[Avodah] K'zayis as weight not volume?

[Sholom Simon]

>28 ccs of water weighs 28 grams. If something has the same density as
>water and weighs 28 grams, then it has a mass of 28 ccs. Experiments
>have shown that handmade shemurah matzah has approximately half the
>density of water so 14 grams of handmade shemurah matzah has about a
>mass of 28 ccs.

If it's got half the density, then you need twice the weight to get 
an equivalent volume, no?

-- Sholom