Meadows & Passmore's Clock Mainspring Length Calculator ©

The length of a mainspring can be calculated for an empty barrel as follows:
The spring should occupy 1/3 to 1/2 of the space. The calculation assumes 1/2.

Length = ((((PI x (D/2)2)-(PI x (d/2)2)))/2) /t

At least 80% of the maximum suggested length should be used.

Three dimensions are required to select a spring:
A. Height or width in mm.
B. Strength or thickness in mm.
C. Internal barrel diameter in mm.
Determining the spring length by measuring the length of the one fitted is not recommended as it may have been
shortened as a result of a previous fracture.

Enter the measurements shown in metric or inches (but not mixed!)
 e.g.    D = 50      d = 15         t = 0.4

Barrel diameter (D)        
Arbor diameter (d)          
Spring thickness (t)   (no trailing zeros)

       

 

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