The short answer is that we are probably 8 grams or so (about 4%) light on our cup of water or milk to grams / ounces of water conversion, John. This is about 1 1/2 teaspoons by volume. The US Customary Ounce is a measure of volume, about 29.6 ml.
Since a ml of water weighs a gram (by definition), a US Customary Ounce of water weighs about 29.6 grams.
​An ounce as a measure of weight is 28.35 g.
So yes, in converting the weight of our 8 US Customary Ounce cups of water and milk we use a conversion factor that is about 4 % too small.

That being said;
a. Our recipes are tested by volume and weight before being published to ensure they work either way.
b. The density of our other ingredients were determined empirically, so there’s not even a chance of this small 4% error there.
c. 4% is within most people’s volume measurement error.
d. “A pint’s a pound the world around” is something lots of people go by, which is true if you’re using the Imperial Ounce, another volume measure that is 28.4 ml (grams of water), but we are using US made volume measuring cups.

We hope this helps clarify.

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