Running Pace Calculator

Running Pace Guide

Pace vs Speed

Pace and speed describe the same physical reality from opposite ends of the relationship, and runners and physicists tend to use different conventions. Pace (typically minutes per kilometre or minutes per mile) is how runners think about effort — it answers 'how long does it take me to cover one km?' Lower pace numbers mean faster running. Speed (km/h or mph) is the physics-style measure — distance covered per unit time, where higher numbers mean faster. They're inversely related: 5:00/km = 12 km/h (because at 5 minutes per km you cover 12 km in an hour); 6:00/km = 10 km/h; 4:00/km = 15 km/h. The conversion: km/h = 60 ÷ (minutes per km), and min/km = 60 ÷ (km/h). For miles: 5:00/mile ≈ 12 mph; 8:00/mile = 7.5 mph; 10:00/mile = 6 mph. Why do runners use pace rather than speed? Because at the speeds humans run, pace gives clean round numbers that scale nicely (5:00/km is a benchmark; 12 km/h is an awkward speed to think about during a run). Treadmill conversions: 10 km/h on the display = 6:00/km pace; 12 km/h = 5:00/km; 14 km/h = 4:17/km; 16 km/h = 3:45/km. The general 'pace = 60 ÷ km/h' formula lets you decode any treadmill speed into running pace. This calculator handles both directions and converts between km and miles.

Race Time Predictions

Predicting your race time at a new distance from a known race time at another distance uses the Riegel formula: T2 = T1 × (D2/D1)^1.06, where T1 and T2 are the times and D1 and D2 the distances. The 1.06 exponent (rather than a simple 1) reflects the fact that longer races are proportionally slower — you simply can't sustain 5 km pace for a marathon, however well trained. The formula encapsulates this physiological reality from empirical data across many runners. A worked example: if you've run a 5 km in 25 minutes (5:00/km pace), the Riegel formula predicts your 10 km time at 25 × (10/5)^1.06 ≈ 25 × 2.085 ≈ 52 min (5:12/km — slightly slower than 5km pace). For a half marathon (21.1 km): 25 × (21.1/5)^1.06 ≈ 25 × 4.65 ≈ 116 min, about 1:56 (5:30/km). For a marathon: 25 × (42.2/5)^1.06 ≈ 25 × 9.7 ≈ 242 min, about 4:02 (5:44/km). The formula is most accurate when both your training and your race distance match — a sprinter's Riegel prediction for the marathon would be optimistic because they lack endurance training; an ultrarunner's 5 km prediction from a marathon time may be conservative. As a rule, predictions are most reliable when comparing distances within the same general range (5 km to half marathon works well; 1 km to marathon stretches the formula). This calculator applies Riegel and gives predictions for common race distances from any one input.

Training Paces by Zone

Training at the right paces — not all of them being 'race pace' — is the foundation of running improvement, and most amateur runners spend too much time at moderately-hard paces that don't optimally develop fitness. The common framework distinguishes several zones: easy/recovery runs should be 60–90 seconds per km slower than 10 km race pace — easy enough to hold a conversation, designed to build aerobic base and aid recovery; this should make up the majority (often 70–80%) of weekly mileage. Long runs are typically 45–75 seconds slower than 10 km pace, building endurance over time. Tempo or threshold runs are roughly at 10 km–half marathon race pace — 'comfortably hard', sustainable for 20–40 minutes, building lactate clearance. Intervals at VO2max pace are run at slightly faster than 5 km race pace, in short reps with recovery between (e.g. 6 × 800 m), building maximum aerobic capacity. Speed/repetition work is faster still, used sparingly. The polarised training model — lots of easy running plus a small amount of hard work, very little 'moderate' — has strong evidence behind it for endurance development. The most common mistake is running easy runs too hard, which prevents both recovery and the high-quality hard sessions that drive improvement. A pace calculator helps you set targets for each zone from a single race time, ensuring easy runs really are easy and hard runs are properly hard.

Converting Between Treadmill Speed and Pace

UK treadmills show km/h; US treadmills show mph. To convert km/h to min/km: divide 60 by the speed. So 10 km/h = 6:00/km, 12 km/h = 5:00/km, 15 km/h = 4:00/km. 1 mph = 1.609 km/h. A 6 mph treadmill setting = 9.66 km/h = 6:13/km pace.