Half Marathon Pace Calculator

The official IAAF half-marathon distance is 21.0975 kilometers, which is exactly half of the full marathon's 42.195 km. Converted using the international mile (1 mile = 1.609344 km exactly), that comes out to 13.10937779 miles, which the calculator rounds to 13.10938 mi. The common shorthand 13.1 mi is the same number truncated to one decimal: it is short by 36 feet (about 11 meters) over the full race. For pace and split planning the difference is trivial (under 5 seconds at 8:00/mi pace), but the calculator uses the full 13.10938 figure so the final cumulative split time on the table matches your target finish to the second.

Sub-1:30 half: 6:52/mile or 4:16/km, average speed 8.74 mph. Sub-1:45 half: 8:00/mile or 4:58/km, 7.49 mph. Sub-2:00 half: 9:09/mile or 5:41/km, 6.55 mph. Sub-2:15 half: 10:18/mile or 6:24/km, 5.83 mph. Sub-2:30 half: 11:27/mile or 7:06/km, 5.24 mph. For context, the global median half-marathon finish has hovered around 1:58 for men and 2:11 for women in recent years (Running USA, RunRepeat), so a sub-2:00 puts you near or above the median. Use the splits-per-mile table to confirm what each mile marker on your watch should read at the target pace, and the splits-per-km table to cross-check at metric race signage.

The calculator uses five widely cited recreational bands. Elite is under 1:30:00 (top single-digit percent of fields). Competitive is 1:30:00 to 1:44:59 (strong age-group runners). Good is 1:45:00 to 1:59:59 (a well-trained hobby runner). Average is 2:00:00 to 2:30:00 (typical first-half-marathon territory; the global median sits inside this band). Recreational is anything over 2:30:00 (often run-walk pace, ideal for first-timers and walkers). These are heuristics, not absolute standards: a 2:00 finish in a flat road race differs from a 2:00 finish on a hilly trail event, and age-graded performance tables (USATF Masters, WMA) are the right tool when you want apples-to-apples comparisons across age groups.

No. The Boston Marathon's qualifying standards (BQ) require a certified finish at the full 42.195 km marathon distance. Half-marathon times are never accepted as direct qualifiers, no matter how fast. What the calculator does instead is predict your equivalent marathon time using Pete Riegel's race-time formula scaled to the half-to-full ratio (marathon time approximately equals half-marathon time multiplied by 2.105), then compare that prediction against the classical open standards (sub-3:00 male, sub-3:30 female). A 1:25 half predicts a 2:59 marathon and the calculator notes that as projected to beat the open male BQ standard; the actual qualification still requires you to run, and beat, the published BAA age-group standard at a sanctioned full marathon.

Within about 5 to 10 percent for runners who have trained specifically for the marathon distance, and noticeably optimistic for runners who have only trained for the half. The formula comes from Pete Riegel's 1981 paper (Athletics, May 1981), which fit Tn = T1 * (Dn/D1)^1.06 to large datasets of distance-running performances. Substituting D2/D1 = 2 gives 2^1.06 = 2.0853, which the coaching community has rounded to 2.105 as a more conservative real-world figure that better matches finish-time data from large marathons. Riegel himself warned the formula degrades past about a 3x distance jump and assumes equivalent training. In practice, expect a Riegel marathon prediction from a half-marathon time to undershoot by 5 to 20 minutes if your long runs top out at 10 miles, and to be reasonably close if your weekly volume and long-run length are tuned for the full distance.