Buying the right leaf blower is not as simple as it seems. There are a variety of specs that are promoinently displayed on the box for every blower out there. The main specs are the blower’s maximum CFM and MPH capabilities, but what do these actually mean, and which of them is most important?
In this article I’d like to take the time to explain the difference between CFM and MPH and explain which one is most important and why you might consider one over the other.
Leaf blowers are rated by the amount of air they move which is measured in cubic feet per minute (CFM). They are also measured by the speed at which they move that air measured in miles per hour (MPH). Larger more powerful blowers can move more air faster than smaller blowers but the tube size and shape play a role as well. Wider tubes allow for higher CFM but at the sacrifice of MPH, conversely narrow tubes will push great MPH but less CFM.
In some ways CFM is like the flow of water in a hose and MPH is like the pressure of the flow measured in PSI, the speed at which the air is flowing gives a blower it’s strength but if CFM is low that strength will be isolated to a very small space. There are very specific reasons why this may be desired however but in most cases regular homeowners will be mostly concerned with the overall output of air and not the speed at which it’s delivered.
Let’s dive into this topic a little more in depth so I can explain the nuances of blower CFM and MPH specifications.
Is Leaf Blower CFM More Important Than MPH?
As you know, CFM and MPH are two entirely different things although they are related. Now, both of them combined are supposed to show the overall efficiency of a model, but only to a certain extent.
Which one is more important and which one should be the one that you should check out first? I recommend most people look to CFM first, here’s why.
Why CFM Is More Important (Most of the Time)
In the vast majority of cases a blowers ability to push more air out (CFM) is more important than any other factor… so long as velocity (MPH) remains high enough to actually move materials on the ground.
Most people use leaf blowers to gather leaves or to move leaf piles in the fall but they also use them to clean sidewalks and driveways from dirt and grass clippings throughout the growing season after mowing and trimming sessions.
Basically the average tasks a blower is responsible for require only decent force and a wide swath of air to accomplish. When you are cleaning a sidewalk you want your blower to clean it in one pass; you don’t need it to blow narrow stripes extrodinarily hard, you just need it to deliver just enough force to clean the walkway in as short of a time as possible.
The same can be said for autumn leaf cleanup jobs. If a tree drops a bunch of leaves all over your lawn in October or November you want your blower to cover a wide area on each pass with enough force to move the loose leaves easily and quickly. For freshly fallen leaves you don’t need extreme velocity to get this job done. If your blower can cover a wider area with decent velocity you’ll actually be happier than if it covered narrow strips with super strong velocity.
In most situations your blowing job will be done faster and at a lower volume if you use a blower that has a higher CFM and lower MPH rating.
When High MPH Ratings On Your Blower Matter Most
MPH, on the other hand stands for “miles per hour” and as you might have guessed, this is a much clearer indication of of the speed of the air, the velocity. The higher or lower your MPH is, the faster the air would be coming out of your leaf blower and the more potential power it has to move heavier, wetter, or stuck objects.
Think about wet matted leaves in the month of December… or February for that matter. If you never were able to clean up the yard in the Fall all the leaves that remain at the end of winter will be matted down and stuck to the ground. You need more wind force to dislodge them and that’s where higher MPH numbers become important.
In other settings the MPH number also becomes more meaningful when you are dealing with wet debris or heavy yard debris like pine needles, cones, and even dirt of gravel that may find it’s way onto a sidewalk or driveway.
Most of the time the high MPH capabilities of a blower will be handy in “out of the ordinary” situations so buying a blower based on this number will be less helpful to you over a normal season.
Most blowers are designed to have adequate air flow or velocity for the CFM that they push and they are also designed to be run most of the time at lower speeds for basic every day chores. Turbo buttons or high speed options are common on leaf blowers of the gas, electric, and battery operated varieties for this reason.
In fact, many times the higher velocity leaf blowers are unwelcome. No one want to ruin a flower bed just because the air flow on a leaf blower was too fast.
