Pace Calculator
Training for a 10K, half marathon, or marathon and want to nail the pace you’ll need to hit your goal? This tool does the math for you: enter a distance and a time to instantly get your pace (min/km), speed (km/h), and projected finish times for the standard race distances.
How to use the calculator
Choose your distance (5K, 10K, half marathon, marathon, or a custom distance).
Enter your time in hours, minutes and seconds, either a recent race result or your target time.
Check your results: pace, speed, and the prediction table that projects your performance across other distances.
Two practical uses: double-check your target pace for race day (e.g. “what pace do I need to run to finish my marathon in 3:30?”), or estimate your potential at a distance you’ve never raced based on a recent time.
Pace vs. speed: what’s the difference?
Your pace is the time it takes to cover one kilometer (min/km), the go-to metric for road runners. Your speed is the distance covered in one hour (km/h). It’s the same information, just expressed differently:
5:00 min/km = 12 km/h
4:30 min/km = 13.3 km/h
4:00 min/km = 15 km/h
The calculator converts one to the other automatically.
How the time predictions are calculated
The projection table uses the Riegel formula, a staple in running:
T2 = T1 × (D2 / D1)^1.06
In plain terms, your predicted time over a new distance depends on your known time and the ratio between the two distances, with a 1.06 factor that reflects the drop in pace as the distance increases. That’s why you’ll never run a marathon in exactly double your half-marathon time: endurance matters.
Example: a runner who clocks 45:00 for 10K gets a projection of around 1:39 for the half marathon and 3:27 for the marathon, assuming the endurance training is there to back it up.
Limits you should know about
These predictions assume training that matches the target distance and a comparable course. A marathon projected from a 5K will be optimistic if you haven’t built the endurance. Elevation gain, heat, wind and pacing strategy will all move the real finish time. Treat these numbers as a working target, not a guarantee.
FAQ
How do you convert pace to km/h? Divide 60 by your pace expressed in decimal minutes. A 5:00 min/km pace (5.0) gives 60 / 5 = 12 km/h. The calculator does it automatically.
What pace do you need for a 4-hour marathon? About 5:41 min/km (10.5 km/h) over 42.195 km. Select “Marathon” and enter “4:00” in the tool to confirm.
Does the calculator work for the half marathon? Yes. Select “Half marathon” (21.0975 km) and enter your time to get pace, speed and projections.
Are the predictions reliable? They’re reliable for nearby distances and consistent training. The bigger the gap between your reference distance and the projected one, the larger the error margin.