An imperial fluid ounce is 1⁄20 of an imperial pint, 1⁄160 of an imperial gallon or exactly 28.4130625 mL.
A US customary fluid ounce is 1⁄16 of a US liquid pint and 1⁄128 of a US liquid gallon or exactly 29.5735295625 mL, making it about 4.08% larger than the imperial fluid ounce.
A US food labeling fluid ounce is exactly 30 mL.
So we have 28.4g, 29.6g or 30g of water. An ounce is 28.3g (closest to the imperial measures and neither of the US ones, despite the ounce being common to imperial and US systems)
I’d consider that within the margin of error for a volumetric measurement. Especially if you are being lazy like me and measuring something like milk by weight.
Funny enough, you made me go check my kitchen scales. They report in grams, ounces, and weirdly milliliters and fluid ounces. I used my scale that reports in hundredths of a gram to measure out exactly 1 oz mass. I then placed it on my other three scales to see what it would read. 2 of them correctly reported that they weren’t quite at 1 fluid ounce, while the other said it was. I never actually put my scales in ounce mode, though.
Except that’s not true.
So we have 28.4g, 29.6g or 30g of water. An ounce is 28.3g (closest to the imperial measures and neither of the US ones, despite the ounce being common to imperial and US systems)
I’d consider that within the margin of error for a volumetric measurement. Especially if you are being lazy like me and measuring something like milk by weight.
Funny enough, you made me go check my kitchen scales. They report in grams, ounces, and weirdly milliliters and fluid ounces. I used my scale that reports in hundredths of a gram to measure out exactly 1 oz mass. I then placed it on my other three scales to see what it would read. 2 of them correctly reported that they weren’t quite at 1 fluid ounce, while the other said it was. I never actually put my scales in ounce mode, though.