To run a half marathon in 1:20, hold 6'06" per mile, i.e. 9.83 mph (3'48"/km). At that pace: 5K in 18'58", 10K in 37'55", half marathon in 1h20'00", marathon in 2h40'00".
Half marathon in 1:20: 6'06"/mile
1 track lap = 1'31"0
1 track lap = 1'31"0
To run a half marathon in 1:20, hold 6'06" per mile, i.e. 9.83 mph (3'48"/km). At that pace: 5K in 18'58", 10K in 37'55", half marathon in 1h20'00", marathon in 2h40'00".