At 21.1 kilometres, the half marathon is the fastest-growing race distance globally. It demands both aerobic endurance and pacing discipline. Use this calculator to find the exact per-km or per-mile pace needed for any target finish time, convert a recent performance into training zones, or predict your half marathon from a 10K result.
Preview
Ideal for runners targeting their first sub-2-hour half marathon, experienced runners building towards a marathon, coaches setting race-day pacing bands, and anyone converting a half marathon time into a training pace structure.
Pace is calculated by dividing your finish time by 21.0975 km (the official half marathon distance). Enter any two of pace, time, or distance and the calculator solves the third.
The Riegel race predictor formula (T2 = T1 × (D2/D1)^1.06) projects your half marathon time from shorter race performances. This is widely used by coaches and is accurate to within 2–3% for well-trained runners.
Training zones divide your race pace into five effort bands. The half marathon race pace itself typically corresponds to lactate threshold effort — the highest sustainable aerobic intensity.
Target: run under 2 hours
Inputs: Distance: 21.0975 km, Time: 1:59:59
Required pace: 5:41/km (9:09/mile). That is just under 5:41 per kilometre for the entire race.
Predict half marathon from a recent 10K
Inputs: 10K time: 50:00 (enter as distance 10km, time 50:00 on the main calculator)
Predicted half marathon: approximately 1:51:00–1:53:00 using the Riegel formula.
Find pace for a 1:45 half marathon
Inputs: Distance: 21.0975 km, Time: 1:45:00
Pace: 4:59/km (8:01/mile). This requires sub-5:00/km average for every kilometre.
You need to average 5:41/km (9:09/mile) for the entire 21.1km. That means every kilometre split on your watch should show approximately 5:41 or faster. Many runners aim to run km 1–5 at 5:45/km, hold 5:41/km through the middle, and push in the final 3km.
For recreational runners, finishing under 2:30 is a solid first-timer achievement. Sub-2:00 is a popular target for regular runners and represents a strong recreational performance. Sub-1:45 is competitive at most road races. Sub-1:30 is strong club-level for men and elite-recreational for women.
A common rule of thumb is to multiply your 10K time by 2.19. This calculator uses the Riegel formula for a more precise estimate. A 50-minute 10K runner can typically expect a half marathon around 1:50:00 to 1:55:00, depending on endurance training volume.
Start 10–15 seconds per kilometre slower than your target average pace. The adrenaline and fresh legs at the start make it easy to go out too fast, which leads to a dramatic slowdown after 15km. A controlled start almost always results in a faster finish time.
Most runners need to be running 35–50km per week consistently, including one long run of 16–18km, one tempo session (e.g. 6km at 5:30/km), and easy recovery miles. A structured 10–12 week plan targeting sub-2:00 typically produces best results.