Pace is the runner’s exchange rate: minutes per kilometer or mile, the number that converts between a goal time and what you must actually hold, stride after stride. Every race plan, treadmill session, and “can I break four hours” question reduces to pace arithmetic, and most of it is simple division dressed in time formats that make mental math annoying. This guide covers the conversions, race predictions, and training paces, and our free pace calculator does the time-format wrestling for you.
In this guide
Pace, speed, and the three-way conversion
Three quantities lock together; fix any two and the third follows:
- pace = time / distance (minutes per km or mile)
- speed = distance / time (km/h or mph), the inverse of pace: 60 / pace-in-minutes
- finish time = pace × distance
The annoyance is purely notational: pace lives in minutes-and-seconds, so 5.5 min/km must be read as 5:30, not 5:50, and that misreading has ruined real race plans. When converting between metric and imperial pace, the factor is the mile itself: multiply min/km by 1.609 to get min/mile. The speed converter handles the unit side whenever you would rather not.
A worked example: the 25-minute 5K
A 25:00 five-kilometer run:
- Pace: 25:00 / 5 = 5:00 per km
- In imperial: 5.0 × 1.609 = 8.05 min/mile = 8:03 per mile
- As speed: 60 / 5 = 12.0 km/h
And the reverse direction, the one race planning actually uses: to break 4 hours in a marathon (42.195 km), you need 240 / 42.195 = 5.69 min/km, which reads as 5:41 per km, held for the entire distance. Suddenly “sub-4” stops being a vibe and becomes a number you can train against and check at every split.
Predicting race times: the Riegel formula
You cannot just double your 5K time to predict your 10K, because nobody holds 5K pace for twice the distance. The standard correction is Peter Riegel’s formula:
T₂ = T₁ × (D₂ / D₁)1.06
The exponent 1.06 encodes how much humans slow as distance grows. Two worked predictions:
- From a 25:00 5K: 25 × (10 / 5)1.06 = about 52:07 for the 10K, not 50:00. The pace cost of doubling the distance is about 13 seconds per km.
- From a 1:45:00 half marathon: 105 × 21.06 = about 3:38:55 for the marathon, not 3:30.
Riegel assumes you are trained for the longer distance; a 5K runner who has never run past 8 km will not hit the marathon prediction by formula alone. Treat the output as the fair target for an equally prepared you, which is exactly the right number to build a training plan around.
Training paces: why slower builds faster
The most common training error is running everything at one proud, medium pace. Effective plans spread work across paces anchored to your current race pace, and a widely used anchoring (using our 5:00/km 5K runner):
| Run type | Rough anchor | For a 5:00/km 5K runner |
|---|---|---|
| Easy / recovery | race pace + 60 to 90 s per km | 6:00 to 6:30 /km |
| Long run | race pace + 45 to 90 s per km | 5:45 to 6:30 /km |
| Tempo (comfortably hard) | about 10K to half effort | about 5:10 to 5:25 /km |
| Intervals (5K effort and faster) | at or under race pace | 4:45 to 5:00 /km |
The counterintuitive part is the first row: most weekly mileage belongs there, a minute or more slower than race pace. Easy running builds the aerobic base that race pace is later built on, and running it too fast is the classic way to stay tired and stay the same speed. These anchors are heuristics, not lab values; runners chasing precision use threshold tests, but the table is the right starting grid.
Treadmill settings and pace
Treadmills speak speed, runners think pace, and the conversion is the same inversion as always: pace = 60 / speed.
| Treadmill | Pace |
|---|---|
| 10.0 km/h | 6:00 /km |
| 12.0 km/h | 5:00 /km |
| 6.0 mph | 10:00 /mile (about 6:13 /km) |
Two treadmill notes worth knowing: belt calibration drifts, so identical settings on two machines are not identical speeds, and a 1% incline is the common convention for approximating outdoor effort. Total session time at a given setting is plain multiplication, and for adding up interval sessions with rests, the hours calculator saves the clock arithmetic.
Pacing a race: the negative split
The fastest marathons in history were mostly run with a negative split: the second half slightly faster than the first. The physiology is unforgiving in one direction; minutes banked by going out fast are repaid with heavy interest after 30 km, while a controlled first half keeps the late kilometers honest. The practical recipe for a goal race: first quarter a few seconds per km slower than goal pace, middle half at goal pace, and spend whatever remains in the final quarter. The discipline costs almost nothing and routinely beats the brave start. For the energy side of endurance, fueling and body composition, the chain starts at the BMR and calories pillar.
Frequently asked questions
Why is my GPS pace jumping around mid-run?
Instant GPS pace is noisy by nature, especially near buildings and trees. Use lap pace or the average over the last kilometer for decisions, and trust the noise less the shorter the window.
Is min/km or min/mile the standard?
Neither is global: most of the world reads min/km, US and UK road running tradition reads min/mile. Know your race’s signage convention before the gun, because converting at kilometer 32 is nobody’s best math.
How accurate is the Riegel prediction?
Good across distances from 1,500 m to the marathon for trained runners, with the marathon as its weakest case because fueling and heat join the equation. Some runners use a slightly higher exponent for the marathon; the calculator output is the right planning anchor either way.
Should walkers use pace too?
Absolutely, the math is identical. Brisk walking sits around 9 to 12 min/km, and walk-run plans live entirely on pace arithmetic, which is what makes them so easy to follow.