May 082013

This page is a continuation of How to Design a Flat Belt Drive [Step-by-step Tutorial] – Page 1.

Step 3 – Finding Design Power in kW:

Design power in kW can be found out using the following equation:


Rated power in KW will be provided in the problem itself. To find the correction factors in the above equation, see the section below.

Determination of Correction Factors:

a. Load Correction Factor:

Load correction factor can be determined from the following table.

Table (i) – Load Correction Factor

 Type of Load Applications Load Correction Factor
Normal Load (When maximum load is known)  1.0
Steady Load Light duty fans, centrifugal pumps, printing machinery, textile machinery, screens, agitators, evaporators and light machinery  1.2
Intermittent Loads Heavy machine tools, heavy duty fans and blowers, air compressor, reciprocating pumps, elevators, mill machinery, line shafts, paper mill and saw mill machinery  1.3
 Shock Loads Hammers, grinders, crushing machines, disintegrators, vacuum pumps, rolling mills, tube mills, ball mills, automated machinery and stamp presses  1.5

Note: If you are using PSG design data book, refer page no. 7.53 (May 2012 reprint) for this table.

b. Arc of contact factor:

In order to determine arc of contact factor, you must first find the arc of contact. Arc of contact can be determined using the following equation:



D → Diameter of the larger (driven) pulley

d → Diameter of the smaller (driving) pulley

C → Centre distance between the two pulleys

Note: If you are using PSG design data book, refer page no. 7.54 (May 2012 reprint) for this equation.

After finding the arc of contact, you must change it to the nearest standard value (greater than the one determined) and find its corresponding correction factor. The following table will help you do this.

Table (ii) – Arc of contact factor

 Arc of Contact Arc of Contact Factor
 90°  1.68
 120°  1.33
 130°  1.26
 140°  1.19
 150°  1.13
 160°  1.08
 170°  1.04
 180°  1.00
 190°  0.97
 200°  0.94
 210°  0.91
 220°  0.88
 230°  0.86
 240°  0.84
 250°  0.82

Note: If you are using, PSG design data book, refer page no. 7.54 (May 2012 reprint) for this table.

c. Smaller Pulley Diameter Factor:

Smaller pulley diameter factor can be found using the table below:

Table (iii) – Smaller Pulley Diameter Factor

Smaller Pulley Diameter (in mm) Smaller Pulley Diameter Factor
 Upto 100  0.5
 100-200  0.6
 200-300  0.7
 300-400  0.8
 400-750  0.9
 Above 750  1.0

For the fourth step (i.e., determining velocity of belt), go to next page.

Bookmark, Email or Share this Page

Get Fresh Content from!

Written by

I am a mechanical engineer with a passion for technical stuff. I am the founder and former editor-in-chief of

  • Varadha Yamunan

    Good one :) Helped me pretty well.. Thank you

    • Surjeet S

      You are welcome… Get fresh content from by liking us on facebook and subscribing to our e-mail newsletter :)
      Our facebook page:

  • pradeep patil

    While designing belt drive set the centre height of both pulley shall be same?
    what is effect on power transmission if their is height difference?

    • Surjeet S

      The heights of the pulley centers from ground depend on the height difference between the driving and driven shafts. They may or may not be the same. If there is a height difference, the centre to centre distance (between the pulleys) increases. This will have a direct impact on the arc of contact and the design power we calculate.

      • Sarungbam Romen Singh

        Hello Surjeet,
        In the Book “Design of Machine elements” by VB Bhandhari, the arc of contact factor, Fd is multiplied with the rated power while as per the formula you’ve referred here, the said factor divides the rated power.
        [Corrected Power= {(load correction factor x rated power) x arc of contact factor}]
        Please clear me this confusion I m having with.
        I am just an Electrical Engg. Student working on the flat belt drives.
        Thanking you in anticipation.

  • Ron Verduguez

    can you give the references of the equations that you used on this design? thank you…

    • Surjeet S

      These equations can be found in any standard design databook. In India, we normally follow PSG Design Databook

      • Ron Verduguez

        thank you…

  • Dineshraj Srinivasan

    can you give design calculation for the v-belt drives ?

  • Hem Shailabh

    Hi! Can you tell me why the product of coefficient of friction and angle of wrap is minimized when designing open belt drives for certain maximum stress? Please reply asap. @Surjeet_S:disqus I am yet to start studying DME, i asked this from my knowledge of Kinematics-OM. Thanks

  • Eng Medson Naftal

    Thanks i understand well