Created By : Sunil Kumar Gandipadala

Reviewed By : Rajashekhar Valipishetty

Last Updated : Apr 10, 2023

Belt Length Calculator is a free online tool that computes the belt length be it ribbed, flat, timing or v-belt. All you need to do is enter the input parameters like large pulley diamter, small pulley diamter, centre distance and tap on the calculate button to find the belt length in no time.

Diameter of the large pulley:
Diameter of the small pulley:
Pulley centre distance:
Belt length:

Steps to Compute Belt Length

Follow the below mentiond steps to evaluate the belt length and get the result easily. They are in the following fashion./p>

  • Firstly, evaluate the dimater of large, small pulleys, distance between pulley axles.
  • Later, compute the sum and difference between pulleys, square of distance between pulley axles
  • Substitute the values found in the Belt Length Formula and determine the belt length.

Belt Length Formula

Know how to calculate the belt length by using the below listed formula for belt length in a two pulley system. Substitute the diamters of the pulleys and distance between the axles and find out the belt length.

Belt Length = ((DL+DS)*π/2) +(DL-DS)*arcsin((DL-DS)/2L)+2*sqrt(L2-0.25*(DL-DS)2)

Where DL means diamter of the large pulley

DS means diamter of the smaller pulley

L stands for distance between pulley axles


Question: Compute the belt length of a two pulley system if the diameters of the large pulley is 25m and smaller pulley is 15m and Distance between the pulley axles is 21m?


Given that

Diamter of Larger Pulley DL = 25 m

Diamter of the Smaller Pulley DS = 15 m

Pulley Centre Distance L = 21 m

We know the formula to find the belt length is given by Belt Length = ((DL+DS)*π/2) +(DL-DS)*arcsin((DL-DS)/2L)+2*sqrt(L2-0.25*(DL-DS)2)

Input the values in the formula as long as all the metrics are in same units or else change them all into similar units.

Substitute the input values in the belt length formula and we have the equation as follows

Belt Length = ((25+15)*π/2) +(25-15)*arcsin((25-15)/2*21)+2*sqrt(212-0.25*(25-15)2)

Simplifying the equation further we have


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Another Belt Length Formula

If you don't have time and can go for an approximate calculation of belt length you can use this alternative formula and find out the belt length easily.

Belt Length = ((DL+DS)*π/2) +(2*L)+(DL-DS)2/(4*L)

Where DL means diamter of the large pulley

DS means diamter of the smaller pulley

L stands for distance between pulley axles

You can use this simplified formula when you want to make faster calculations. However, this formula fails if one pulley is larger than the other or both of them are closer together.

FAQs on Belt Length Calculator

1. What is meant by Belt Length?

Belt Length is the length spread out between two pulleys in which the pulleys are of unequal radii.

2. What does DL and DS stand for in the Belt Length Formula?

DL and DS are nothing but the diamters of the larger pulley and the smaller pulley.

3. What is the formula to determine the Belt Length?

The Formula for Belt Length is given by Belt Length = ((DL+DS)*π/2) +(DL-DS)*arcsin((DL-DS)/2L)+2*sqrt(L2-0.25*(DL-DS)2)