⚙ CALCULATOR

Power Reserve Calculator

From barrel dimensions, spring geometry, gear ratios and consumption, estimate theoretical and realistic power reserve, when the rate starts to drift, and how often to wind.

Inputs

Barrel inner diameter (mm)

Mainspring length (mm)

Mainspring thickness (mm)

Barrel to centre ratio (:1)

Beat rate (vph)

Transmission efficiency (%)

Power reserve

—

hours, realistic estimate

Theoretical—

Turns of wind—

Barrel speed—

Torque, full—

Stored energy—

Mean draw—

Barrel fill—

Beat rate—

Adjust the inputs to see a result.

What the numbers assume

Amplitude falls as the spring unwinds, and rate drifts with amplitude. The last quarter of a stated reserve is usually where the watch stops keeping its best time.
An automatic movement only reaches full wind if it is worn enough; a winder is a convenience, not a substitute for a movement in good order.

These are estimates from the values entered, given to make the relationships visible. They are not measurements, and they do not certify a movement. Verify against the actual movement and its service documentation.

⚙ RELATED

Power Reserve Calculator

Inputs

What the numbers assume

Read next

Mainspring Barrel

Automatic Movement

Manual Wind Movement