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One Rep Max (1RM) Calculator
Estimate your one-rep max (1RM) from a set of reps using the Epley, Brzycki and Lombardi formulas, with a percentage chart.
Pace Calculator
Calculate running pace, finish time or distance, with per-km and per-mile pace, speed and race-time predictions.
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How to use this calculator
Enter your values after choosing the type of calculation in the tabs. The result updates as you type; press Calculate to confirm and jump to the result on mobile. Use Share to send the calculator with your result.
Pace formulas
pace = time ÷ distance
time = pace × distance
distance = time ÷ pace
speed (km/h) = 60 ÷ pace (min/km)
Example: 5 km in 25:00 is 25 ÷ 5 = 5:00 per km, or 8:03 per mile (12 km/h).
Race-time prediction
Predictions use Peter Riegel’s endurance formula (1977), popular with runners and coaches:
T₂ = T₁ × (D₂ ÷ D₁)^1.06
A 25:00 5K predicts about 52:07 for 10K and about 4:00 for the marathon if you train properly for the longer distance.
Common race distances
| Race | Kilometers | Miles |
|---|---|---|
| 5K | 5 | 3.11 |
| 10K | 10 | 6.21 |
| Half marathon | 21.0975 | 13.11 |
| Marathon | 42.195 | 26.22 |
Frequently asked questions
What is a good 5K pace?
It depends on age and training; many recreational runners finish between 25 and 35 minutes (5:00–7:00 per km).
How do I convert pace per km to pace per mile?
Multiply by 1.609344. 5:00/km × 1.609 = 8:03/mile.
How accurate is the Riegel formula?
It works well between similar distances; marathon predictions from a 5K are often optimistic.
About this tool
- Written by
- [Author: to be assigned]
- Reviewed by
- Expert review pending
- Last updated
- 31 Oct 2026
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