Removing the chain and the blade off a chainsaw is the best way to get the most accurate measurement of your chainsaw's bar. With a basic knowledge of tools and chainsaw parts, this task is relatively simple and will not take too much time to complete. This will allow you to also inspect the blade of the chainsaw for damage so that you can purchase a new bar if it is needed.
Remove the two nuts screwed into the casing located near the handle with a socket set. These two nuts secure the casing to cover the blade. Once you have removed the nuts, remove the casing. Behind the casing you will see the drive socket assembly, chain and bar of the saw.
Locate the tension wheel just inside the bar of the chainsaw. Use a flathead screwdriver and turn the screw towards the left to release some of the tension and pull the chain away from the grooves on the bar. Remove the chain from all the grooves on the bar until you reach the drive sprocket.
Pull the chain over the drive sprocket to remove the chain completely. The drive sprocket is a wheel located underneath the handle.
Pull off the blade or bar once the chain is removed. When you remove the bar you can check and see if the bar needs repairs or needs to be replaced.
Place the blade on a flat work surface and measure the bar or blade with a ruler. Measure the length of the bar from one end to the other or take your blade to a local hardware shop and they can get a new blade or measure the one you have for you.