This converter turns US fluid ounces into imperial fluid ounces instantly, using the exact factor 1 US fluid ounce = 1.040842731 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.
One eighth of a US cup, roughly 29.57 millilitres. 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 fluid ounces- The amount you are converting, measured in US fluid ounces
1.040842731- The exact number of imperial fluid ounces in one US fluid ounce
imperial fluid ounces- The converted result
How it works, step by step
- Enter the number of US fluid ounces you want to convert.
- The value is multiplied by 1.040842731, 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 fluid ounces
Multiply 5 by 1.0408427. That gives 5.2042 imperial fluid ounces. A quick sanity check: one US fluid ounce is larger than one imperial fluid ounce, so the number should get bigger — and it does.
Converting 72 US fluid ounces
72 × 1.0408427 = 74.9407 imperial fluid ounces. Working backwards, 74.9407 ÷ 1.0408427 returns 72 US fluid ounces, 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 fluid ounce?
Exactly 1.040842731. 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 fluid ounces to imperial fluid ounces?
Imperial Fluid Ounces = US fluid ounces × 1.040842731. To reverse it, divide instead: US fluid ounces = imperial fluid ounces ÷ 1.040842731, which is the same as multiplying by 0.9607599404.
Is the US fluid ounce bigger than the imperial fluid ounce?
Yes. One US fluid ounce equals 1.04084 imperial fluid ounces, so it is the larger unit.
Why does my answer differ slightly from other us-fluid-ounces 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 fluid ounce?
One eighth of a US cup, roughly 29.57 millilitres.
What is a imperial fluid ounce?
The UK fluid ounce, about 4% smaller than its US counterpart.
Us Fluid Ounces to imperial fluid ounces reference table
| Us Fluid Ounces | Imperial Fluid Ounces |
|---|---|
| 0.5 fl oz | 0.520421 fl oz |
| 1 fl oz | 1.0408 fl oz |
| 2 fl oz | 2.0817 fl oz |
| 3 fl oz | 3.1225 fl oz |
| 5 fl oz | 5.2042 fl oz |
| 10 fl oz | 10.4084 fl oz |
| 15 fl oz | 15.6126 fl oz |
| 20 fl oz | 20.8169 fl oz |
| 25 fl oz | 26.0211 fl oz |
| 50 fl oz | 52.0421 fl oz |
| 75 fl oz | 78.0632 fl oz |
| 100 fl oz | 104.0843 fl oz |
| 250 fl oz | 260.2107 fl oz |
| 500 fl oz | 520.4214 fl oz |
| 1000 fl oz | 1,040.84 fl oz |
Exact factor: 1 US fluid ounce = 1.040842731 imperial fluid ounces. Values rounded for display.