Ounces to Cups

What this converts, and what it cannot

This page converts fluid ounces to cups and back. Both are units of volume, so the conversion is a single exact division and the substance in the container never enters into it.

What it cannot do is take an ounce off a scale. That is a weight, and the whole point of the section below is that a weight has no fixed relationship to a cup. The word ounce is doing two different jobs, and this tool only does one of them. If the number you have came from a scale rather than a measuring jug, the answer this page gives will be wrong for your ingredient unless that ingredient happens to be water.

Working it out by hand

The divisor is a definition, not a measurement. The US customary cup is defined as 8 US fluid ounces, so the conversion is exact and carries no rounding of its own.

Chaining the definitions gives the metric size too. One US fluid ounce is exactly 29.5735295625 mL, so one cup is 8 × 29.5735295625 = 236.5882365 mL. That figure is exact rather than rounded, and it is where the familiar 236.59 mL comes from.

Fluid Ounces vs. Dry/Weight Ounces

It is critical to distinguish between fluid ounces (fl oz) and dry ounces (oz). Fluid ounces measure liquid volume (space), and 1 US cup is always exactly 8 fluid ounces of any liquid. Dry ounces measure weight (heaviness), meaning the weight of a cup varies based on ingredient density. For example, 1 cup of all-purpose flour weighs approximately 4.25 ounces, whereas 1 cup of granulated white sugar weighs approximately 7 ounces. Always verify whether your recipe requires liquid volume or dry weight!

How to convert fluid ounces to cups

To perform the conversion manually, use the formula cups = fl oz ÷ 8. For example, to convert 100 fluid ounces into cups, multiply 100 by 0.125, yielding 12.5 cup.

How to convert cups to fluid ounces

To reverse the conversion, use the formula fl oz = cups × 8. For instance, if you have 10 cups, divide 10 by 0.125 (or multiply by its reciprocal 8), which equals 80 fl oz.

Weight to cups is a different question

This is worth separating out, because it is the request this page most often receives and the one it cannot answer. Asking how many cups are in 8 ounces of flour is not a unit conversion at all. It is a density question, and it has a different answer for every ingredient.

A cup is a fixed volume. What that volume weighs depends entirely on what is in it, and for dry goods it also depends on how the cup was filled: flour spooned in loosely and flour scooped and packed can differ by a fifth or more for the same nominal cup. That is why recipe writers who care about precision give weights in grams rather than cups, and why no single ounces-to-cups number can be right for both flour and sugar.

If your figure came from a scale, what you need is a table for that specific ingredient, not a converter. If it came from a measuring jug or a bottle label, it is a fluid ounce and this page is the right tool.

Edge cases

• Ounce means two different things. Fluid ounce is a volume, and this page converts it. The avoirdupois ounce is a weight, and it cannot be converted to cups without an ingredient density.
• The cup here is the US customary cup. It is defined as 8 US fluid ounces, which is 236.5882365 mL. Recipes from other countries may mean a different volume by the word cup, so check the source before trusting a conversion across regions.
• A nutrition label cup is 240 mL, not this one. US labelling runs off a separate reference-amounts table, in which the FDA pairs 240 mL with the household measure “1 cup”. That is about 1.4% larger than the customary cup converted here.
• A drinking mug is not a cup. A measuring cup is a defined unit; a mug is whatever size it happens to be, often 10 to 12 fluid ounces.
• The division is exact. Dividing by 8 introduces no rounding, because one eighth terminates in decimal. Any imprecision in your answer came from your input or from the display, not from the conversion.
• Density never enters into it. Both sides are volumes, so oil, water and syrup all convert identically. The moment a weight is involved that stops being true.

Your figures stay in the page

The values you enter are processed by this page in your browser. They are not sent to a server, not stored after you close the tab, and not visible to anyone else. There is no account and nothing to sign up for.

Sources

The division by 8 needs no authority: the US customary cup is defined as 8 US fluid ounces. What the citations below support is the metric size of those units, which is where an outside body actually settles something.

• NIST Special Publication 811, Appendix B.9, which gives the inch as exactly 2.54 cm. With the US liquid gallon of 231 cubic inches in NIST Handbook 44, Appendix C, and 128 fluid ounces to the gallon, this fixes the US fluid ounce at 29.5735295625 mL and therefore the cup at 236.5882365 mL.
• 21 CFR 101.12, reference amounts customarily consumed per eating occasion, where the FDA pairs a 240 mL reference amount with the household measure written as “1 cup (240 mL)”. Cited only for that pairing: it is a labelling convention and not a redefinition of the customary cup.

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