Enter your 10K time and see your race pace per km and per mile, a predicted half-marathon time, and your VDOT training zones.
Your 10K base is your half-marathon foundation
Most runners are 10–14 weeks from their first half marathon.
The training zones are identical — you just need to extend the long run. PaceForm builds a plan calibrated to your goal time and schedule.
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Race pace per km and mile, plus predicted half-marathon finish time via Riegel formula.
Your 10K time is converted to an equivalent half-marathon time using the Riegel formula (T₂ = T₁ × (D₂/D₁)^1.06, exponent 1.06). From there, Jack Daniels' VDOT methodology derives your training zones: easy at 1.13–1.25× HM pace, tempo at ~0.91×, speed intervals at ~0.85×, and long run at ~1.20×. These ratios reflect the physiological stimulus each intensity targets — not arbitrary percentages.
It shows your race pace per kilometre and per mile for your 10K goal time, a predicted half-marathon time using the Riegel formula, and four VDOT training zones: easy (aerobic base), tempo (lactate threshold), speed (VO₂max intervals), and long run. These are the same paces used by coaches following Jack Daniels' methodology.
The Riegel formula (T₂ = T₁ × (D₂/D₁)^1.06) is accurate to within 3–5% for most runners when both distances are raced at equivalent effort. The prediction is most accurate when your 10K was raced recently and your training has included long runs of 16+ km. Runners with limited long-run training often find the prediction optimistic by 3–6 minutes.
Using the Riegel formula, a 10K time of approximately 54:30 predicts a half-marathon finish of 1:59:59. In practice, most runners targeting sub-2 hours have 10K times in the 52:00–56:00 range. If your 10K is around 58:00, sub-2:00 may require an additional training cycle to build the required aerobic base.
The training zones overlap almost entirely — easy, tempo, and speed sessions are the same. The main difference is volume: half marathon training requires more total mileage (especially the long run, which builds to 18–21 km vs 14–16 km for 10K). Runners who've built a 10K base are well-positioned for a half marathon in 10–14 additional weeks.
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