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Yasso 800s Calculator

Turn your marathon goal into an 800 m repeat time.

How it is calculated

Yasso's rule says the hours and minutes of your marathon match the minutes and seconds of your 800 m repeat. In practice the tool reads your value as decimal hours (or decimal minutes) and treats it as the same number of minutes or seconds: repeat seconds = value × 60 and marathon minutes = value × 60. Repeat pace is repeat time / 0.8 km, marathon pace is marathon time / 42.195 km, and the workout time is 2 × repeat time × number of reps because each repeat is followed by an equal-length jog. Volume is reps × 0.8 × 2 km. Value must be between 1.5 and 7, reps between 1 and 20. Either direction gives the same pair, because the rule is symmetric. This is a rule of thumb, not a physiological formula.

Worked example

Goal marathon 3.5 hours (3:30), 10 repeats. Yasso repeat time: 3:30 per 800 m. Repeat pace: 210 s / 0.8 km = 262 s, about 4:23 /km. Marathon pace: 210 min / 42.195 km = 4:59 /km, so the repeats are run about 36 seconds per km faster. Workout time: 2 × 3:30 × 10 = 70:00 including the jogs. Volume: 10 × 0.8 × 2 = 16.0 km.

Try this example →

Common mistakes

  • Entering 3.30 for a 3:30 marathon. The field is decimal hours, so 3.30 is 3 hours 18 minutes; 3 hours 30 minutes is 3.5.
  • Running the repeats all out. The rule applies when the 10 repeats are evenly paced with equal-length jog recoveries; an extra-fast first few repeats mean nothing.
  • Running fewer repeats and comparing the average time with the full rule. The rule is built on ten; the tool sizes the workout for your reps but the time-to-marathon mapping is the same.
  • Treating the prediction as a guarantee. It is an informal heuristic; weather, course and the long run training behind it still decide the marathon.
  • Expecting a different result from the other direction. Both give the same pair, since the rule maps hours to minutes one-to-one.

About this calculator

Yasso 800s is a marathon-predicting workout popularized by running coach Bart Yasso: run repeated 800 m intervals and note your average time in minutes and seconds, and — according to the rule of thumb — your marathon finish time in hours and minutes will land close to that same number (e.g., ten 800s averaging 3:30 each suggest a marathon around 3 hours 30 minutes). It is an informal, field-tested heuristic rather than a physiological formula, but it has held up well enough across decades of runners to remain a staple marathon-training benchmark.

Marathon runners use it mid-training-cycle as a fitness checkpoint and pacing guide — converting a goal marathon time into a concrete 800 m repeat target tells you exactly what pace to hit in a track workout, and running the workout and converting back tells you where your marathon fitness currently stands. It pairs naturally with marathon-pace runs, since both use the same target number as their anchor.

This calculator converts between a goal marathon time and the matching Yasso 800 repeat pace in either direction, and returns rep pace, marathon pace, and the total time and distance for a full Yasso workout.

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