Guide · Updated November 2026 · How we check our numbers

Running Pace, Race Predictions and Heart Rate Zones

Three numbers help most runners train smarter: pace, predicted race times and heart rate zones.

Pace

Pace = time ÷ distance. A 5 km run in 25:00 is 5:00 per km, or about 8:03 per mile (1 mile = 1.609344 km).

Predicting race times

The Riegel formula scales a recent result: T₂ = T₁ × (D₂ ÷ D₁)^1.06. From a 25:00 5K it predicts about 52:07 for 10K, 1:55:00 for a half marathon and 3:59:47 for a marathon. Longer predictions assume you have trained for the distance.

VO2 max from a 12-minute run

The Cooper test estimates aerobic fitness from how far you run in 12 minutes: VO2 max = (meters − 504.9) ÷ 44.73. Running 2,400 m gives about 42.4 ml/kg/min.

Heart rate zones

The Karvonen method uses your heart rate reserve: target = resting HR + intensity × (max HR − resting HR). At age 35 with a resting rate of 65, max is about 185, so 70% intensity is about 149 bpm. Most easy running should feel conversational, in the lower zones.

Try the calculators

This guide is general information, not professional advice.