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Convert gal to fl oz
1 gal = 128 fl oz
Type a value in US gallons and the answer in US fluid ounces appears as you go. The conversion is exactly 128 fl oz to the us gallon, and it happens on your own machine — this page asks nothing of a server once it has loaded.
Where it runs
In your browser. The number you type is never part of a request.
Exact by definition
1 gal is exactly 128 fl oz — a definition, not a rounded factor.
Answers as you type
No button, no wait. The worked answer is already on the page before any script runs.
US gallon and US fluid ounce
A US gallon is defined as 231 cubic inches, exactly — a definition that comes from an English wine gallon of 1707. The imperial gallon is 4.55 litres, about 20% larger.
A US fluid ounce is 29.57 ml; a UK one is 28.41 ml. They are different units with the same name, and recipes rarely say which they mean.
US gallons to US fluid ounces in practice
15 gal is 1920 fl oz
— a US car tank, as the pump measures it.
1 gal is 128 fl oz
— a large bottle of milk, as a US shop sells it.
US gallons to US fluid ounces at a glance
| gal | fl oz |
|---|---|
| 1 | 128 |
| 2 | 256 |
| 3 | 384 |
| 5 | 640 |
| 10 | 1280 |
| 20 | 2560 |
| 50 | 6400 |
| 100 | 12800 |
Every figure here is computed from the same definition the calculator uses, so the table cannot drift away from the answer above it.
Convert gal to fl oz: common questions
How many US fluid ounces are in a us gallon?
Exactly 128. One us gallon is 128 US fluid ounces, and the box above will do it for any figure you type.
Is this conversion exact, or rounded?
The ratio is exact. It is not a rounded constant typed into a table: it is derived from the definitions of the two units, so it agrees with any other correct converter to as many digits as you care to compare.
Why does another converter show a slightly different number?
Almost always rounding rather than disagreement. Many converters cut the answer to two or four decimals, and some carry a factor that was rounded before the multiplication rather than after. The figures here are computed from the exact definitions and only rounded on the way to the screen.
Where these figures come from
The claims this page makes about volume units are checkable, and these are the documents that settle them.
How this page works
The factor is a constant in the page and the arithmetic is four operations, so nothing is sent anywhere and nothing needs to be. The number you type never leaves the browser — there is no request for it to travel in.