Originally Posted by QuiltE

Plays10s ... This link will help you figure this out, and for other times too!

Free Online Graph Paper / Asymmetric and Specialty Grid Paper PDFs (incompetech.com)
Choose Axonometric, then select your desired options.
Or you can use any graph paper (also in link), then turn on point.
You'll then be able to see on paper what KrisB has explained.
Plus, can check out other options you may want to consider.

There's calculators and charts online for the diagonal distance across a block.
However, for me, I find it just as easy, (perhaps simpler?)
to go old school and just measure with a ruler!