Lots of variables, as other folks mentioned. I don't use a power meter but I've noticed my Strava guesstimates are awfully close to the folks I know who do use power meters and are about my size, weight, etc. The main difference is most of them are riding lighter bikes. But it's close enough within 10 watts, give or take. I'm mostly interested to see that I'm gradually holding a little more power over distance and on some difficult segments compared with last year, on the same bike and weighing about the same. Good enough for my purposes. I don't need a power meter to remind me that I'm still a slug compared with most guys my age.