Here are some tools to help you out with those pesky calculations
Splits based on marathon time
Enter finish time in H:MM format
Conversion between pace and speed
Press + or - keys to adjust the increments
Run paces, enter target marathon time
Approx paces, to be used as a guide
Adjusting your time for various conditions
Set off at an easier pace
Weight Convertor
Enter kg value
Marathon Predictor
Enter time for 5K, 10k or half marathon
Nutrition Requirements
Approximations, test in training
Marathon Splits
Various ways to get to the finish