I’ve had 205/70-14s on the back of my wagon for eight years now, using 14×6 aluminum wheels with a slight negative offset (they are biased towards the outside). Obviously that tire is about an inch smaller in diameter than yours, but it’s the same section width. Scott Phillips has 215/60-15s on the stock 15″ wheels on his convertible and they also fit fine. Again, about an inch smaller in diameter than yours but about 0.4″ wider in section.
As for measuring, well, tires are flexible. Both actual section width and diameter depend on both air pressure and rim width.