The 5K is the benchmark distance for every runner. It is short enough that most people can finish one after a few weeks of training, yet long enough that your time reveals real endurance. This 5K pace calculator takes your finish time and breaks it into the two numbers runners care about most: your pace per kilometer and your pace per mile. It then projects what that same fitness level would produce over a 10K, a half-marathon, and a full marathon using the classic Riegel race-time prediction formula.
Type in your hours, minutes, and seconds and every result updates instantly. Whether you are chasing a personal best on the track or estimating how long your first half-marathon will take, the numbers below give you a concrete target to train toward.
How to Use
- Enter the 5K Hours portion. Most runners set this to 0, since nearly every 5K finish is under an hour; hikers and walkers may need 1.
- Enter the 5K Minutes portion. If you finished in 25 minutes flat, type 25 here.
- Enter the 5K Seconds portion (0 to 59). A 25:32 finish means 32 seconds here.
- Read the result card: your Pace (min/km) and Pace (min/mile) show how fast you ran each unit of distance.
- Scroll to the predicted races. The calculator applies the Riegel exponent of 1.06 to estimate your likely 10K, half-marathon, and marathon times if you keep training.
The highlighted Pace (min/km) is your single most useful figure. It is the number you should target on training runs: if your 5K pace is 5:00 per km, steady training runs around 5:30 to 6:00 per km build the aerobic base that lets you race faster.
The Riegel Prediction Formula
Your pace is the easy part. If you ran 5 kilometers in 25 minutes, your pace is simply 25 divided by 5, which equals 5:00 per kilometer. Converting to miles is a multiplication by 1.609344, since one mile equals 1.609344 kilometers.
The race predictions use the Riegel formula, published by Peter Riegel in "Athletic Records and Human Endurance" (1981):
T2 = T1 × (D2 / D1)^1.06
Where T1 is your known time over distance D1, and T2 is the predicted time over distance D2. The 1.06 exponent captures the fact that runners slow down slightly as races get longer: doubling the distance does not quite double the time.
Worked example: a 25:00 5K (1500 seconds) predicts a half-marathon of 1500 × (21.0975 / 5)^1.06, which equals about 1:55:00. The same fitness predicts a 10K near 52:07 and a full marathon near 3:59:47. These are estimates based on even pacing and proper training; hills, heat, wind, and a late-race wall will shift the real result by a few percent.
Reading Your Pace
Pace bands help you place your result in context:
- Elite and near-elite — under 18:00 for men, under 21:00 for women. This is 3:36 per km or faster and requires years of structured training.
- Competitive age-group — 18:00 to 22:00. You run intervals, tempo sessions, and long runs consistently.
- Fitness runner — 22:00 to 30:00. You train several times a week and race for fun and fitness.
- Beginner or jog-walk — 30:00 to 45:00. You have built up from the couch and are still adding endurance.
Keep in mind that pace slows with fatigue. The Riegel predictions assume you hold roughly the same relative effort; in practice, most runners land within about 5% of the predicted time when the course is flat and the weather is cool.
Examples
Example 1 — A 25:00 recreational runner. You finish a local 5K in 25 minutes flat. Your pace is 5:00 per km (about 8:02 per mile). The calculator predicts a 10K around 52:07, a half-marathon near 1:55:00, and a marathon near 3:59:47. If your goal is a sub-2:00 half, this 5K shows you are right on the edge and need to sharpen your speed work by about 2 to 3 percent.
Example 2 — An 18:00 competitor. A strong runner crosses the line in 18 minutes. That is 3:36 per km (about 5:47 per mile). The projected 10K is 37:32, the half-marathon 1:22:48, and the marathon 2:52:38. To break 2:50 in the marathon, you would need to either shave the 5K down toward 17:40 or commit to a block of long runs so your marathon-specific endurance exceeds what pure 5K speed suggests.
Example 3 — A 36:30 beginner. Someone new to running completes their first 5K in 36 minutes 30 seconds. Their pace is 7:18 per km (about 11:44 per mile). The predicted half-marathon is roughly 2:47:54 and the marathon 5:50:05. These are optimistic long-term targets; a beginner should focus on finishing shorter races first, since marathon predictions this far out are unreliable until the runner can hold the pace comfortably over 15K or more.
FAQ
What is a good 5K time?
For men, a good 5K is often considered under 25 minutes; for women, under 28 minutes. Competitive age-group runners finish in the high teens, while beginners are typically between 30 and 40 minutes. Use your pace per km as the honest measure, since it is what you will actually train against.
How do I convert 5K pace to minutes per mile?
Multiply your minutes-per-kilometer pace by 1.609344. For example, 5:00 per km is 5 × 1.609344 = about 8:02 per mile. This calculator shows both figures automatically so you do not have to do the conversion by hand.
What pace should I run to hit a 25-minute 5K?
To finish a 5K in 25 minutes, you need to average 5:00 per kilometer, or about 8:02 per mile, for the entire race. Practically, that means running each of the five kilometers at roughly the same speed rather than sprinting the first and walking the last.
How accurate are the 10K, half, and marathon predictions?
The Riegel formula is a well-established estimate and most trained runners land within about 5 percent of their predicted time. It is less accurate for absolute beginners, for very hilly or warm courses, and for anyone whose training has not yet prepared them for the longer distance. Treat the predictions as planning targets, not guarantees.
Why does a 25-minute 5K predict a 1:55 half-marathon rather than 1:45?
Because of the 1.06 exponent. Doubling the distance from 5K to the half-marathon does not double the time; runners slow down as fatigue builds. The formula accounts for that gradual slowdown, so a 25-minute 5K projects to about 1:55 over 21.1 km, not a simple linear 1:45.
Can I use this pace to set a marathon goal?
Yes, but cautiously. A marathon prediction from a single 5K is a rough starting point. It assumes you have done the long-run work. Use it to choose a training block, then re-predict after you have completed a long run at goal pace, when the estimate becomes much more trustworthy.
Is this calculator different from a marathon pace calculator?
Yes. A marathon pace calculator starts from a marathon finish time and works backward to a per-mile pace. This 5K calculator starts from a short 5K result and projects forward to longer distances, while also giving you your raw min/km and min/mile pace.
Disclaimer
This 5K pace calculator is provided for informational purposes only. It is a planning and estimation tool and does not constitute medical, training, or coaching advice. Predicted times come from the Riegel formula and your entered inputs; real results vary with hills, weather, fatigue, footwear, race-day conditions, and fitness. If you have any health concerns, injuries, or are beginning a new exercise program, consult a qualified doctor or coach before adjusting your training.