Race Time Equivalency Calculator
One result, four answers. Enter a race you have run and the calculator prints the equivalent time and pace at 5K, 10K, half marathon and marathon — all from the same Riegel exponent, so the four rows are directly comparable with each other:
Predicted time
52:07
Predicted pace of 5:13/km.
How we got this number
T₂ = T₁ × (D₂ ÷ D₁)^1.06 = 25:00 × (10 ÷ 5)^1.06 = 52:07
| Distance | Predicted time | Predicted pace |
|---|
Worked example: everything from a 25:00 5K
| Distance | Equivalent time | Equivalent pace |
|---|---|---|
| 5K | 25:00 | 5:00/km |
| 10K | 52:07 | 5:13/km |
| Half marathon | 1:55:00 | 5:27/km |
| Marathon | 3:59:47 | 5:41/km |
Read down the pace column and you can watch the fatigue factor work: 5:00, 5:13, 5:27, 5:41. Each step costs a little more, and the marathon row asks for 41 seconds per kilometer less than the 5K that generated it.
The question this table is actually good at
Not “what will I run”, but “which of my races was the best one”. Suppose you have a 52:00 10K and a 2:05 half marathon. Converting the 10K gives an equivalent half of about 1:55 — so the half marathon is the weaker performance by ten minutes, and that is where the training gap is. Runners usually discover the same thing: their short-distance equivalent is faster than their long- distance reality, which points at endurance rather than speed.
Run it the other way too. If your marathon converts into a 5K faster than you have ever actually raced, your top-end speed is the thing that has gone stale.
What equivalency deliberately ignores
Age and sex are not in the equation. Two runners with the same 10K produce the same table whether they are 25 or 60, which is fine for tracking yourself over a season and useless for comparing across a field. Course profile, altitude and weather are absent too — a hilly half converted from a flat 10K will look like an underperformance that never happened.
And the marathon row carries the formula’s known bias: in a study of 2,303 recreational runners, Riegel marathon predictions were at least ten minutes too fast for half of them, while the 10K and half marathon rows held up. Trust the rows near your actual race distance and discount the far ones.
For a single prediction with the reasoning attached, use the race time predictor; for the step-by-step progression, start with the 10K from your 5K.
Frequently asked questions
What is an equivalent race time?
The time at another distance that represents the same level of performance. It lets you ask whether your 10K or your half marathon is the better result, which raw times cannot answer because the distances differ.
How is the equivalent time calculated?
With Riegel's equation applied to each standard distance in turn: T2 = T1 x (D2 / D1)^1.06. One known result produces four rows — 5K, 10K, half marathon and marathon — plus the pace each implies.
Can I use this to compare myself with another runner?
Only if you are comparing like with like. Equivalency ignores age and sex, so a 50-year-old and a 25-year-old with the same 10K look identical here. Age-graded scoring exists for exactly that comparison.
Which row should I actually trust?
The rows nearest the distance you actually raced. Converting a 5K into a marathon crosses the widest gap on the table and inherits the formula's known marathon bias, which runs about ten minutes fast for half of recreational runners.
Do all conversion calculators give the same answer?
No. They differ in the exponent, from about 1.05 to 1.08, and some use fitted models instead. A 2024 benchmark put the plain Riegel formula at 80% accuracy against a purpose-built model's 90%.
Sources
- Vickers AJ, Vertosick EA. An empirical study of race times in recreational endurance runners. BMC Sports Sci Med Rehabil, 2016;8:26
- Dash S. Win Your Race Goal: A Generalized Approach to Prediction of Running Performance. Sports Med Int Open, 2024;8
Written by Lucas Silva · Reviewed by Lucas Silva · Updated on August 15, 2026