Running calculator
Yasso 800 calculator
Bart Yasso's marathon workout, both directions: turn a goal marathon time into the 800 m repeats that predict it, or turn the 800s you already run into a marathon time. Free, instant, no sign-up.
10 × 800 m in 3:30, each followed by a recovery jog of the same length — 8 km of fast running and about 1:10:00 on your feet.
One workout is not a plan — the coach builds the twelve weeks around it.
What are Yasso 800s?
Bart Yasso spent decades at Runner's World and noticed a pattern in his own training: whenever he could run ten 800 m repeats at a given minutes-and-seconds, he raced the marathon in the same hours-and-minutes. Ten 800s in 2:50 meant a 2:50 marathon. The session took his name once the magazine printed it, and it has been the most argued-about workout in marathon training ever since.
How this calculator works
The rule is a digit swap, so the arithmetic is exact: minutes become hours and seconds become minutes, and both of those are a factor of sixty. A marathon takes sixty times as many seconds as one repeat — 3:30 per 800 m is 210 seconds, and 210 × 60 is 12,600 seconds, which is 3:30:00. We read it in both directions and print the two paces side by side, because the gap between them is the interesting part: 3:30 repeats are 4:23/km, while the marathon they predict is 4:59/km.
How accurate is it, really?
It is a benchmark, not a physiological model. Nothing in it knows your weekly mileage, and the marathon is decided by exactly the endurance the workout never tests. Thirty years of runners checking it have found the same thing: it flatters people whose speed is ahead of their long runs, and it is closest for runners with a genuine marathon build behind them — high mileage, long runs, and weeks of marathon-pace work. If you hit the 800s but your longest run is 25 km, believe the long runs.
Running the workout
Do it on a track or a flat path in the second half of a marathon block, and treat it as a benchmark rather than a weekly staple — once every three or four weeks is plenty. Build to the full ten: four the first time, then six, then eight. The recovery jog matters as much as the repeat. It is a jog of the same duration, not a walk and not a stand, and shortening it turns the session into something the rule was never calibrated on.