If you know the number of wheel teeth, it is easy to calculate the correct pendulum length and the beats per minute.

Change the items in the  yellow  boxes and see the Results below.

Calculator

BPM and Pendulum Length

Teeth in Movement:

Wheel Teeth

Pinion Leaves

 # of Wheels in Drive Train:

Escape Wheel:

5 Wheels

4th Wheel:

4 Wheels

3rd Wheel:

Center Wheel or Center Pinion:

Results:

Beats per Hour:

Beats per Minute:

Pendulum Length:

 in.

 cm.

Tips

It can be a challenge to count the teeth on a wheel without losing your place. Here are a couple of tips:

• With a magic marker, place a dot next to the tooth that you will start counting. Now you will know when to stop counting.
• If the wheel is out of the movement, run the wheel across a sheet of paper and count the holes.

Formulae:

BPM = 

W_E x W₄ x W₃ x W_C

P_E x P₄ x P₃

 x 2 ÷ 60

or,

BPM = 

W_E x W₃ x W_C

P_E x P₃

 x 2 ÷ 60

L_P = 

141120

BPM²

where,

• BPM is beats per minute
• W_E is the number of teeth on the escape wheel
• W₄ is the number of teeth on the fourth wheel
• W₃ is the number of teeth on the third wheel
• W_C is the number of teeth on the center wheel, or center pinion for a 4 wheel train
• P_E is the number of leaves on the escape wheel pinion
• P₄ is the number of leaves on the fourth wheel pinion
• P₃ is the number of leaves on the third wheel pinion
• L_P is the pendulum length

5 Wheel Drive Train

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4 Wheel Drive Train

This calculator, provided by Horology - The Index, is one in a series of repair calculations.