standard reference values for converting us gallons to us fluid ounces:
| US Gallon [gal] | US Fluid Ounce [fl oz] |
|---|---|
| 0.01 | 1.28 |
| 0.1 | 12.8 |
| 1 | 128 |
| 2 | 256 |
| 3 | 384 |
| 4 | 512 |
| 5 | 640 |
| 10 | 1280 |
| 20 | 2560 |
| 30 | 3840 |
| 40 | 5120 |
| 50 | 6400 |
| 100 | 12800 |
| 500 | 64000 |
| 1000 | 128000 |
Frequently asked questions
How many us fluid ounces is 1 us gallon?
How do I convert us gallons to us fluid ounces?
How do I convert us fluid ounces back to us gallons?
How many us fluid ounces is 100 us gallons?
Popular volume unit conversions
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Metric / SI (15 units)
US Customary (Liquid) (14 units)
US Customary (Dry) (5 units)
Imperial (UK) (14 units)
Cubic (length-derived) (4 units)
Cooking / Culinary (5 units)
Sources & references
Conversion factor (1 gal = 128 fl oz) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
- International Hydrographic Organization — Resolution on the Nautical Mile
International authority that standardised the nautical mile at exactly 1852 m in 1929 — the value adopted worldwide for sea and air navigation.