The pitch of your chain:

This is the actual size of the links. If you wanted to find out the pitch of your chain using a ruler or measuring tape, you would measure the distance between any 3 consecutive rivets on the chain and divide by two. The smaller the saw, the smaller the pitch! There are many pitches of chains, the most popular are: 1/4 - .325 - 3/8LP - 3/8 - .404

The gauge of your chain:

The Gauge is the thickness of the drive links. The drive links are the part of the chain that sit inside the groove in the bar. There are also many different gauges including: .043 (1.1mm) .050 (1.3mm) .058 (1.5mm) .063 (1.6mm)

The length of your chain:

This is measured by the amount of drive links on the chain. As mentioned previously, these sit inside the groove in the bar. Count the number of drive links to determine the length of your chain.