The Fresh Loaf

News & Information for Amateur Bakers and Artisan Bread Enthusiasts

Density of water

Dwu3193's picture

Density of water

It seems that a lot of people mistake the density of water for 1 oz./fl. oz.. While it's close to that, it's not quite right, and sometimes people do mistake the density of water and weigh out, say 7 oz. of water when the recipe calls for 7 fl. oz. of water. In imperial system, the density of water is actually 0.9587 oz./fl. oz (moderator's note: see this comment below for disagreement about this number). In metric, water is conveniently 1g/ml (when it's pure, and tap water is close enough to pure for that to be the density) at room temperature. And in case you don't believe me, don't be afraid to bust out your scale and confirm this yourself. Measure out whatever volume of water in ml, and the weight will be the same in grams. However, measure out a certain volume of water in fl. oz., and you'll find that the weight in oz. won't be the same (or weigh it out then measure by volume if you want to be a little more precise).

ClimbHi's picture

I always learned that "a pint's a pound, the whole world round." I guess it's "almost a pound".

Here I was, thinking my measuring cup was just a bit off!

Pittsburgh, PA

LeadDog's picture

I decided that I needed to check the densitometer here at work to see if it needed to be calibrated or not.  The water measured 0.9982 grams/ml at 20 degrees C.  The density of water changes with temperature so I checked my result against the chart on this page  I'm happy with the results.  When I was in school I was taught that the density of water was 1 gram per mL and didn't change much with temperature.  We use the densitometer to determine how many gallons of wine we are shipping so it is important to be accurate.

Stefania's picture

How technical and accurate do we need to be in baking?  Here are the exact densities and, yes, temperature does matter, in analytical chemistry, not in baking.


1 milliliter (ml) = 1 cubic centimeter (cc) of pure water at 4 degrees centigrade - water's densist state (it expands on the phase change of freezing into a solid), so, 1 cubic centimeter contains 1 gram of water at 4 deg. C.


Since Ounces weight (avoirdupois) and Fluid Ounces are actually totally unrelated scales (the term ounce has many meanings) there happens to be a nice accident so that a fluid ounce of water actually weighs 1.0425 ounces avoirdupois.  The source I used did not give temperature so even this is an estimate.


by the way, in the United States we do not use imperial gallons or imperial anything, at lest not since the revolution, we use a scale called avoirdupois I guess the originator of the thread was British?  In avoirdupois the measurement is so close as to be meaningless in the home, not so in the Imperial system.


By the way, a pint of beer in the UK measures around 20 Fluid Ounces in the US.  thats 4 ounces more, lucky Brits.

Stefania (husband half)

chemistDJ's picture

You went the wrong way! The density of water in oz / fl oz is 1.043175365 oz/fl oz!

The value given above (0.9587) is actually fl oz/oz!

Math: 1 g/mL / 28.3495 g/oz * 29.5735mL/fl oz = 1.043175365 oz/fl oz

Read Math: Math: 1 g/mL divided by 28.3495 g/oz times 29.5735mL/fl oz = 1.043175365 oz/fl oz

You can confirm with Google: "1 g/mL in oz/fl oz" returns "1.04318 Ounce / US fluid ounce"