Running Pace Calculator
Calculate running pace, time or distance — enter any two and get the third — with split tables for the standard race distances.
The unit dropdown does not convert anything, and that is correct
Three quantities, one equation: time = pace × distance. Distance is in some unit and pace is per that same unit, so the unit cancels and never appears in the sum. Switching from miles to kilometres does not need to touch the numbers, because 26.2 units at 9:09 per unit is four hours whatever a unit happens to be. That is why the dropdown only rewrites the labels. It looks like an oversight and it is the opposite — a calculator that silently rescaled your distance when you changed a label would be the bug. What it does mean is that you have to be consistent. Enter a distance in kilometres and a pace in minutes per mile and the answer is meaningless, and nothing in the arithmetic can detect it.
A marathon is 26.2188 miles or 42.195 kilometres, so the same four-hour finish is 9:09 per mile or 5:41 per kilometre — two different numbers differing by exactly 1.609344, arrived at without the calculator ever knowing which one you meant.
The second you round away is 13 seconds at the finish
Pace is displayed to the whole second, which is the only sensible way to show it. Over a marathon that is 26.2188 miles of accumulation. Solving for pace and multiplying it back out, across every finish time from two hours to six — 14,401 of them — the mean error is 6.6 seconds and the worst is 13.1. And the worst case is exactly the bound you would predict: half a second of pace, the most rounding can hide, times 26.2188 miles is 13.1 seconds. The measurement lands on the arithmetic rather than near it, which is the sign nothing else is going on.
| Race | Distance | One second per mile costs |
|---|---|---|
| Marathon | 26.22 mi | 26.2 s |
| Half marathon | 13.11 mi | 13.1 s |
| 5K | 3.11 mi | 3.1 s |
So a pace you can only read to the second is precise enough for a parkrun and not for a marathon target, which is why serious plans are written as splits rather than a single number.
A four-hour marathon and a two-hour half need identical pace
The targets people actually aim at, in both units:
| Target | Per mile | Per kilometre |
|---|---|---|
| Sub-3 marathon | 6:52 | 4:16 |
| Sub-4 marathon | 9:09 | 5:41 |
| Sub-5 marathon | 11:27 | 7:07 |
| Sub-2 half marathon | 9:09 | 5:41 |
| Sub-25 5K | 8:03 | 5:00 |
Note the two that match. A four-hour marathon and a two-hour half both need 9:09 a mile, to the second — not a coincidence in the interesting sense, since a marathon is exactly twice a half and four hours is exactly twice two, but it is the reason so many runners use a two-hour half as the check on a four-hour marathon plan. The two targets are literally the same number, so the half tells you whether the pace is there before you commit to holding it for another 13.1 miles.
How to use
- Enter any two of pace, time and distance.
- Read the third value.
- Check the split table for your target race.
- Set a realistic pace from recent race results.
Frequently asked questions
What is pace and how does it differ from speed?
Pace is time per unit of distance — minutes per kilometre or per mile — while speed is distance per unit of time. Runners use pace because it is directly actionable: you can hold a pace on a watch, whereas converting a speed into what to do next requires arithmetic mid-run.
How do I predict a race time from a shorter distance?
Prediction formulas such as Riegel's relate times across distances using an exponent that accounts for the slowdown over longer races. They work reasonably well from 5K to half marathon, and tend to be optimistic for the marathon, where endurance and fuelling matter as much as speed.
What are negative splits?
Running the second half of a race faster than the first. It is the pattern behind most well-executed distance races and the majority of records, because starting conservatively preserves the capacity to finish strongly. Going out too fast is the commonest race-day error by a wide margin.
How much slower is a marathon than double a half?
Considerably more than double the time, for almost everyone. A common guide is roughly double the half-marathon time plus ten to twenty minutes, though it depends heavily on training volume and fuelling. Doubling the half time exactly is a target very few people meet.
Does terrain affect pace much?
Substantially. Hills, trails, wind and heat all cost time, and grade-adjusted pace exists precisely because raw pace is not comparable between a flat road and a hilly trail. Effort is the more consistent measure across varied terrain.
Should I train at my race pace?
Only for part of the time. Most established training approaches spend the large majority of mileage at an easy conversational pace, with a small proportion at or above race pace. Running every session at race effort is a reliable route to fatigue and injury rather than improvement.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.