Use these sites to help you find your target pace, this can be used as an important training tool
Put your distance in, then put your time in, make sure there is a zero in the hour box. We would always like to see even splits (stay the same pace) or negative splits (get faster each mile).
Race Pace Calculator sorry no 4K info here, you can use the 2 mile infomation
Mcmillan Pace Calculator guys mark 5k and girls mark 4000m
Race Splits, put distance and target time in boxes Race Planner
This next Calculator can be used for speed work. Remember you need to have a good mileage base before you start speed work
If you do not know you Maxium Heart Rate, find it here, you need to put your age and gender in