Enter any two of distance, time and pace to calculate the third — plus get predicted finish times for 5K, 10K, half marathon and marathon from your current fitness.
Divide your total time in minutes by the distance. For example, 50 minutes for 10 km = 5:00 min/km. This calculator does it instantly and converts between min/km and min/mile.
Most beginners run 6:30–8:00 min/km (10:30–13:00 min/mile). Consistency matters more than speed — build distance first, speed follows.
Predictions use the Riegel formula (time × (new distance ÷ old distance)^1.06), the standard runners use. They assume similar training and conditions.
Multiply min/km by 1.609. So 5:00/km ≈ 8:03/mile. This calculator converts automatically.
Divide 60 by your pace in decimal minutes: 60 ÷ 6.0 = 10 km/h for a 6:00/km pace, or 60 ÷ 5.5 ≈ 10.9 km/h for 5:30/km. Treadmills usually display speed, so this conversion tells you which treadmill setting matches your outdoor target pace.
Fatigue compounds with distance — the Riegel formula's 1.06 exponent models exactly this. Your body cannot hold 10K intensity for 42.2 km, so the prediction discounts your pace. If anything, undertrained runners slow down even more than the formula predicts.
About 60–90 seconds per kilometre slower than your 5K race pace — a conversational effort where you can speak in full sentences. Most beginners run easy days too fast and hard days too slow; slowing the easy runs is the fastest way to improve.
Runners talk in pace (time per distance, e.g. minutes per kilometre) rather than speed, because pace tells you directly what your watch should show. The core relationship is simple: pace = total time ÷ distance, and its inverse, speed = distance ÷ total time. Every prediction and conversion on this page flows from those two.
Pace: a 10 km run in 55 minutes gives 55 ÷ 10 = 5:30 per km. Unit conversion: multiply min/km by 1.60934 to get min/mile — 5:30/km × 1.60934 ≈ 8:51 per mile. Speed: 10 km in 55 minutes = 10 ÷ (55÷60) ≈ 10.9 km/h; equivalently, speed = 60 ÷ pace-in-minutes (60 ÷ 5.5 = 10.9). Race prediction (Riegel formula): T2 = T1 × (D2 ÷ D1)1.06. A 55:00 10K predicts a marathon of 55 × (42.2 ÷ 10)1.06 = 55 × 4.602 ≈ 253 minutes ≈ 4:13.
The 1.06 exponent is the honesty factor: it captures that you slow down as distance grows, which is why doubling the distance more than doubles the time. Riegel assumes equivalent training — a 10K time will not predict a marathon you have not trained for; undertrained runners fade far worse than the formula says. And pace yourself in-race: start the first kilometre 10–15 seconds slower than target pace. Banking time early almost always backfires; even splits or a slight negative split produce the fastest finish.
The calculator gives you a target pace; race day is about holding it. The data is unambiguous: even or slightly negative splits (second half equal to or faster than the first) produce faster finishes than going out hard and fading. Starting even 10–15 seconds per kilometre faster than target pace in the excitement of kilometre 1 creates an oxygen debt you repay with interest later — most personal bests are run with metronomic discipline through the middle kilometres and a kick at the end. Practise this in training with progression runs (each kilometre slightly faster), and set your watch to show current pace plus average pace so deviations are visible instantly. The fittest runner who paces badly loses to the slightly less fit runner who paces perfectly.
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