Marathon Time from a Half
Doubling the distance takes a little more than double the time. Riegel’s formula puts that “little more” at two to the power 1.06, so a 1:45 half predicts about 3:39 for the full.
Your numbers
Marathon prediction
218.9min
Pace
5.19min/km
Difference
8.9min
What it means
Predicted finish around 3 h 39 min, at 5.19 min per kilometre.
Formula
Marathon prediction = Half time (min) × 2 ^ 1.06
It cannot see the wall past 30 km, so undertrained runners finish far later than predicted. Trust it only with solid long-run mileage behind you.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Half time (min) (min)Your finish time over the 21.0975 km half marathon. | 105 | 50 ~ 300 |
Step by step
Quick reference table
Results when only Half time (min) (min) changes and everything else stays put.
| Half time (min) (min) | Marathon prediction (min) | Pace (min/km) | Difference (min) |
|---|---|---|---|
| 52.5 | 109.5 | 2.59 | 4.5 |
| 78.8 | 164.3 | 3.89 | 6.7 |
| 105 | 218.9 | 5.19 | 8.9 |
| 158 | 329.4 | 7.81 | 13.4 |
| 210 | 437.8 | 10.38 | 17.8 |
What each result means
| Result | At default values |
|---|---|
| Marathon prediction (min)Predicted time over 42.195 km at the same fitness. | 218.9 |
| Pace (min/km)The minutes part of the time per kilometre. | 5.19 |
| Difference (min)The gap between two values — a quantity, not a rate. | 8.9 |
Common mistakes
It cannot see the wall past 30 km, so undertrained runners finish far later than predicted. Trust it only with solid long-run mileage behind you.
Glossary
- Half time (min)
- Your finish time over the 21.0975 km half marathon.
- Marathon prediction
- Predicted time over 42.195 km at the same fitness.
- Pace
- The minutes part of the time per kilometre.
- Difference
- The gap between two values — a quantity, not a rate.
Frequently asked questions
Q. How is Marathon Time from a Half calculated?
Marathon prediction = Half time (min) × 2 ^ 1.06 — Doubling the distance takes a little more than double the time. Riegel’s formula puts that “little more” at two to the power 1.06, so a 1:45 half predicts about 3:39 for the full.
Q. Can you walk through an example?
With Half time (min) 105min, the answer is Marathon prediction 218.9min.
Q. What do I need to enter?
Enter Half time (min). The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Half time (min) (min) moves the answer to Half time (min) (min) 52.5 → Marathon prediction (min) 109.5 and Half time (min) (min) 210 → Marathon prediction (min) 437.8. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
It cannot see the wall past 30 km, so undertrained runners finish far later than predicted. Trust it only with solid long-run mileage behind you.
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