How this instrument works
A half marathon covers a fixed 13.1094 miles (21.0975 km), and pace — time divided by distance — is the standard way runners plan and check effort across that distance. Because 13.1 miles is long enough for small pacing mistakes to compound badly by the final few miles, knowing an exact target pace per mile in advance, rather than guessing by feel, is central to most half marathon training plans.
This instrument divides the finish time you enter, in minutes, by the distance, in miles, defaulting to the standard 13.1-mile half marathon distance. A goal of 2:11:00, entered as 131 minutes over 13.1 miles, works out to an even 10:00 per mile — the kind of clean number many runners deliberately target because it's easy to check against a watch at every mile marker without doing mental arithmetic mid-race.
Coaches commonly recommend running the second half of a half marathon at least as fast as the first, ideally a touch faster — a pacing strategy called negative splitting. Having a precise target pace calculated ahead of time turns that strategy into something checkable in real time: comparing the actual mile-marker time against the target tells a runner within a mile or two whether they're on strategy or drifting off it.
- Enter Finish time (minutes) — your actual or goal half marathon time; 131 is shown as a 2:11:00 reference point.
- Enter Distance (miles) — defaults to 13.1 for the standard half marathon distance; adjust only if your course measured differently.
- Read Pace (min per mile) — the average pace across the full distance, useful for checking progress at each mile marker.
- Multiply the pace by any mile marker number to get a target clock time at that point in the race.
- Distance must be greater than zero — the instrument will prompt you if it is left at zero or blank.
Worked example — a 5-mile tempo run at goal effort
Enter 30 into Finish time (minutes) and 5 into Distance (miles) — a 5-mile tempo or progression run, the kind many half marathon training plans include mid-week to sharpen top-end pace ahead of race day. Pace reads 6.00, meaning 6 minutes per mile.
That 6:00/mile effort runs well inside actual half marathon race pace for most runners — it's a training-session intensity, not a full 13.1-mile pace. For comparison, a runner targeting an even 10:00/mile average, entered as 131 minutes over the full 13.1-mile distance, would cross the finish line in 2:11:00; the same time ÷ distance formula produces both figures, just at very different distances and efforts.
Questions
What's a good half marathon pace for a first-timer?
Many first-time half marathoners finish somewhere between 9:30 and 12:00 per mile, working out to roughly 2:05 to 2:37 for the full 13.1 miles, though this varies enormously with running background. Enter your own goal finish time into this instrument to get a precise per-mile target to check against rather than relying on a general range.
How is this different from the 5k-pace instrument on this site?
Both use the identical time ÷ distance formula, but the effort and pacing strategy behind each differ sharply — 5K pace is raced close to lactate-threshold or VO2-max intensity over roughly 15-30 minutes, while half marathon pace is held aerobically for two hours or more. A runner's 5K pace is typically noticeably faster, per mile, than their half marathon pace.
What is a negative split, and how does this calculator help with it?
A negative split means running the second half of a race faster than the first — a pacing strategy many coaches recommend for the half marathon specifically, since starting conservatively leaves more in reserve for the closing miles. Once you have a target pace from this instrument, comparing your actual mile-marker times against it during the race tells you in real time whether you're holding, ahead of, or falling behind that strategy.
Why does the half marathon measure 13.1 miles rather than a round number?
The half marathon's official distance is exactly half of a full marathon, which itself is fixed at 26.2 miles (42.195 km) — so a half marathon comes to precisely 13.1094 miles, or 21.0975 km, rounded in everyday use to '13.1'. That precise figure is set by World Athletics, the sport's global governing body, and is identical at every certified half marathon course worldwide.
Can I use this for a training run instead of the full half marathon distance?
Yes — enter the actual time and distance of any run, such as a mid-week tempo session, and the instrument returns that run's pace using the same formula. Comparing a shorter training-run pace against your half marathon goal pace is a common way to judge whether a session was run too hard, too easy, or right where race pace needs to be.