Asked by Mystery Runner
The half marathon should be run at or just below your lactate-threshold pace which is a pace that you should be able to hold for at least an hour or more.
To find out what your LT pace is, you can run a 5k race or even just do a 2 mile time trial, however, I believe a race is more indicative of what you are capable of then just doing a time trial on your own.
Once you have your 5k time, use a running calculator such as the McMillan Running Calculator or runbayou.com to find out what your threshold pace though be. Use the pace you found as a good starting point. For example, lets say you ran a 5k in 19 minutes flat, if you enter that time into the McMillan calculator, it tells you that you should be able to run a 1/2 marathon in 1:27:50. It also tells you that your tempo pace (or LT pace) should be between 6:26 and 6:43 per mile.