DW> I think 355 mL is 12 ounces, though whether
 DW> they're "Imperial" fluid ounces (the volume of an ounce
 DW> (mass) of water), or weird Yankee ones, I don't know. The
 DW> Yankee ones are a tad bigger.

It's the weird Yankee ones.

In the US a fluid ounce is 29.573 529 562 5 mL, so 12 fluid ounces
would be about 354.88 mL.

The imperial fluid ounce is 28.413 065 mL, so 12 imperial fluid ounces
would be about 340.96 mL.

In the US an ounce of mass is exactly 28.349 523 125 g.

So if water had a density of 0.998 g/mL (a value found in many textbooks)
then one  imperial fluid ounce of water would have a mass of about one
ounce.

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