You finish a hard ride and check your data. Average power reads 185w, but your Weighted Power shows 215w. Which one reflects your actual effort? Understanding the difference between these metrics is crucial for effective training analysis.
Why Is Weighted Power Higher Than Average Power?
Average power simply divides total work by time. While mathematically straightforward, it has a significant limitation, because it doesn't account for the physiological cost of variability.
Consider two hypothetical one-hour rides.
Ride A. Steady 200w the entire time
Ride B. Alternating 5 minutes at 300w, 5 minutes at 100w
Both rides average exactly 200w. But Ride B is dramatically harder. Those 300w surges create disproportionate fatigue, require anaerobic contribution, and demand more recovery, none of which the simple average captures.
This is why we need Weighted Power.
What is Weighted Power?
Weighted Power estimates the power you could have sustained for the same physiological cost if you'd ridden at a completely steady effort. It's an "equivalent steady-state power."
For variable rides, Weighted Power will always be higher than average power. The more variable your power, the larger the gap.
What matters is that strain rises far faster than power once you go above threshold. Oxygen cost climbs roughly in step with watts, but lactate, glycogen use and fatigue climb much more steeply, and Weighted Power's weighting is a practical approximation of that.
How Weighted Power is Calculated
The Weighted Power algorithm works in four steps.
- Calculate a 30-second rolling average of power
- Raise each value to the 4th power
- Take the average of all those 4th-power values
- Take the 4th root of that average
The 4th power exponent emphasises intensity spikes, so brief hard efforts have outsized impact on the final Weighted Power value.
You don't need to calculate this manually, because WattPlan computes Weighted Power automatically. But understanding the mechanism explains why it behaves as it does.
When Weighted Power and Average Diverge
Small Gap (< 5% difference)
Scenario. Steady riding such as time trials, long climbs and indoor trainer workouts
When power is constant, Weighted Power and average converge. A perfectly steady ride would have identical values.
Moderate Gap (5-15% difference)
Scenario. Undulating terrain, moderate group ride, threshold intervals with recovery
Most structured training falls in this range. Some variability exists but overall effort is controlled.
Large Gap (15-25%+ difference)
Scenario. Criterium racing, group rides with attacks, hilly routes with repeated surges
High variability creates significant gaps. A criterium might average 180w but have Weighted Power of 230w due to constant accelerations and recoveries.
Intensity Explained
Intensity compares your Weighted Power with your FTP.
Intensity = Weighted Power / FTP
| Intensity | What It Means |
|---|---|
| < 0.75 | Easy, recovery pace |
| 0.75-0.85 | Moderate endurance effort |
| 0.85-0.95 | Tempo to sweet spot |
| 0.95-1.05 | Threshold effort |
| > 1.05 | Above threshold (only sustainable briefly) |
Intensity above 1.0 is possible for shorter efforts. A well-paced 20-minute FTP test comes out close to 1.05, because FTP is taken as 95% of that effort. A 60-minute effort above 1.0 suggests your FTP needs retesting.
Intensity feeds directly into Training Load calculations, making it essential for tracking training stress.
Practical Applications
Pacing Races and Events
For steady events such as time trials, pace from your actual power and keep Weighted Power close to your average. If Weighted Power drifts well above average, you are surging, and surges cost more than they return.
Example. 250w FTP, targeting 238w for a 40km TT. Hold it as evenly as the course allows.
Analysing Group Rides
Average power on group rides is often misleading due to drafting and surges. Weighted Power better reflects the actual effort and fatigue cost.
A rider averaging 160w but with 210w Weighted Power worked significantly harder than one averaging 180w with 190w Weighted Power.
Evaluating Interval Workouts
For interval sessions, analyse both.
- Interval Weighted Power, to see whether you hit your targets during work periods
- Overall session Weighted Power, for total workout stress
Comparing Rides
When comparing rides across different terrain or conditions, Weighted Power provides better comparison than average, and it is what the Fitness Explorer builds on. A hilly ride with lower average power but equal Weighted Power to a flat ride represented similar physiological cost.
Weighted Power for Different Ride Types
| Ride Type | Avg Power | Typical WP | Difference |
|---|---|---|---|
| Indoor trainer workout | 180w | 185w | ~3% |
| Solo endurance ride | 170w | 180w | ~6% |
| Rolling hills loop | 175w | 195w | ~11% |
| Hard group ride | 165w | 205w | ~24% |
| Criterium race | 175w | 225w | ~29% |
Variability Index
The ratio of Weighted Power to Average Power is called Variability Index (VI).
VI = Weighted Power / Average Power
- VI of 1.0 is a perfectly steady effort
- VI of 1.05 is normal variation
- VI of 1.10+ is significant variability
- VI of 1.20+ is highly variable (racing)
VI helps identify ride characteristics. High VI might indicate any of these.
- Technical terrain with lots of coasting
- Group ride dynamics
- Poor pacing
- Racing with attacks and recoveries
Frequently Asked Questions
Which metric should I use for FTP testing?
Average power for FTP tests. The protocols assume relatively steady effort, minimising the Weighted Power/average gap. A 20-minute test should have VI below 1.05.
Can Weighted Power be lower than average power?
Theoretically no. In practice, data dropouts or sensor issues might create apparent anomalies. Valid data will always show Weighted Power equal to or greater than average.
Does Weighted Power account for drafting?
No. Weighted Power reflects your power output regardless of external factors. You produce less power while drafting, which shows in both metrics.
How does elevation affect Weighted Power?
Weighted Power doesn't directly consider elevation, but climbing naturally creates more variable power (harder on uphills, easier or coasting on descents), which affects the calculation.
Should indoor and outdoor rides have the same Weighted Power for the same workout?
Indoor rides are usually steadier, so Weighted Power sits closer to average than it does outdoors. Many riders also produce a little less power indoors, mostly because of heat. There is more on why indoor power often looks lower.
Weighted Power transforms messy, variable ride data into meaningful training metrics. Use it alongside average power to understand both what you did (average) and what it cost you (Weighted Power).