ounces vs. fluid ounces

Merrysix

My food scale can be set to grams, ounces and fluid ounces. What is the difference between ounces and fluid ounces when I measure my food? Thanks!

ccsernica

The fluid ounce is a measure of volume, not weight. You measure it with a cup or spoon, not a scale.

Now, 1 fl. oz of water indeed weighs about 1 avoirdupois oz, which is why the measures have the same name, but not everything has the same density as water. And volume is a very unreliable way of measuring solids, even though amounts of powdered or granular solids are often given in volume measures in American cookbooks. It's convenient, but less accurate.

So I have no idea how you can possibly set a scale to measure fluid oz. I'd either consult the manual, which should explain what they're doing, or ignore it.

ElizabethHanrahan

Fluid ounces are for liquids. Liquids weigh different than solids. If you are making a salad dressing or a marinade, you would use the fluid ounce measurement and be sure to use the same fluid ounce for your ingredient in the data base. If you find a solid measure that is in fluid ounces, it is probably not the exact weight that you think. I would try measuring some rice using both ounce functions and see if there is any difference.

seska422

Fluid ounces and milliliters cannot be weighed. They are units of volume.

Water (and liquids with the density of water) can be weighed because 1 gram = 1 milliliter. The further away from the density of water the liquid is, the less accurate the scale "volume" measurement will be.

People would like to be able to weigh items that have their nutritional info listed in fl oz or ml so scale companies have tried to accommodate them by making it look like volumes can be weighed. All that the scale is doing is weighing the item and changing the label from g to ml or converting the oz to the equivalent fl oz that water would have at that weight. The instructions for my scale said something to the effect that the ml and fl oz measurements were only good for water and liquids with the density of water but how many people read the whole instruction booklet?

For the sake of convenience, I will go ahead and weigh some volume items in small amounts (such as salad dressing) but I keep in mind that the number I get is in the ballpark rather than as accurate as possible. I don't weight larger volume amounts of non-water because the inaccuracy would be magnified.

thewindandthework

One of my scales has a fl oz setting as well. It's for fluids with the density of water, and is, in my opinion, completely useless.

I recommend using a volume measuring container marked with fl oz (or ml) for liquids, and a scale to weigh in oz (or g) for solids.