Race time predictor
The following link takes you to the RunnersWorld calculator that predicts your race time from another recent race time at a different distance. For example, if you are racing a 10K and have recently run a 5K race you can use the 5K time as a means of predicting your 10K time.
http://www.runnersworld.co.uk/general/rws-race-time-predictor/1681.html
Training pace calculator
The following RunnersWorld calculator provides you with a range of training paces from a recent race time.
http://www.runnersworld.co.uk/general/rws-training-pace-calculator/1676.html
As a general guide, you can quickly calculate paces for workouts and races from your 5K race time.
Long intervals (e.g. Tuesday) — run at 5K pace
Tempo runs (e.g. Tuesday or Thursday continuous) – 5k pace + (30-45 seconds per mile)
Short intervals (e.g. Saturday track) — 5K pace — (10-15 seconds per mile)
Long runs (e.g. Sundays) — 5K pace+(45 seconds — 1:45 minutes per mile)
Easy runs — 5K pace + 1-2 minutes per mile
10K race — 5K pace + (15-20 seconds per mile)
Half marathon — 5K pace +(45 seconds to one minute per mile)
Marathon — Double your half marathon and add 10-20 minutes