If you are shopping for a leaf blower, then you’ve probably come across these measurements: CFM and MPH.
But what do they mean? Is there a difference between the two measurements?
What do these numbers tell you about the leaf blower you are considering buying?
Yes, there is a difference.
In fact, they both measure distinctly different things. And to understand this, we first need to understand what each of the measurements is.
Looking for a new leaf blower? Check out the following guides:
What Is CFM?
CFM stands for cubic feet per minute.
CFM is a measurement of how much air is pushed out the leaf blower pipe in a minute.
So, it is a measurement of volume.
What is MPH?
MPH stands for miles per hour.
Now MPH is the difference because it is a measurement of speed.
It measures how fast the air leaves the leaf blower pipe.
What’s The Difference Between CFM and MPH?
As we just stated, the difference is the fact that we are measuring two different things: speed and volume.
The CFM and MPH are affected by many factors in a backpack leaf blower’s design, such as:
- Motor type (2 cycle, 4 cycle, electric)
- Motor size (cc’s or watts)
- Impeller type and design
- Exit pipe design
How Does CFM Affect Leaf Blower Performance?
CFM (cubic feet per minute) measures the quantity of air, so it is a direct measurement of how much air is pushed out the leaf blower pipe.
The higher the CFM, the more material your leaf blower will be able to blow away. In short, a leaf blower with a higher CFM will blow away more material than a blower with a lower CFM.
If you could imagine a huge pile of leaves on the ground. A blower with a higher CFM rating would blow the pile away quicker than a lower CFM rated machine.
How Does MPH Affect Leaf Blower Performance?
MPH (miles per hour) is a measurement of velocity. This is how fast the air is pushed out of the leaf blower pipe.
The MPH of a leaf blower is a little harder to quantify, but basically, it means that a machine with a higher MPH will blow away debris more quickly and further than a blower with a lower MPH.
So What Does That Mean?
Basically, what it means is that you need to look at the two numbers together.
Ideally, you want to buy a leaf blower with as high a CFM and MPH as you can fit into your allocated budget.
In short, these numbers are a measurement of how much work you can do and how fast. So in this case, bigger is generally better.
Calculate The Leaf Blower Blowing Index
A good way to get a general overview of the performance of the leaf blower you are considering is to use the blowing index calculation.
We can calculate the blowing index as follows:
(CFM x MPH) x 0.0001 = Blowing Index.
e.g. 756 CFM and 234 MPH = 17.69
So a blowing index of 17.69 gives us a handy number to then compare against other models we are considering.
Blowing Index Calculator
You can use this calculator to easily work out the blowing index of any leaf blower.
Be Wary of Manufacturers Specifications
It is worth taking note of the fact that it is very easy for manufacturers to artificially inflate these specifications.
e.g. a manufacturer can easily increase the MPH of a unit by reducing the pipe size. But this in turn will reduce the CFM.
A good way to think of it is to imagine a water hose. If you have a low pressure problem, you can increase the distance that the hose will spray by decreasing the hose diameter.
When reading specifications of leaf blowers, be sure to take note of any caveats that are listed against the MPH or CFM specs. e.g. an MPH speed may be given while using a particular attachment – which is a good indication it is artificially inflated.
