Saws do not come with chains. Chains are purchased separately. The chains are measured by the number of drive links that are on the chain. The drive links are the thickest part of the chain. If you are replacing an old chain, you should be able to count the drive links on the old chain and purchase the same number of drive links on the new chain. The width of the drive links are what determine the size of the chain. You will want to make sure the drive links on the new chain are the same width as the drive links on the old chain. The drive links will be stamped on the side of the drive links with the words SST, D, R, XS etc. These are the industry standards for the width of the drive links. You will need to know the width of the saw bar. You will then need to choose the correct model of chain that fits the size of the saw bar.