Automatic winding - what sort of ratio hours-wear : hours-power do manufacturers aim for?

Sorry if this is a stupid question, but I've never thought about it before, and can't find much if anything online.

I just picked up and put on an automatic that was very close to end-of-power-reserve, and because it has a screw-down crown I thought I'd avoid wear & tear on the crown tube and just wear it for a while.

The question that occurred to me is: "how long do I need to wear it in order to put at least e.g. 8 hours on the power reserve so it can keep going overnight?"

I'm sure it varies a lot between manufactures and calibers (this is a Rolex 3230), but I'm curious to know are there industry targets / conventions that manufacturers aim to achieve for hours-wear : hours-reserve. Perhaps our resident watchmakers can chip in?

Thanks Dan - interesting about the watch winders, I'd not thought of that as a possible source of data.

I bet auto movement manufacturers have some sort of range they expect. Hopefully the activity level is set lower than desk-jockeys like me can muster!

I was talking about this sort of topic with a friend who said that he wasn't active enough on a daily basis to prevent his automatic watch from eventually stopping overnight. We started ruminating about how in the absence of a power reserve meter an individual would measure an average power consumption/regeneration of their daily routines. Assuming you can kind of tell when the watch is fully wound (thanks again to the folks here who educated me on the bridle parts of an automatic mechanism), that would be the obvious starting point. Then assuming you can accurately measure how many crown turns it takes to go from fully stopped to fully wound, that would be another base measuring point. Another would be the actual power reserve time from fully wound to fully stopped. So then you could at the end of each day measure how many turns it takes to get from the partially depleted state to the fully wound state again, and the fraction of the total number of crown turns relative to the turns needed to wind from empty to full could be a measure of what percent you're expending in the day?

I only have two automatics. One makes a just audible click when it is fully hand wound -- that's the Speedy Reduced. The other, a Hamilton 1969 Cal 11 gives no indication, but I found that 8 hours of wearing gives 48 hours of running starting from fully unwound, so I don't think it matters.

All interesting stuff!

@Donn Chambers So 4 hours of auto winding provided 4 hours of runtime, plus an excess reserve of 1 to 2 hours (+25% to +50%), perhaps call it +33%. Thanks for putting a range on it, and after a bit of thought that strikes me as a little low…

My reading of a manufacturer’s reserve is that one could pick up the watch at any point before the end of that reserve, and expect to continue indefinitely without needing to wind it up full. So I suppose we could think about this from the other angle of how many hours /day will the watch be worn, so what ratio does the mfr need to create in order to keep it from depleting over subsequent (unworn) nights…. Call it 8 hours sleeping unworn, so a nearly unwound movement at morning will get picked up and worn, and has a maximum opportunity of 16 waking and worn hours to make it through the following night, so a minimum ratio of (8/16) +50% should work.

I guess one might want a large margin of error on that, so perhaps assume 8 hours waking & worn, for a ratio of (16/8) +200%. Or maybe more, if one thought that the wearer might alternate days e.g. ((24+16)/8) +500% …. Hmm. Maybe there’s no specific answer here, ha

I guess it all depends on your level of activity, in my case I only have to wear an automatic half a day or less for it to get a full wind.
I think of my self as fairly sedentary but that's obviously not true as I can never sit still for long ( my perception is that I sit for too long).
My wife is always saying sit down and relax but F that, there is too much to do every day and I always seem to run out of time.

While driving my car from home to office for 40 minutes having both hands on steering wheel and negotiating Delhi traffic and turns, I wind my JLC to the full. Same I can say with my other automatic watches. Even a brisk morning walk for 45 minutes with hands moving both ways has the same results.

That's a great idea - thanks! Will give it a try and report back