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Running Pace Calculator
Solve pace, time or distance from the other two (km/mi), then predict your 5K/10K/half/marathon times from a recent race with the Riegel formula (T2 = T1 × (D2/D1)^1.06). Even splits + treadmill pace. A fitness estimate — reliable to the half, optimistic beyond. Accurate, instant and free — for United States.
What these mean:
What these mean:
Riegel race predictor
Enter a recent race — its predicted times for 5K, 10K, half and marathon appear in the results.
5:00 per km (5:00/km). Riegel from your 25:00 over 5 km: 10K ≈ 52:07, half ≈ 1:55:00, marathon ≈ 3:59:47. An estimate — reliable to the half, optimistic beyond; general fitness guidance.
Pace / km
5:00 /km
Pace / mi
8:03 /mi
Time
25:00
| Race | Predicted time (Riegel) |
|---|---|
| 5K | 25:00 |
| 10K | 52:07 |
| Half | 1:55:00 |
| Marathon | 3:59:47 |
How far to trust a Riegel prediction
Even splits
At 5:00/km (8:03/mi), every kilometre takes the same time — so an even-paced 5 km comes in around 25:00. Many runners aim for a slight negative split — running the second half a touch faster — rather than dead-even pacing.
An estimate — general fitness guidance
How we calculate this
Reviewed by Reckonist Editorial · Last reviewed July 2026. Figures follow the methods and sources set out in our editorial standards.
Pace = time ÷ distance; race prediction via Riegel (T2 = T1 × (D2/D1)1.06). An estimate — general fitness guidance, not a guaranteed race time.
Riegel 1981 · calculator.net · 1 mi = 1.609344 km
Pair your pace with effort: set training zones with the Heart-Rate Zone Calculator, and estimate the energy cost with the Calories-Burned Calculator.
Pace = time ÷ distance (solve any of the three)
Pace is just time ÷ distance. Give the calculator any two of pace, time and distance and it solves for the third, in km or miles. Every figure carries its unit, and pace is shown as minutes:seconds per km and per mile.
Pace / time / distance
3-way solve
pace = time / distance · time = pace × distance · distance = time / pace
1 mile = 1.609344 km, so 5:00 /km ≈ 8:03 /mi. Keep pace and distance in the same unit.
Riegel predictor
race times across distances
T2 = T1 × (D2 / D1)^1.06
Project a recent race to 5K / 10K / half / marathon. Reliable to the half; optimistic beyond.
- 1Pace: 25:00 ÷ 5 km = 5:00 /km; ÷ 3.107 mi = 8:03 /mi.
- 2Riegel 10K: 25:00 × (10 / 5)1.06 = 25 × 21.06 ≈ 52:07 (half ≈ 1:55, marathon ≈ 3:59 — optimistic beyond the half).
Predict race times from one recent race
Most general pace calculators stop at time ÷ distance. The wedge here is the Riegel race predictor: enter one recent race and it projects your 5K, 10K, half-marathon and marathon times using T2 = T1 × (D2 / D1)1.06. It answers the question runners actually ask — “what marathon can I run off my 5K?”
How far to trust it — the honest caveat
Even splits and the negative-split tactic
An even split means running every km (or mile) in the same time: at 5:00/km, a 10K is 10 × 5:00 = 50:00. It is the simplest way to pace a race and the default the calculator shows. Many runners go one step further with a negative split — running the second half about 1–3% faster than the first — which tends to beat starting too fast and fading in the closing kilometres.
km ↔ mi and treadmill pace
One mile is 1.609344 km, so the same effort is a smaller number in min/km than in min/mi — 5:00/km ≈ 8:03/mi. To turn a treadmill speed into pace, divide 60 by the speed: 12 km/h → 60 ÷ 12 = 5:00/km, and 7.5 mph → 60 ÷ 7.5 = 8:00/mi. Flip the distance-unit toggle and the pace, splits and predictions all switch units with it.
Treadmill vs road
Frequently asked questions
Pace is simply time divided by distance. Run 5 km (a 5K) in 25:00 and your pace is 25 minutes ÷ 5 km = 5:00 per km, which is the same as 8:03 per mile (since 1 mile = 1.609344 km). This calculator solves any one of pace, time or distance from the other two — pick what you want on the "Solve for" toggle, enter the other two, and choose km or mi.
Use the Riegel formula: T2 = T1 × (D2 ÷ D1)^1.06, where T1 is your recent race time over distance D1 and D2 is the target distance. From a 25:00 5K, a 10K is about 25 × (10/5)^1.06 ≈ 52:07, a half-marathon about 1:55, and a marathon about 3:59. Enter your recent race in the Riegel predictor and the 5K/10K/half/marathon projections appear automatically. Treat the marathon number as optimistic — see the accuracy note below.
Riegel predictions are reliable from about a mile up to the half-marathon, and get optimistic beyond it — the marathon projection in particular assumes you have done the specific endurance training for that distance. The prediction is most trustworthy when your input race is at least half the target distance. It is a fitness estimate and a training target, not a guaranteed finish time.
Even splits means covering each kilometre (or mile) in the same time — at 5:00/km, every km takes 5:00, so a 10K comes in around 50:00. Many runners actually aim for a slight negative split, running the second half a touch (1–3%) faster than the first, which tends to produce better race results than starting too fast and fading. The calculator shows your even-pace time; a negative split is an opt-in racing tactic.
One mile is 1.609344 km, so a min/km pace is a smaller number than the same effort in min/mi: 5:00/km ≈ 8:03/mi. To convert a treadmill speed in km/h or mph to pace, divide 60 minutes by the speed — 12 km/h is 60 ÷ 12 = 5:00/km; 7.5 mph is 60 ÷ 7.5 = 8:00/mi. Switch the distance-unit toggle to km or mi and the pace is shown in that unit.
No. Pace maths (time ÷ distance) is exact, but a predicted race time is an estimate — it assumes adequate training and endurance for the distance, good pacing, and race-day conditions. Use it as a realistic target to pace against, not a promise. This is general fitness guidance, not medical advice.
Method, formulas & references
Methodology: pace = time ÷ distance (solve any of the three). Race prediction via the Riegel formula T2 = T1 × (D2 / D1)^1.06 (Riegel 1981), across 5K, 10K, half-marathon (21.0975 km) and marathon (42.195 km); the exponent varies ≈ 1.04 (advanced) to 1.08 (beginner). Units convert with 1 mile = 1.609344 km. All calculations run client-side and nothing is stored. A fitness estimate — reliable to the half, optimistic beyond; a predicted race time assumes adequate training. General fitness guidance, not medical advice.
Cross-links
How we calculate this
Reviewed by Reckonist Editorial · Last reviewed July 2026. Figures follow the methods and sources set out in our editorial standards.
Pace is computed as time ÷ distance; race times are projected with the Riegel formula (T2 = T1 × (D2 / D1)1.06). This is a general fitness estimate — reliable up to the half-marathon and optimistic beyond it, and a predicted race time assumes adequate training and endurance. General fitness guidance, not medical advice.
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