Convert cups to fl oz US cups ↔ US fluid ounces Free Online Secure
Type a value in US cups and read it in US fluid ounces at once. The factor is exact by definition, the arithmetic happens in your browser, and nothing is sent anywhere.
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Convert from US cups
Convert to US fluid ounces
Common values — Convert cups to fl oz (US cups ↔ US fluid ounces)
| cup | fl oz |
|---|---|
| 1 | 8 |
| 2 | 16 |
| 3 | 24 |
| 5 | 40 |
| 10 | 80 |
| 20 | 160 |
| 50 | 400 |
| 100 | 800 |
Where these units come from
The litre has an awkward history. From 1901 it was defined as the volume of one kilogram of pure water at its densest, which sounds elegant but came out at 1.000028 cubic decimetres — close enough to be confusing and far enough to spoil careful work. In 1964 the definition was abandoned and the litre became exactly one cubic decimetre, which it has been ever since. The gallon has a messier story still: the US gallon descends from the English wine gallon of 231 cubic inches, while Britain redefined its own in 1824 as the volume of ten pounds of water. Nobody reconciled the two, so a US gallon is 3.785411784 litres and an imperial gallon 4.54609 — about a fifth larger. The gallon, pint, cup, fluid ounce and spoons on this page are the US ones.
Where you meet them
Millilitres and litres run through daily life almost invisibly: bottles, fuel, paint, dosage, the capacity of a kettle. Cubic metres belong to water bills, concrete, shipping and the air a ventilation system has to move. Cubic centimetres name engine displacement, cubic feet appear in freight and in appliance capacities, and cups and spoons live almost entirely in recipes — which is exactly where the difference between a US cup and a metric one quietly ruins a cake.
Questions people ask
Are cups and spoons the same everywhere?
No, and this catches people out. The cup used here is the US one, 236.588 ml; a metric cup is 250 ml and an Australian one the same. The tablespoon here is 14.787 ml, while the metric tablespoon is 15 ml and the Australian one 20 ml. For a cake the difference rarely matters, but for yeast, salt or baking powder it does — when a recipe is precise, check whose spoon it means.
Is a fluid ounce a measure of weight?
No, it is a measure of volume, even though ounce also names a weight. A US fluid ounce is 29.5735 millilitres; the imperial one is slightly smaller, at 28.4131. The shared name is a historical accident, and for water the two roughly match, since a fluid ounce of water weighs close to an ounce.
Is the answer exact?
Where both units are defined in terms of one another by whole numbers, yes — the page says so above the figure, and the only rounding is in how many digits are shown. Where the ratio has no finite decimal, the page shows twelve significant digits and says the relation is approximate rather than pretending otherwise.
Does anything I type leave my device?
No. The arithmetic runs in your browser; nothing is uploaded and there is no server to upload it to. Load the page once and it keeps working with the network switched off.
Fluid ounces and weight ounces: the baker's puzzle behind the cup
A cup holds eight fluid ounces, and that is true whatever is in it. But a cup of flour weighs about 4.25 ounces on a scale, and a cup of honey 12. Baking blogs mix the two kinds of ounce all the time, and the confusion ruins more recipes than any oven. To convert cups to fl oz in volume you multiply by 8: 2.5 cups is 20 fluid ounces, and 4 cups is 32. This page multiplies as you type, and the text below untangles volume from weight, with a table of what a cup of common ingredients weighs.
The page covers the rule with examples, a note on each unit, a comparison, a tour of ingredients and the slips to avoid. All arithmetic happens in your browser; nothing you enter is sent anywhere.
How to convert cups to fl oz: multiply by 8
The rule
A US cup holds exactly 8 US fluid ounces. To convert cups to fl oz, multiply the cups by 8. So 1 cup is 8 fl oz, 1.5 cups is 12, 2.5 cups is 20 and 4 cups is 32. In the other direction, divide fluid ounces by 8.
Worked examples
A recipe that wants 3 cups of stock needs 24 fluid ounces. A 12 ounce can of soda is 1.5 cups. A 16 ounce bottle of juice is 2 cups. A half-gallon carton, 8 cups, has 64 fluid ounces. In each case the ounces are of volume.