To sum it up, MPH is an indicator of the speed at which air comes out of your leaf blower. It, however, does not indicate anything other than the speed – so you don’t know how much air is coming out or anything else about it.
How Leaf Blower CFM & MPH Are Inversely Coorelated
Why don’t blowers that have extremely high MPH specifications also have extremely high CFM specs? Because of physics mostly.
It’s simply harder to push a greater volume of air faster. Smaller volums of air can be more easily moved extremly fast. In fact of you took the same motor on a blower and installed a narrow air output on it the volume of air expelled would be less but the velocity of that air would be greater.
Once the exit tube is widened the same amount of air or more can exit the blower but it won’t come out as quickly because it doesn’t need to. To keep the velocity up the motor has to work harder and harder and with small outdoor tools the tool would have to get bigger, bulkier, and more expensive to keep up with the MPH demands as the CFM output increases.
There’s a reason why the best leaf blowers on the market are expensive. To get high CFM and MPH ratings the machines simply cost more to produce. For battery blowers with high CFM specs the cost can get quite high indeed.
How Leaf Blowers Work
Most blowers work based on a motor or engine turning an impeller or a turbine. As the impeller spins air is sucked into the unit through a set of vents usually near the motor or handle. The blades then propel the air through a narrow shaft which increases it’s velocity at the exit point.
The strength of the motor or engine (and the air intake vents) have everything to do with the amount of air a blower can move. Considering the strength of the motor and adequate air intake the cubic feet per minute a blower is capable of pushing is further defined by the exit point – outflow points and their tubes that are wide will allow for greater CFM however the wider it gets the MPH decreases. Eventually an inflection point occurs. When the exit point gets too wide the MPH will get too low resulting in a blower that can’t get any legitimate work done.
The sweet spot is where most people want to be, a blower that can produce between 250 to 500 CFM with over 100 MPH wind speed. Most modern blowers operate at low speed near the bottom of these thresholds and work just fine. Turbo buttons and options allow these motors to ramp up to full power potential which is usually more powerful than ordinary household jobs call for.
Now that we know what to look for in terms of power, we should take a look at which leaf blowers are going to be the most productive.
Which one is more important of the two?
Well, let’s get to the real question now. How strong of a leaf blower do you actually need?
In my home and on my website and YouTube channel I am a huge proponent of battery powered equipment. I think they are the smarter product to own for the long term due to their lower maintenance costs and their eco-friendliness.
For most people living in regular domestic settings and using their blowers like regular homeowners a blower doesn’t usually have to be the most powerful unit available to be worth buying.
I recommend most of my readers to opt for something middle of the road. Stay away from the blowers that can’t push more than 500 CFM on the high or turbo setting but also stay away from blowers that are meant for commercial applications, in most cases they are stronger (and more expensive) than the average person needs.
Remember, having faster air velocity is helpful when trying to move heavier or wet debris. The volume of air moved is more important usually because most settings where you use a blower you are dealing with lots of debris covering a larger surface area.
Blowing It All Into a Pile (aka The Conclusion)
For people looking to buy a leaf blower it’s important to see MPH specs high enough to do normal tasks like moving dry leaves, cleaning up grass clippings, and cleaning loose dirt off of driveways and sidewalks. Almost every low end leaf blower will do these jobs just fine.
The higher the stated MPH ratings go the faster velocity the air will move which can make it easier to move heavy, wet, or ground in debris from whatever surface you are blowing. Most people however will not need or want the highest MPH blowers however unless it is paired with extremely high CFM specs. The reason being that blowers that can blow air at a higher CFM will be easier and faster to use in normal circumstances. You won’t have to have direct line of airflow pointing at what you are trying to move when the CFM is higher. The air dispersed will cover a wider swath.
Shop for high CFM blowers first, then look to high MPH ratings as a secondary measurement before you choose anything… and above all, if you care about my opinion to any degree, consider opting for a battery powered option over gas. You can see my reviews of the best battery powered blowers in a future article.
While you’re waiting for that article, you might want to check out the following articles instead: