Power Reserve Explained: How Long Will Your Watch Run?

The power reserve is the length of time a fully wound mechanical watch will run before it stops. It is one of the most useful numbers on a spec sheet, because it tells you how long you can leave a watch in a drawer before it needs resetting.

A lot of standard automatic movements offer about 38 to 42 hours. That is enough for a weekend off the wrist, but not for a week. Many newer movements are built for 70 to 80 hours or more, and a few go to eight days or beyond with multiple mainspring barrels.

Longer reserves come from a longer mainspring, from several barrels working in series, or from lower-frequency, more efficient designs. Some brands also use new alloys for springs that give more torque for longer.

Accuracy can change as the spring unwinds. A mainspring delivers slightly less force when almost run down, so the watch may run a little slower or faster toward the end of its reserve. Good regulation and a stable escapement reduce this effect.

Some watches display the reserve on the dial with a small indicator. It is a handy complication for hand-wound watches, because it tells you when to wind and prevents overwinding anxiety.

When comparing models, treat power reserve as a convenience feature. If you rotate between watches, a longer reserve means fewer resets, and it is a real quality-of-life upgrade.