Why not 16
A pint has 16 fluid ounces and a quart 32. Between a cup and an ounce the factor is 8. Using the pint's 16 doubles the answer.
A quick sanity check
The ounce is the smaller unit, so the number grows eightfold. If your “convert cups to fl oz” calculation result is only twice or four times bigger, you used the wrong factor.
The cup
Eight fluid ounces
The US customary cup is 236.6 millilitres. It measures liquids and, by convention, dry ingredients, which is exactly where the trouble starts, since ingredients differ greatly in density.
Where it appears
Recipes, nutrition labels and measuring cups.
The fluid ounce
A measure of volume
The US fluid ounce is 29.57 millilitres, an eighth of a cup, two tablespoons. It is a unit of volume, and it is not the same as the ounce of weight, 28.35 grams, though for water the two are within 4 percent of each other.
Where it appears
Drink labels, medicine bottles, cosmetics and recipes.
Cup and fluid ounce compared
A cup holds 8 fluid ounces. The trap is that the ounce on a kitchen scale is a different thing. A cup of water weighs 8.3 ounces, close enough to fool people, but a cup of flour weighs about half that and a cup of honey half as much again. The measuring cup counts volume, the scale counts weight.
The factor 8 is exact for volume. For weight, you need the density of the ingredient.
Where the conversion appears
Liquids
For water, milk and stock the cup of 8 fluid ounces weighs about 8.3 to 8.6 ounces. A recipe calling for 2 cups of milk, where you convert cups to fl oz first, needs 16 fluid ounces, which weighs about 17 ounces, 490 grams. Liquids are generally safe to measure in cups, and the number of fluid ounces comes by multiplying by 8, which is what to do when you convert cups to fl oz.
Dry ingredients by weight
A cup of all-purpose flour weighs about 4.25 ounces, 120 grams. Sugar 7 ounces, 200 grams. Brown sugar, packed, 7.5 ounces. Butter 8 ounces, 227 grams. Cocoa 3 ounces. Oats 3.2 ounces. Chocolate chips 6 ounces. These are weights, not fluid ounces, though both use the word ounce.
Syrups and thick liquids
A cup of honey is 8 fluid ounces but weighs 12 ounces, 340 grams. Maple syrup 11.4 ounces. Peanut butter 9 ounces. Oil 7.7 ounces, since it is lighter than water. Whichever the weight, the volume is still 8 fluid ounces, and a measuring cup greased with oil gives clean pours of syrup.
A table of cups in ounces by weight
Here are weights per cup: all-purpose flour 4.25 oz, bread flour 4.5, cake flour 3.9, granulated sugar 7.1, brown sugar packed 7.5, powdered sugar 4.2, butter 8, honey 12, maple syrup 11.4, water 8.3, milk 8.6, oil 7.7, sour cream 8.1, cocoa 3, oats 3.2, rice 6.5. Keeping this table near the oven makes translating recipes between cups and scales straightforward.
Reducing sauces and stocks
Reducing 4 cups of stock, 32 fluid ounces, to 1 cup, 8 ounces, concentrates it fourfold and leaves a sauce. A recipe that asks for reduced wine to 1/2 cup, 4 ounces, starts from about 1.5 cups, 12 ounces. The loss by evaporation is a volume measure, so the cups and fluid ounces work, and you convert cups to fl oz for both the start and the end.
Milk for a household
A household that drinks 4 cups of milk a day, 32 ounces, a quart, uses a gallon, 128 ounces, in four days. A half-gallon lasts two. Labels on the carton give the total in fluid ounces, so a family can calculate how long a carton will last by dividing the ounces by the daily use in ounces, which is the number of cups times eight.
Stock and soup
A soup recipe calling for 6 cups of stock, 48 fluid ounces, can use a carton of 32 ounces and a second of 16. Cartons of broth are sold in 32 ounce quarts and 14.5 ounce cans, 1.8 cups. Three cans make 5.4 cups, 43.5 ounces. Cooks often buy a little more than needed and use the rest for another dish.
Scaling a recipe
Doubling a recipe that needs 1.5 cups, 12 fluid ounces, gives 3 cups, 24 ounces. Halving gives 0.75 cups, 6 ounces. The relationship stays linear, though spices and leavening may not scale perfectly. A cook with a jug marked in ounces can scale without fractions of cups, using eight ounces to the cup as a guide.
