Before you shop for a chainsaw, consider the work you plan to do. The size and type of the wood you need to cut and your experience using a chainsaw are all factors in selecting the right saw.
Bar length is one way to judge a saw's size and the work it can handle. A saw with a longer bar can cut larger-diameter wood in a single pass. Bar lengths for most homeowner saws range from 6 inches on smaller electric saws to 20 inches on larger, gasoline-powered models. Professional-grade saws have bar lengths greater than 20 inches.
Engine displacement (gasoline-powered models), voltage (cordless models), amperage (corded models) and horsepower also relate to power and capability. The higher the numbers, the more power the saw has. Power matters most if you're working with large trees and branches or cutting hardwood timber such as oak or maple.
A longer bar and bigger motor or engine mean increased weight — something to consider if you need to use the saw for extended periods. Larger saws also create more vibration, take more effort to handle and increase safety concerns. A smaller, less powerful saw will be more manageable, particularly if you don't have much experience.