Plant Operations/Maintenance/Belt length


Hi Matt

Could you please explain how to calculate belt length


Bellt length formula
Bellt length formula  
Hi Bernie,

Accurate belt length is found with the formula from the link below:

Where D is the diameter of the large pulley, d is the diameter of the small pulley, and c is the center distance between shafts.

As an example, we take the formula belt length = 2C + 1.57(D-d) + ((D-d)x (D-d)/4C)

If we had a 6" pulley, and an 8" pulley on 20" centers, we would simply plug in the numbers and follow BEDMAS rules for calculations (Calculate Brackets first,  then any exponents, then division or multiplication, and finally any addition or subtraction)

For our example, we would then have:

2 x 20 + 1.57 (8+6) + ((8-6) x (8-6)/ (4x20)=



For approximate belt length, we would only use the first part of the equation:

2C + 1.57 (D+d)=

40+ 1.57(14)=


In both examples, 1.57 is used as a constant and is used because it is equal to half of pi (3.14)

Please let me know if you have any further questions.



Plant Operations/Maintenance

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Matt Bolger


I can answer questions you may have regarding Millwright trade exams such as power transmission, safety, fluid power, some welding questions, bearings, and rigging and hoisting, as well as a variety of questions about equipment maintenance. Troubleshooting questions are ok, but without physically looking at and testing the equipment (as there are infinite numbers of industrial equipment applications), these questions may be difficult to accurately answer.


I am a licensed industrial mechanic/millwright (Canada - C of Q red seal). I have 13 years experience as a Millwrigt, maintenance supervisor, maintenance manager and operations and engineering manager.

Millwright license (Red Seal). I have also written a millwright study guide and shop reference manual that was designed to assist mechanics in passing the millwright trade exam.

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