In a spreadsheet
Put cups in column A and use =A2*8 in column B. For the reverse, =B2/8. A column with =B2*29.5735 gives millilitres. A table with ingredient weights per cup lets you add a column for ounces by weight with =A2*weight_per_cup. Format with one decimal place, and keep the source column for audit.
Rounding
The factor is exact, so rounding is your choice. Recipes use quarter and third cups, which give 2 and 2.67 ounces. In practice, a jug marked to the nearest ounce is accurate enough. For baking that needs precision, measure by weight to the nearest gram and note the volume as a guide only.
A mental shortcut
Multiplying by 8 is three doublings: 1.5 cups, 3, 6, 12 ounces. 2.5 cups, 5, 10, 20 ounces. For the reverse, three halvings: 20 ounces, 10, 5, 2.5 cups. Cooks do it without thinking when they scale a recipe in the middle of cooking, and it works for any fraction.
Reference values
0.25 cup is 2 fl oz, 0.5 cup is 4, 1 cup is 8, 1.5 cups is 12, 2 cups is 16, 2.5 cups is 20, 3 cups is 24, 4 cups is 32 and 8 cups is 64. If you convert cups to fl oz and land far from this ladder, repeat the multiplication.
Checking by reversing
To make sure your “convert cups to fl oz” calculation result is right, divide it by 8. If 2.5 cups gave 20 fl oz, then 20 divided by 8 returns 2.5. A second check is the size of the answer: it should be eight times larger. Check also that you are comparing volume with volume and not with the weight on a scale.
Salad dressings and marinades
A vinaigrette of three parts oil to one part vinegar, made with 3/4 cup of oil, 6 fluid ounces, and 1/4 cup of vinegar, 2 ounces, gives one cup, 8 ounces, enough for a large salad. A bottle of dressing of 16 ounces holds two such batches. Marinades are measured the same way, and the weight on the label refers to the ounces of weight of the contents.
Why flour is the worst offender
A cup of flour can weigh 4 to 6 ounces depending on how it is scooped. Dipping the cup into the bag packs it down: 5 to 5.5 ounces. Spooning it lightly and levelling gives 4.25. The 25 percent difference decides whether a cake is moist or dry. Professional bakers weigh flour in ounces or grams, and the recipes they publish give weights alongside cups to keep results consistent.
Baby formula and food
Powdered formula is mixed with water by the ounce: typically one level scoop to two fluid ounces. A 6 ounce bottle, three-quarters of a cup, takes three scoops. Instructions differ by brand and the label must be followed exactly, since water and powder must be in the right proportions. The cup is not used for feeding, only the fluid ounce marked on the bottle.
Sauces by the cup
Pasta sauce comes in jars of 24 ounces, three cups, enough for a pound of pasta. A recipe for a large family might want 6 cups, 48 ounces, two jars. Canned tomatoes of 28 ounces, 3.5 cups, are used for soups. When a recipe in cups meets a can in ounces, a calculation checks whether the can is enough, since you can convert cups to fl oz for the recipe.
Homemade cleaners
A cleaning spray of equal parts vinegar and water might be 1 cup of each, 8 fluid ounces each, 16 in total, filling a 16 ounce bottle. A double batch fills a quart, 32 ounces. These recipes call for the volumes in cups, while spray bottles are labelled in ounces, so the conversion is part of every home recipe. Always label the bottle with its contents.
Lemonade and punch for a crowd
Classic lemonade uses 1 cup of lemon juice, 8 ounces, 1 cup of sugar and 6 cups of water, 48 ounces. The batch makes 7 cups, 56 ounces, enough for 7 glasses of 8 ounces. A party of 28 needs four batches, 28 cups, 224 ounces, 1.75 gallons. The tally in ounces gives the shopping list for bottled water or juice.
Water: the one safe bridge
A fluid ounce of water weighs 1.04 ounces, close to 29.57 grams. A cup of water is 237 grams. A pint weighs about a pound, 16.7 ounces, which is the origin of the saying "a pint's a pound the world around", true to within about 4 percent. For water, volume and weight can be swapped, but for nothing else without a density table.
