Running Pace Calculator

VDOT is Jack Daniels' fitness number — a single score that captures your current aerobic capacity. Higher = faster. It's calculated from any recent race result (5K, 10K, half, marathon all work). Once you have your VDOT, the calculator gives equivalent paces at all 5 training zones (easy / marathon / threshold / interval / repetition) — the foundation of Daniels-style training.

Riegel's formula (1981): T₂ = T₁ × (D₂/D₁)^1.06. The exponent 1.06 means pace slows slightly as distance increases — you can't run a marathon at your 5K pace. The predictor works best for distances within 4× of your input (e.g. a 5K result predicts your 10K, half, and marathon reasonably well; a 1-mile result is less reliable for marathon).

Subjective, but reference points: casual jog ~7:00/km, fit recreational runner 5:00-6:00/km, sub-elite ~4:00/km, elite marathon runners ~3:00/km. World records: marathon ~2:53/km, 5k ~2:30/km. Most people improve from the 7:00 range to the 5:00 range in a year of consistent training.

Different paces train different physiological systems. Easy pace builds aerobic base. Marathon pace is goal race pace. Threshold pace (tempo) raises lactate threshold. Interval pace develops VO2max. Repetition pace improves running economy and speed. A balanced training week mixes 70-80% easy, 10-15% threshold/marathon, 5-10% interval/repetition.

Half = 21.0975 km. Full = 42.195 km. They're not round numbers because the marathon distance was standardised in 1908 to match the King's preferred course length (from Windsor Castle to White City stadium). Half is exactly half of that.