Pace Every Kilometer,
Predict Finish Line Times.
Free running calculators: predict race times with the Riegel formula, build training pace zones, generate split tables, and convert pace to speed. No sign-up.
Pete Riegel Power Law
Mathematically validated race projection model accounting for fatigue curves from 5K up to marathon.
5 Heart Rate Training Zones
Zone 2 base endurance (60–70% max HR) versus threshold tempos and VO2 max track intervals.
Negative Split Pacing
Pacing strategy charts designed to hold energy in reserve for an aggressive, fast finish.
PaceKeeper Calculators
Race Time Predictor
Predict your time at any distance from a recent result — Riegel's formula with honesty labels on long extrapolations.
Training Pace Zones
Five training paces derived from your recent race — easy, marathon, tempo, interval, and repetition — with what each one is for.
Race Split Table Generator
Mile-by-mile (or km-by-km) splits for your goal time — even pace, negative split, and the wall-risk of going out too fast.
Pace & Speed Converter
Convert pace per mile ↔ per km ↔ speed in mph/kmh ↔ treadmill settings — with race-equivalent context.
Evidence-Based Physiology
The Riegel Formula: How to Predict a Race From Another Race
T₂ = T₁ × (D₂/D₁)^1.06 — one equation powers every race predictor. Where it comes from, when it lies, and which exponent to use.
80/20 Running: Why Your Easy Days Are Too Fast
Elite runners spend ~80% of training below their aerobic threshold. Most recreational runners manage barely 50% — and wonder why they plateau.
Marathon Pacing: How the Race Is Actually Won in the Last 10K
The marathon rewards patience with interest. Course anatomy, the glycogen math, and split strategies from even pace to the negative split.