How to calculate running pace
Your pace is how long it takes to cover one unit of distance. It's calculated as total time ÷ distance. For example, running 5 km in 25 minutes is a pace of 5:00 per km.
Predicting race times
The Riegel formula predicts your time at a new distance from a known one: T₂ = T₁ × (D₂ ÷ D₁)^1.06. The 1.06 exponent reflects that you slow down slightly as distance increases. It's remarkably accurate for well-trained runners across 5K to marathon.
Why is my predicted marathon slower than 8× my 5K?
Because endurance fades over distance. The formula accounts for that natural slowdown, so longer races are predicted at a slightly slower pace.
Pace vs speed — what's the difference?
Pace is time per distance (min/km); speed is distance per time (km/h). They're two views of the same thing.