⚙ CALCULATOR

Gear Ratio Calculator

Enter the tooth counts along a train and get the total ratio, each wheel’s rotational speed, the resulting hand ratios and the error against the target. A train that is off by more than a fraction of a percent will not keep time.

Inputs

Centre wheel teeth (teeth)

Third wheel teeth (teeth)

Fourth wheel teeth (teeth)

Escape wheel teeth (teeth)

Target display

Ratio error

—

against 60:1

Total ratio—

Required—

Stage 1—

Stage 2—

Fourth wheel—

Escape wheel—

Daily error—

Suggested third—

Adjust the inputs to see a result.

What the numbers assume

The minute wheel and hour wheel form a separate 12:1 reduction driven by the cannon pinion, independent of the going train.
Ratio error above roughly 0.1 % produces visible timekeeping error — the hands simply arrive at the wrong moment.

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

Gear Ratio Calculator

Inputs

What the numbers assume

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