I just recently replaced the cables on my road bike. As opposed to cutting a cable prior to installation, I first installed the housing, then installed the full length of the cable, and then cut the cable and crimped on the cap. This way you won't make a measurement mistake.
Also, I had a pair of wire cutters that could cut the cables, but not the housing. So, I first measured the housing and then cut it with a Dremel tool with a cut-off disk installed.
I had already started the job one night after work and wanted to get it done the same night (after the LBS had closed). The Dremel tool worked, but in hindsight I would have felt better using a pair of cable/housing cutters that were made for the job.