How it works
required pace = goal time ÷ 13.1094 mi (or ÷ 21.0975 km)
Average pace is elapsed time divided by distance — the kinematic definition of speed expressed as time per unit. For a half marathon the distance is fixed at exactly 21,097.5 m (13 miles 192.5 yards, World Athletics standard), so the only variable is your goal time. We compute everything in SI units (metres and seconds) internally and convert to miles or kilometres only at the display edge, so both unit views are always consistent (ADR-9). The first 10K split assumes perfectly even pacing — a useful checkpoint since 10 km marks appear on most major half-marathon courses. The half rewards even effort: it is long enough that an over-fast start bleeds into the closing miles, but short enough that most trained runners can hold one pace start to finish, so the 10K split is the honest mid-race read on whether you set off too quick.
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 do I need to run a sub-2 hour half marathon?
To finish a half marathon in under 2:00:00 you must average faster than 9:09 per mile (5:41 per km). That requires passing the 10K mark in under 56:50 on even pace.
What pace do I need for a sub-1:45 half marathon?
A 1:45:00 half marathon requires holding 8:01 per mile (4:59 per km). At even pace your first 10K split is around 49:44. Most runners target 49–50 minutes at the 10K mark and negative-split the rest.
What pace do I need for a sub-1:30 half marathon?
Under 1:30 means averaging faster than 6:52 per mile (4:16 per km) — a first 10K split of under 42:39. This is a competitive target requiring solid base mileage and tempo-run training.
Is even pace realistic for a half marathon?
Even pace is the mathematical ideal and the simplest target. Many half-marathon runners can execute near-even splits because the distance is short enough to avoid severe glycogen depletion. A slight negative split — running the second half 15–30 seconds faster — is also common and helps manage early-race adrenaline.
Should I pace a half marathon by mile or by kilometre?
Use whichever your course marks — and this is where the unit gap bites over 13.1 miles. A sub-2:00 half is 9:09 per mile but 5:41 per km, and at that effort a few seconds of drift per kilometre compounds into a minute lost by the finish. The calculator shows both figures plus the 10K split so a kilometre-marked course and a mile-based watch stay in agreement the whole way.
Why is the first 10K split shown?
10 km markers appear on nearly every major half-marathon course and many runners use a 10K watch split to confirm they are on pace. At even pace your first 10K represents 47.4 % of the total distance, so a slightly conservative first 10K sets up a strong finish.
How do I use the per-400 m time to train for a half?
A standard track lap is 400 m, so the per-400 m figure is your goal lap time at half-marathon effort. Half-marathon prep leans on long tempo blocks rather than short reps, so use it for sustained track sets — repeats of 2–3 km at this lap time — to groove the even, controlled pace the distance demands before you confirm it at the 10K checkpoint on race day.
Pace figures are mathematically exact for the goal time you enter. The first 10K split assumes perfectly even pace and is not a personalised prediction. General information for planning purposes only — not medical, coaching, or race-strategy advice.