Run Time from Distance

Running time vs distance: pace, velocity and Riegel

Time, distance and pace tie together through time = distance / velocity, with velocity being the inverse of pace (min/km). Example: 10 km at 12 km/h → 10 / 12 = 0.833 h = 50 min, the same answer you get from a 5:00/km pace over 10 km. Want to stretch one known time onto other distances? That is where Riegel’s formula comes in: T2 = T1 · (D2/D1)1.06. A 50-minute 10 km projects to a half marathon (21.0975 km) of roughly 50 · (21.0975/10)^1.06 ≈ 1 h 50 min. That 1.06 exponent is there because pace drifts slower as the distance climbs, thanks to fatigue, glycogen depletion and rising body heat. Garmin Connect, Strava and Polar Flow lean on the same logic when they project race times from your training.

Applications: amateur runners, race planning, virtual projections

Amateur runners reach for this when they want to know how long a target distance will take at a given pace. It shows up in training plans for the 5K, 10K, half marathon and marathon, and in the estimated time your GPS watch flashes on screen mid-run. Garmin Race Predictor and Strava Best Efforts run their own takes on Riegel, blending in recent VO2max to sharpen the projection.

FAQ

Does Riegel work for any distance? It is at its best from 5 km up to the marathon. Drop below 1 km and it underestimates; go past 50 km and it overestimates, since ultra running follows a different fatigue curve.

Why doesn’t the pace stay constant when I double the distance? Fatigue piles up and your aerobic capacity has limits. The longer the race runs, the slower your average pace ends up.

Does altitude or heat change the calculation? They do. Count on paces running 1-3% slower for every 1000 m of altitude or each 5 °C above 20 °C. The formula assumes standard conditions.

Are the watch projections reliable? They make a good target to chase, though it takes 4-8 weeks of steady training before they line up with your real fitness.