Strava estimated power vs real

I've always wondered if the Strava estimated power was close to real power. So on a couple of specific segments I've run my phone using Strava and my Garmin using a power meter so that I can compare.

You can see from the screenshots below the differences.

In summary for smaller segments it was within 5%, drifing out to 13% on a 20 minute section, so you would assume it would drift further out for a full ride, something I will try in the near future. Interesting side note that the phone often gave me a second quicker time....

|
Langbar Reverse |
20:55 |
246 |
214 |
-13% |

|
Roker Lane |
02:30 |
367 |
356 |
-3% |

|
Crekeld Lane |
05:41 |
299 |
288 |
-4% |

Langbar Reverse

Roker Lane

Creskeld Lane