I saw this calculator for runners in McMillanRunning. You start by inputting information: the distance you run on average, your best time, mileage, age and gender. Then it’ll make educated estimates on how you’ll probably fair running other distances.

It’ll also give you a list of what pacing you should use in your workout runs, for whatever kind of workout you wish to use, to get the best results possible.

For an example of the results, check this out.