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 models reach 70 hours and beyond.
Power reserve is how long a fully wound mechanical watch keeps running once it leaves your wrist. The energy lives in the mainspring, a coiled strip of metal inside the movement, and the rate at which that spring unwinds decides how many hours the watch survives untouched.
Why the typical number lands near 40 hours
A classic automatic watch usually carries around 40 hours of reserve. That is plenty for a watch you wear every weekday, but it hides a familiar trap: take it off Friday evening and the watch may well have stopped by the time you reach for it Monday morning.
How a longer reserve fixes the weekend gap
Longer-reserve movements exist specifically to close that gap.
- 40 hours: standard daily wear, prone to stopping over a weekend off the wrist
- 60 to 80 hours: bridges Friday to Monday, so it is still ticking when you put it back on
- Reserve indicator: some watches add a dial hand that shows exactly how much energy is left
To see how these traits differ across calibers, browse the Movement category, and for a popular affordable 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 enough 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 is left 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.