How it works
required pace = goal time ÷ 13.1094 mi (or ÷ 21.0975 km)
The half marathon measures 21,097.5 m — 13 miles plus 192.5 yards under World Athletics rules — so once you set a goal time, the required pace is fully determined: time divided by distance. Internally the tool works in meters and seconds and converts to miles or kilometers only when displaying, keeping both unit views in lockstep. The 10K checkpoint assumes dead-even pacing, which suits this race: it is long enough to punish a hot start yet short enough that trained runners can genuinely hold one pace throughout, so the 10 km marker gives the most honest early verdict on your plan.
Sources
- Half-marathon distance — World Athletics standard World Athletics (formerly IAAF) — the half marathon is defined as exactly 21.0975 km (13 miles 192.5 yards).
- Definition of pace (average speed) Average speed = distance ÷ time (kinematics); pace is its inverse, expressed as time per unit distance. Halliday, Resnick & Krane, "Physics", 4th ed., §2-2.
- Even-pace strategy in distance running Riegel, P. S. (1981). "Athletic Records and Human Endurance." American Scientist 69(3), 285–290. Even-pace or slight negative-split strategies minimise energy cost over long events.
FAQ
What pace breaks 2 hours in the half marathon?
A sub-2:00:00 finish demands averaging quicker than 9:09 per mile (5:41 per km), which on even pacing means reaching 10K in under 56:50. Do this checkpoint math before race morning, not during mile nine.
What does a 1:45 half marathon take?
A 1:45:00 finish requires 8:01 per mile, or 4:59 per kilometer, with an even-pace 10K split of about 49:44. Plenty of runners aim to reach 10K in 49–50 minutes and then press gently over the closing miles rather than banking time early.
And a sub-1:30 half?
Breaking 1:30 means holding under 6:52 per mile (4:16 per km) and clearing 10K by 42:39 on level pacing — firmly competitive territory that usually rests on consistent mileage and regular tempo work.
Does this work in miles and kilometers?
Yes, and over 13.1 miles the distinction earns its keep: many courses mark kilometers while most American watches default to miles. The tool shows the same goal as both pace figures, so your watch and the course markings never argue with each other.
Is perfectly even pacing realistic over 13.1 miles?
It is the mathematical ideal and, for the half, a reachable one — glycogen depletion rarely forces the fade it can in a full marathon. Still, hills, heat, crowded early miles, and adrenaline bend real splits, and a mild negative split (second half 15–30 seconds quicker) is a well-tested alternative.
Can beginners use it?
Yes — pick a modest goal time and the calculator hands you the pace and the 10K checkpoint that keep an ambitious start in check. First-timers gain the most from the even-split framing, since going out too fast is the classic rookie mistake at this distance.
Can competitive runners use it too?
The per-400 m lap figure is the racing-focused feature: it converts goal pace into a track lap time, ready for sustained sets such as 2–3 km repeats at target rhythm. And since the first 10K covers 47.4% of the race, that split doubles as a precise mid-race audit.
The pace, lap, and 10K figures are exact arithmetic for whatever goal time you enter — they say nothing about whether that goal fits your current fitness. Use them for planning and pacing rehearsal; bring training-load and health questions to a coach or physician.