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Calculate the Needed Change in Pendulum Length

If your clock is ticking away but its a little slow or fast, use this calculator to determine how much to shortern or lengthen the pendulum. You don't have to be too precise on the current length; if you have a fairly close figure, then the needed change will be close too.

Change in Pendulum Length
Current Pendulum Length
How Fast or Slow is
the Clock Currently?
Fast, orin 24 Hrs:
Slowin 1 Hr:

Beats per Hour:
Beats per Minute:
Pendulum Length:inches
Needed Pendulum Change:  inches

The center of gravity includes the mass of the pendulum bob and the pendulum shaft. However, with this calculation of determining the needed change in pendulum length it is really only important to measure the estimated center of gravity in exactly the same way each time.


BPM = (141120 ÷ LP)½

  • BPM is beats per minute
  • LP is the pendulum length
Pendulum Length

This calculator, provided by Horology - The Index, is one in a series of repair calculations. This calculation may be used by anyone who wishes to adjust a pendulum clock to be faster or slower.

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