Dry measuring cups and liquid ones
Liquid cups have a spout and a line below the rim, so that liquid does not spill, and are read at eye level. Dry cups are filled to the rim and levelled. A liquid cup used for flour will undercount, because the line is below the top. A dry cup used for water will give fewer than eight fluid ounces if the water is not filled to the brim. Use each tool for its job.
Nutrition labels
Labels give serving sizes in cups and in grams or millilitres. A serving of milk is 1 cup, 8 fluid ounces, 240 millilitres. A serving of cereal may be 3/4 cup, 30 grams. When a label gives both, use the weight for accuracy. For liquids, you can check by multiplying the cups by 8 to get the fluid ounces on the container.
Packaged drinks
A can of 12 fluid ounces holds 1.5 cups. A 16.9 ounce bottle, 500 millilitres, holds 2.1 cups. A 20 ounce bottle holds 2.5 cups, 591 millilitres. A 2 litre bottle holds 67.6 ounces, 8.45 cups. Soft drink and juice labels use fluid ounces, and a recipe for punch needs cups, so the conversion is an everyday task.
Measuring spoons and ounces
A fluid ounce is two tablespoons, six teaspoons. A cup is 16 tablespoons. So 4 tablespoons is a quarter of a cup, 2 fluid ounces. A recipe with 1/3 cup of oil, 2.67 fluid ounces, 5.3 tablespoons, is easy to measure with a jug marked in ounces. Chefs working in small volumes tend to use ounces for convenience.
Gelatin and set desserts
A packet of unflavoured gelatin sets about 2 cups of liquid, 16 fluid ounces, a pint, to a firm gel. A mould of 4 cups, 32 ounces, takes two packets. Jelly recipes give the liquid in cups, and the pack gives the weight in ounces, 0.25 of an ounce per packet. Keeping the two kinds of ounce apart is the only trick, and the first one is the ounce you pour.
Medicine and spoons
Liquid medicine is dosed in millilitres or teaspoons, never in cups. A medicine cup has marks at 5, 10, 15 and 30 millilitres, with equivalent ounces. A fluid ounce is 30 millilitres, a tablespoon 15. A bottle of 8 ounces, a cup, 240 millilitres, contains 16 tablespoons. Use the dosing device that comes with the medicine and follow the label.
More values for convert cups to fl oz
A longer list of conversions
If the value you need is not in the first list, these further conversions may be close enough to read off directly:
- 0.1 cup = 0.8 fl oz
- 0.5 cup = 4 fl oz
- 3 cup = 24 fl oz
- 4 cup = 32 fl oz
- 7 cup = 56 fl oz
- 15 cup = 120 fl oz
- 20 cup = 160 fl oz
- 75 cup = 600 fl oz
- 200 cup = 1,600 fl oz
- 500 cup = 4,000 fl oz
- 2,000 cup = 16,000 fl oz
- 10,000 cup = 80,000 fl oz
Mistakes when you convert cups to fl oz
Confusing fluid and weight ounces
A fluid ounce is a volume, an ounce on a scale is a weight. A cup of flour is 8 fluid ounces but only about 4.25 ounces in weight.
Using the pint factor
A pint has 16 fluid ounces, but a cup only 8. Check which unit you are converting.
Dividing instead of multiplying
The ounce is the smaller unit, so the number grows. If 2.5 cups became 0.31, you divided.
Quick answers
How many fluid ounces are in a cup?
Eight.
How do I convert cups to fl oz?
Multiply by 8.
How many cups are in a fluid ounce?
0.125.
What is 2.5 cups in fluid ounces?
20 fluid ounces.
Does the number I type leave my device?
No, it stays in your browser.
More pages and a closing note
For other volume conversions, see Convert cups to pt, Convert ml to fl oz, Convert L to fl oz, Convert fl oz to ml, Convert km to mi, Convert mi to km, Convert °C to °F, Convert °F to °C, Convert kWh to cal. The opposite direction is Convert fl oz to cups.
In short, you convert cups to fl oz by multiplying by 8 and writing the unit beside the answer. Your figure is calculated on your own device, with no account and no upload.