How does DMV or whomever else measure conversion length?

For example, do they take absolute length, or do they disregard thinks like extended front or rear bumpers and such and measure sheet metal of body?

I was reading the NC dmv website last night. Remember it specifically said excluding bumpers.

It will likely vary by state.

If you haven't discovered this web site yet, it's pretty handy: https://www.dmv.org/