Gallons to Fluid Ounces
Convert gallons (gal) to fluid ounces (fl oz). Both measure capacity and volume, and the conversion comes up in cooking, chemistry, fuel work.
The Formula
``
fluid ounces = gallons × 128
gallons = fluid ounces × 0.0078125
`
One gallon is 128 fluid ounces, and one fluid ounce is 0.007813 gallons.
Conversion Table
| Gallons | Fluid Ounces |
|---|---|
| 1 gal | 128 fl oz |
| 2 gal | 256 fl oz |
| 5 gal | 640 fl oz |
| 10 gal | 1,280 fl oz |
| 25 gal | 3,200 fl oz |
| 50 gal | 6,400 fl oz |
| 100 gal | 12,800 fl oz |
| 500 gal | 64,000 fl oz |
| 1,000 gal | 128,000 fl oz |
The Other Direction
| Fluid Ounces | Gallons |
|---|---|
| 1 fl oz | 0.007813 gal |
| 2 fl oz | 0.015625 gal |
| 5 fl oz | 0.039063 gal |
| 10 fl oz | 0.078125 gal |
| 25 fl oz | 0.195313 gal |
| 50 fl oz | 0.390625 gal |
| 100 fl oz | 0.78125 gal |
| 500 fl oz | 3.9063 gal |
| 1,000 fl oz | 7.8125 gal |
What Each Unit Is
Gallons (gal) — the US liquid gallon: exactly 3.785411784 litres. The English wine gallon of 231 cubic inches, kept by the US after Britain moved on in 1824.
Fluid Ounces (fl oz) — the US fluid ounce: exactly 29.5735295625 millilitres. One sixteenth of a US pint, descended from the wine gallon.
A Sense of Scale
A US milk jug is 1 gallon- A car tank is 12–16 gallons
- US fuel economy is miles per gallon
- A shot is 1.5 fl oz
- A soda can is 12 fl oz
- A US coffee cup is 8 fl oz
Precision
The factor 128 is rounded. For engineering work carry more digits than the table above, and round only at the end — rounding at each step compounds.
Watch Out For
- The UK imperial gallon is 4.546 litres — 20% larger. A "gallon" without a country attached is ambiguous, and US MPG figures look worse when read as imperial.
- A UK fluid ounce is 28.41 mL — close enough to confuse, far enough to ruin a cocktail.
In Code
`javascript
const gallonToFluidOunce = (value) => value * 128;
``
Where This Conversion Comes Up
- Cooking
- Chemistry
- Fuel
- Beverages
- Medicine
How Many Decimals Do You Need?
Rounding the factor costs accuracy, and how much depends on the factor. Converting 137 gal with the factor truncated at each decimal place:
| Decimals kept | Factor | 137 gal becomes | Error |
|---|---|---|---|
| 0 | 128 | 17,536 | — |
| 1 | 128 | 17,536 | — |
| 2 | 128 | 17,536 | — |
| 3 | 128 | 17,536 | — |
| 4 | 128 | 17,536 | — |
The right number of significant figures is set by your input, not by the converter. If you measured gallons to three significant figures, the answer in fluid ounces is only good to three — writing more digits claims precision the measurement never had.