What is the Half Marathon Pace Calculator?
A half marathon covers exactly 21.0975 kilometers (13.1094 miles). This calculator converts your target or actual finish time into an average running pace — expressed as minutes and seconds per kilometer and per mile — plus your average speed. It is useful for planning race-day effort, setting training targets, and comparing performances across distances.
How to use it
Enter your finish time in hours, minutes and seconds. The calculator divides the total time by the half marathon distance to give your average pace. For example, a 1:45:00 finish means you ran each kilometer in roughly the same average time throughout the race.
The formula explained
First the time is converted to seconds: \(\text{Total seconds} = \text{hours} \times 3600 + \text{minutes} \times 60 + \text{seconds}\). Pace per kilometer is then \(\text{Total seconds} \div 21.0975\), and pace per mile is \(\text{Total seconds} \div 13.1094\). Speed is the distance divided by the time in hours.
$$\text{Pace}_{\text{km}} = \frac{T}{21.0975} \quad\text{(s/km)}$$$$\text{where}\quad T = \text{Hours} \times 3600 + \text{Minutes} \times 60 + \text{Seconds}$$$$\text{Pace}_{\text{mile}} = \frac{T}{13.1094} \quad\text{(s/mi)}$$$$\text{Speed} = \frac{21.0975}{T / 3600} \quad\text{(km/h)}$$
Worked example
Suppose you finish in 1 hour 45 minutes (6300 seconds). Pace per km = \(6300 \div 21.0975 \approx 298.61\) s/km \(\approx\) 4:59 min/km. Pace per mile = \(6300 \div 13.1094 \approx 480.57\) s/mi \(\approx\) 8:01 min/mi. Average speed \(\approx 21.0975 \div 1.75\,\text{h} \approx 12.06\) km/h.
FAQ
Is a half marathon 13.1 miles exactly? It is 13.1094 miles, equal to 21.0975 km. We use the full precision so your pace is accurate.
What is a good half marathon pace? Recreational runners often target 5:00–6:30 min/km; a sub-2-hour half marathon needs about 5:41 min/km.
Does this account for hills or splits? No — it gives a single even average pace. Real races vary with terrain, fatigue and pacing strategy.
