What is Critical Power in running?

Critical Power (CP) is the highest power output you can sustain for a long duration without fatiguing — roughly your one-hour power. It is the running equivalent of a cyclist's FTP and anchors all five power zones as percentages of itself.

Why use power instead of pace?

Power responds instantly to hills, wind, and surface, while pace lags and is distorted by terrain. Holding a steady power target keeps your physiological effort constant whether you are climbing or descending, which pace alone cannot do.

What percentages define the zones?

This tool uses a common five-zone model: Zone 1 below 80 percent of CP, Zone 2 from 80 to 90, Zone 3 from 90 to 100, Zone 4 from 100 to 115, and Zone 5 above 115 percent. These bands mirror the widely used Stryd power zone framework.

Is running power comparable to cycling power?

No. Running power meters estimate the metabolic cost of running and read lower than your cycling power for the same effort. Never compare the raw watt numbers across sports — only the zones relative to each sport's own threshold are meaningful.

How often should I retest my CP?

Retest every four to six weeks of consistent training, or after a clear fitness change. As your CP rises, all five zones shift up with it, so stale CP values will make your zones too easy.

Running Power Zone Calculator

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Running with power instead of pace lets your training intensity stay honest on hills, into headwinds, and on soft ground. This calculator takes your Critical Power and splits it into the five standard training zones so you can run by watts.

How it works

Every zone is a percentage band of your Critical Power (CP):

Zone 1  Recovery / easy      < 80% of CP
Zone 2  Endurance            80% – 90% of CP
Zone 3  Tempo                90% – 100% of CP
Zone 4  Threshold / interval 100% – 115% of CP
Zone 5  Anaerobic / sprint   > 115% of CP

CP itself sits right at the top of Zone 3, the boundary between sustainable aerobic work and efforts that accumulate fatigue. Because power reflects the mechanical work you are actually doing, a zone target holds the same physiological demand regardless of gradient.

Example and tips

With a CP of 280 watts, Zone 2 endurance runs fall between roughly 224 and 252 watts, while threshold intervals sit between 280 and 322 watts. Spend the bulk of your weekly volume in Zones 1 and 2, reserving Zones 4 and 5 for shorter, structured sessions. If your power readings look noisy on very short or very steep efforts, average over at least 30 seconds before judging which zone you are in.