This converter turns US gallons into imperial fluid ounces instantly, using the exact factor 1 US gallon = 133.2278695 imperial 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. The UK fluid ounce, about 4% smaller than its US counterpart.
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
133.2278695- The exact number of imperial fluid ounces in one US gallon
imperial 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 133.2278695, the exact conversion factor.
- The result is displayed in imperial 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 133.22787. That gives 666.1393 imperial fluid ounces. A quick sanity check: one US gallon is larger than one imperial fluid ounce, so the number should get bigger — and it does.
Converting 72 US gallons
72 × 133.22787 = 9,592.41 imperial fluid ounces. Working backwards, 9,592.41 ÷ 133.22787 returns 72 US gallons, which confirms the factor is applied the right way round.
How to read your score
Frequently asked questions
How many imperial fluid ounces are in one US gallon?
Exactly 133.2278695. 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 imperial fluid ounces?
Imperial Fluid Ounces = US gallons × 133.2278695. To reverse it, divide instead: US gallons = imperial fluid ounces ÷ 133.2278695, which is the same as multiplying by 0.007505937034.
Is the US gallon bigger than the imperial fluid ounce?
Yes. One US gallon equals 133.228 imperial fluid ounces, so it is the larger unit.
Why does my answer differ slightly from other us-gallons to imperial-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 imperial fluid ounce?
The UK fluid ounce, about 4% smaller than its US counterpart.
Us Gallons to imperial fluid ounces reference table
| Us Gallons | Imperial Fluid Ounces |
|---|---|
| 0.5 gal | 66.6139 fl oz |
| 1 gal | 133.2279 fl oz |
| 2 gal | 266.4557 fl oz |
| 3 gal | 399.6836 fl oz |
| 5 gal | 666.1393 fl oz |
| 10 gal | 1,332.28 fl oz |
| 15 gal | 1,998.42 fl oz |
| 20 gal | 2,664.56 fl oz |
| 25 gal | 3,330.7 fl oz |
| 50 gal | 6,661.39 fl oz |
| 75 gal | 9,992.09 fl oz |
| 100 gal | 13,322.79 fl oz |
| 250 gal | 33,306.97 fl oz |
| 500 gal | 66,613.93 fl oz |
| 1000 gal | 133,227.87 fl oz |
Exact factor: 1 US gallon = 133.2278695 imperial fluid ounces. Values rounded for display.