One of the things I like about back pack blowers, is that unlike many other power equipment products, their performance can be measured and compared. Never the less it can still become confusing as manufacturers will often throw out irrelevant numbers as will be explained below.
The measure. CFM (cubic feet per minute) and MPH (Miles per Hour) are the measures of blower performance. Manufacturers can easily increase MPH by making the pipe smaller but this will decrease CFM. And they can easily increase CFM by making the pipe bigger but this will decrease MPH. It’s not unusual to see manufacturers list CFM at the housing or MPH at the end of the pipe with some snap on nozzle that reduces the size of the outlet. These are cheats to artificially inflate the specs to look better than they really are. Beware when you see words like “housing” or “Max” or “with attachment”. What matters and what you are looking for is CFM and MPH measured at the same point at end of the pipe.
How do you measure performance with two different numbers. You can crate a blowing performance index by multiplying the two together. For example: If you multiply 700CFM @ 200MPH and drop a few zeros you get a blowing index of 14. It's not a perfect measure but a good estimator of one blowers performance against another.