How it works
5K pace = mile + 33 s; 10K ×1.15; 10 mi ×1.175; half ×1.2; marathon ×1.3
Each projected race pace is your mile time adjusted by a fixed, distance-specific amount that Galloway fitted over decades of coaching data. For the 5K you add 33 seconds per mile; the 10K multiplies the mile time by 1.15, ten miles by 1.175, the half by 1.2, and the marathon by 1.3 — the factors grow with distance because pace inevitably fades as races get longer. The calculator then multiplies each per-mile pace by the distance to produce a finish time. Run a 7:00 magic mile, for instance, and the model projects about a 23:27 5K and a marathon in the neighborhood of 3:58, at 9:06 per mile. One mile is all the model sees, so the long-distance projections assume the endurance work is actually in your legs.
Sources
- Galloway Magic Mile Jeff Galloway, “Magic Mile” (jeffgalloway.com) — race-prediction factors from a one-mile time trial: 5K = mile + 33 s, 10K ×1.15, 10 mi ×1.175, half ×1.2, marathon ×1.3.
- Field-test prediction Short time-trial tests estimate race potential from current speed; Galloway’s factors are empirical, fitted across hundreds of thousands of runners.
- Endurance fade with distance Race pace slows predictably as distance grows — the basis for the increasing multipliers from 5K to the marathon.
FAQ
When should I run a Magic Mile test?
Early in a training block to set starting paces, then again every few weeks to track the trend. Because the test is only a mile, it costs far less recovery than a tune-up race, so you can repeat it often — on the same stretch of road or track, in similar conditions — and watch the projections move as fitness builds.
How should I run the mile itself?
Warm up thoroughly — ten minutes of easy jogging plus a few strides — then run one measured mile at the fastest pace you can hold evenly. Going out in a sprint and crawling home spoils the test. A 400 m track (four laps plus 9 meters) or a GPS-verified flat road segment both work.
How should I read the projections?
As ceilings you can train toward, not times you are owed. The 5K number is usually within reach off mile speed alone; the half and marathon projections assume you have built the long-run endurance to hold the pace, and they presume decent weather and a fair course.
Does this work if I train in kilometers?
The test itself is defined over one mile — that is the distance Galloway’s factors were fitted to — so run the trial over a full mile rather than 1500 m or 1600 m. The projections are plain finish times and per-mile paces, so metric-minded runners can convert the pace to per-kilometer targets afterward.
Why is the marathon factor so much bigger than the 5K adjustment?
Endurance fade. Nobody holds mile pace for 26.2 miles; the further you race, the more you must back off, and Galloway’s multipliers encode that curve. Adding 33 seconds covers the drop from a mile to a 5K, while the marathon needs the full 1.3 multiplier — for a 7:00 miler, that is about two minutes per mile slower than the trial.
How does the Magic Mile compare with VDOT or Riegel?
They come from different data. Galloway fitted fixed factors to a huge coaching population, while VDOT models running physiology and Riegel fits a power law to race results. When a Magic Mile projection and a VDOT projection agree, trust the goal; when they split, the truth usually sits between them, leaning toward whichever test effort was more recent.
Magic Mile projections apply fixed coaching factors to a single one-mile effort, so they describe potential, not promises — especially at the half marathon and marathon, which demand endurance a mile test cannot measure. Use them to frame training goals; they are not medical advice or a substitute for a coach who knows your history.