Pace is total time divided by distance. A 5 km run in 25 minutes is 5:00 per kilometer, which is 8:03 per mile. Race predictions assume you hold the same pace for the whole distance, which gets harder the longer the race, so treat the half marathon and marathon figures as best-case estimates.
Many recreational runners finish a 5K in 25 to 35 minutes, which is a pace of about 5:00 to 7:00 per kilometer (8:03 to 11:15 per mile).
Multiply the pace per kilometer by 1.609. A 5:00 per km pace is 8:03 per mile.
A 4:00:00 marathon (42.195 km) needs about 5:41 per kilometer, or 9:09 per mile.
See also: KM/H to MPH Converter · Hours Calculator · BMI Calculator