This converter turns US gallons into US fluid ounces instantly, using the exact factor 1 US gallon = 128 US fluid ounces. Type any number and the result updates as you go — nothing is sent to a server, so the arithmetic happens entirely in your browser.
Exactly 231 cubic inches — the US liquid gallon used for fuel and milk. One eighth of a US cup, roughly 29.57 millilitres.
Because the relationship is a simple proportion, one multiplication does the whole job. The table further down gives pre-computed values for the amounts people look up most often, and the result panel also reports the reverse conversion so you can check the figure both ways.
The formula
US gallons- The amount you are converting, measured in US gallons
128- The exact number of US fluid ounces in one US gallon
US fluid ounces- The converted result
How it works, step by step
- Enter the number of US gallons you want to convert.
- The value is multiplied by 128, the exact conversion factor.
- The result is displayed in US fluid ounces, rounded for readability.
- The unrounded value and the reverse conversion appear underneath so you can verify it.
Worked examples
Converting 5 US gallons
Multiply 5 by 128. That gives 640 US fluid ounces. A quick sanity check: one US gallon is larger than one US fluid ounce, so the number should get bigger — and it does.
Converting 72 US gallons
72 × 128 = 9,216 US fluid ounces. Working backwards, 9,216 ÷ 128 returns 72 US gallons, which confirms the factor is applied the right way round.
How to read your score
Frequently asked questions
How many US fluid ounces are in one US gallon?
Exactly 128. Every conversion on this page is that single number multiplied by your input, so the result carries no rounding error beyond what is shown.
What is the formula to convert US gallons to US fluid ounces?
Us Fluid Ounces = US gallons × 128. To reverse it, divide instead: US gallons = US fluid ounces ÷ 128, which is the same as multiplying by 0.0078125.
Is the US gallon bigger than the US fluid ounce?
Yes. One US gallon equals 128 US fluid ounces, so it is the larger unit.
Why does my answer differ slightly from other us-gallons to us-fluid-ounces converters?
Most differences come from rounding the factor too early. This tool keeps full double precision through the calculation and only rounds at the final display step, and it also shows the unrounded value so you can see exactly where any difference appears.
What is a US gallon?
Exactly 231 cubic inches — the US liquid gallon used for fuel and milk.
What is a US fluid ounce?
One eighth of a US cup, roughly 29.57 millilitres.
Us Gallons to US fluid ounces reference table
| Us Gallons | Us Fluid Ounces |
|---|---|
| 0.5 gal | 64 fl oz |
| 1 gal | 128 fl oz |
| 2 gal | 256 fl oz |
| 3 gal | 384 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 |
| 25 gal | 3,200 fl oz |
| 50 gal | 6,400 fl oz |
| 75 gal | 9,600 fl oz |
| 100 gal | 12,800 fl oz |
| 250 gal | 32,000 fl oz |
| 500 gal | 64,000 fl oz |
| 1000 gal | 128,000 fl oz |
Exact factor: 1 US gallon = 128 US fluid ounces. Values rounded for display.