Health & Medicine · Fitness · Cardio & Endurance
Half Marathon Pace Calculator
Calculate your required pace, finish time, or total speed for a half marathon (21.0975 km / 13.1094 mi) from any two known values.
Calculator
Formula
Pace is total finish time (in minutes) divided by distance. Finish Time is pace (min/unit) multiplied by distance. Speed is distance divided by total time in hours. D = 21.0975 km or 13.1094 mi for a half marathon.
Source: World Athletics (formerly IAAF) — official half marathon distance 21.0975 km / 13.1094 mi.
How it works
A half marathon is exactly 21.0975 kilometres (13.1094 miles) under World Athletics rules. The core relationship is straightforward: Pace = Total Time ÷ Distance. If your target finish time is 1 hour 45 minutes (105 minutes) and you are running in km, your required pace is 105 ÷ 21.0975 ≈ 4.976 min/km, which converts to 4 minutes and 59 seconds per kilometre.
Average speed follows the inverse: Speed = Distance ÷ Time (in hours). For the same 1:45:00 finish, speed = 21.0975 ÷ 1.75 ≈ 12.06 km/h. These two outputs — pace and speed — describe the same effort from different angles: pace is preferred by most road runners while speed is common on treadmills and in cycling-influenced training platforms.
This calculator is useful for race-day planning, treadmill settings, interval design, and comparing performances across different conditions. Coaches also use pace targets to set tempo workout zones and threshold sessions aligned with an athlete's goal race time.
Worked example
Goal: Finish a half marathon in 1 hour 52 minutes 30 seconds (6750 seconds total).
Step 1 — Convert to decimal minutes: 1×60 + 52 + 30/60 = 112.5 minutes.
Step 2 — Calculate pace per km: 112.5 ÷ 21.0975 = 5.332 min/km → 5 minutes 20 seconds per kilometre.
Step 3 — Calculate pace per mile: 112.5 ÷ 13.1094 = 8.582 min/mi → 8 minutes 35 seconds per mile.
Step 4 — Calculate average speed: 21.0975 ÷ 1.875 hours = 11.25 km/h (6.99 mph).
Interpretation: To hit 1:52:30 you need to hold 5:20/km (8:35/mi). A useful rule of thumb — if you feel comfortable at that pace after 16 km, you can afford to negative-split the final 5 km.
Limitations & notes
This calculator assumes a perfectly constant pace throughout the race — in practice, most runners go out slightly faster and slow in the final kilometres due to fatigue, hills, and weather. GPS watches and race timing mats record actual splits, which will always deviate from this theoretical even-pace model. The official half marathon distance (21.0975 km) is measured along the shortest possible legal running line (the tangent path); your watch may record 21.2–21.5 km due to natural weaving. Use the official distance for pace planning, not your GPS distance. For treadmill use, note that most machines display speed in km/h or mph and require you to convert — this calculator provides both. Finally, pace targets derived here do not account for altitude, heat, or relative humidity, all of which can meaningfully slow performance.
Frequently asked questions
What is the official distance of a half marathon?
The official half marathon distance is 21.0975 kilometres (13.1094 miles) as defined by World Athletics. This is exactly half of the full marathon distance of 42.195 km. Race courses are certified to this distance measured along the shortest legal running path.
What pace do I need to run a sub-2-hour half marathon?
To finish a half marathon in under 2:00:00 (120 minutes) you need to average faster than 120 ÷ 21.0975 ≈ 5.688 min/km — that is 5 minutes 41 seconds per kilometre or approximately 9 minutes 9 seconds per mile. Aim for 5:39/km (9:06/mi) to give yourself a small buffer.
How do I convert my pace from min/km to min/mile?
Multiply your min/km pace by 1.60934 (the number of kilometres in a mile). For example, 5:00/km × 1.60934 ≈ 8:03/mi. Alternatively, divide your min/mile pace by 1.60934 to get min/km. This calculator does the conversion automatically based on the unit you select.
What is a good half marathon time for a beginner?
For a first-time half marathoner, finishing anywhere between 2:00 and 2:30 is very respectable. That equates to a pace of roughly 5:41–7:06 min/km (9:09–11:27 min/mi). Most training plans for beginners target a 2:15–2:30 finish. Elite men race around 58–60 minutes; elite women around 65–67 minutes.
Should I run even splits or negative splits in a half marathon?
Research and elite race data consistently support negative splitting — running the second half slightly faster than the first. Starting 5–10 seconds per km slower than your goal pace for the first 7 km conserves glycogen and reduces the risk of hitting the wall. Most world records and personal bests at the half marathon distance have been set with negative or even splits. Use this calculator to plan your first-half pace (slightly slower) and second-half pace (slightly faster) around your target finish time.
How accurate is GPS pace data during a half marathon?
Consumer GPS watches typically have a horizontal accuracy of ±3–5 metres, which accumulates over 21 km. Most runners record 21.2–21.5 km on their watch due to natural weaving and GPS drift, meaning displayed pace will appear slightly slower than actual effort. For race planning, always use the certified course distance of 21.0975 km, not your watch's recorded distance.
Last updated: 2025-01-30 · Formula verified against primary sources.