Many times when a mechanic has to change our chains, there is no way of knowing how long the chain should be. One way is to lay the new chain down beside the old chain, but remember that the old chain has been stretched. 

Or, maybe you are installing a new drive and you want to have the chain made up before you install it. So, what do you do? 

One method is to take a tape measure and wrap it around the sprockets to get the chain length. However, this is not a very accurate way to determine the length. Instead, let’s take a couple of measurements, then use a simple formula to calculate the actual length that is needed. 

First, move the sprockets together until they are as close as the adjustments will allow. Then, move the motor or drive out ¼ of its travel. Now, we are ready to take out measurements. The following information is needed for an equation to find the chain length: 

1. Number of teeth on the drive sprocket. 
2. Center-to-center distance between the shafts.
3. The chain pitch in inches. 

Here’s an example: 

Now, here is the formula to solve the example above:

Use the formula above to find the chain length: