Power Reserve
Power reserve is how long a fully wound mechanical watch keeps running off the wrist. On most automatics it is around 40 hours; some movements reach 70 hours and more.
Power reserve is how long a fully wound mechanical watch keeps running once it comes off your wrist. The energy is held in the mainspring, a coiled strip of metal inside the movement, and the rate at which that spring unwinds governs how many hours the watch survives untouched.
Why the typical figure sits near 40 hours
A classic automatic watch normally offers around 40 hours of reserve. That is ample for a watch worn every weekday, yet it conceals a familiar snag: set it down on Friday evening and the watch may well have stopped by the time you reach for it on Monday morning.
How a longer reserve solves the weekend gap
Longer-reserve movements are designed precisely to close that gap.
- 40 hours: standard daily wear, liable to stop over a weekend off the wrist
- 60 to 80 hours: bridges Friday to Monday, so it is still running when you put it back on
- Reserve indicator: some watches add a dial hand showing exactly how much energy remains
To see how these traits vary across calibres, browse the Movement category, and for a well-known automatic diver, read the Orient Mako 3 review.
Related terms
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Frequently asked questions
What happens when a mechanical watch runs out of power reserve
It simply stops. Once the mainspring has spent its energy there is nothing left to drive the movement, so you need to wind it again, or wear it for a while if it is automatic, and then reset the time.
Is 40 hours of power reserve enough
It is ample for a watch you wear every day, but it can stop by Monday if it sits off your wrist all weekend. If you want it to bridge Friday to Monday, a 60 to 80 hour reserve is far more practical.
What does a power reserve indicator do
It shows how much energy remains on the dial. The hand lets you tell at a glance whether the watch is about to stop, so you can wind it before it does.