🌬 Fan RPM to CFM Calculator
Estimate PC fan, case fan, radiator fan, and duct fan airflow from diameter, RPM, blade pitch, blade count, static pressure rating, pressure demand, restriction, radiator density, filter loss, and air density.
Static pressure is comfortably above the estimated path demand.
RPM and tip speed are in the normal gaming PC range.
This setup behaves like a filtered case intake.
Estimated speed per fan to reach the selected system target.
| Fan size | Common RPM | Open-air CFM | Typical role |
|---|---|---|---|
| 80 mm | 2000-5000 | 20-55 | Server, small form factor, exhaust slots |
| 92 mm | 1500-3000 | 25-60 | Compact CPU coolers and SFF cases |
| 120 mm | 900-2200 | 35-90 | Mainstream case, AIO, tower cooler |
| 140 mm | 700-1800 | 50-115 | Quiet case airflow and large radiators |
| 180-200 mm | 400-1000 | 80-180 | Large low-noise front intake |
Ranges vary by blade geometry, frame thickness, hub size, grill shape, and manufacturer rating method.
| Path | Retained airflow | Pressure demand | Calculator use |
|---|---|---|---|
| Open bench | 95-100% | 0.00-0.15 mmH2O | Fan spec comparison |
| Rear grille exhaust | 85-95% | 0.10-0.35 mmH2O | Low restriction cases |
| Fine mesh intake | 75-90% | 0.25-0.70 mmH2O | Modern gaming cases |
| Dust filter plus panel | 60-85% | 0.45-1.10 mmH2O | Front intake planning |
| Dense radiator | 45-75% | 0.80-2.50 mmH2O | Water cooling radiators |
Restriction percentages are planning estimates. A real case can be better or worse depending on clearance and turbulence.
| Rating | Fan style | Best match | Watch out for |
|---|---|---|---|
| 0.5-1.0 mmH2O | Quiet airflow fan | Open exhaust, wide mesh | Dense filters or radiators |
| 1.0-2.0 mmH2O | Balanced case fan | Filtered intake, tower coolers | Very restrictive front panels |
| 2.0-3.5 mmH2O | Pressure fan | AIO and medium radiators | Higher RPM noise |
| 3.5+ mmH2O | High speed pressure fan | Dense rads, servers, ducts | Whine and vibration control |
Static pressure is not airflow by itself. It tells you how much airflow the fan can preserve against resistance.
| CFM | m3/h | Example | Planning note |
|---|---|---|---|
| 25 | 42.5 | Small fan or restricted intake | Useful for SFF spot cooling |
| 50 | 84.9 | Common 120 mm case fan | Good single fan baseline |
| 75 | 127.4 | Strong 120 or quiet 140 | Solid GPU intake target |
| 100 | 169.9 | High airflow 140 mm | Often needs open mesh |
| 150 | 254.9 | Large fan or fan bank | Case pressure balance matters |
Multiply CFM by 1.699 to convert to cubic meters per hour.
You buy a fan to move air, but you don’t know how much it will actualy move. You don’t really know how hard that fan will push in your case. And that’s why most cooling plans fail, there is a gap between marketing spec and thermal reality. Sure, a high RPM number sounds great in a spec sheet; but what about when the fan hits the dense radiator or the dust filter? How much air does it push then?
The calculator above closes that gap. It takes into account the resistance of a real world setup, such as fans behind dust filters or fans pushing air through dense radiators. Then it estimates the installed airflow. In short, it calculates what the fan can do in theory versus what it can do in practice. What it can do in practice.
Why Fans Fail in Real Life
This misses the geometry. RPM is a meaningless number. A 1-inch diameter fan could spin at 5000 RPM and move less air then a 5-inch diameter fan ticking away at 2500 RPM. Airflow isn’t a function of RPM, it’s also a function of diameter. More air moves through bigger fans without making as much noise. Big fans accelerates larger amounts of air at slower speeds; they chop little packets fast, whereas big fans move big masses slow. When you change RPM and diameter in the tool, what you’re seeing is the balance between efficient displacement versus brute force.
People mess up here. They run after RPM because they think it means cooling. But it doesn’t necessarily mean anything except that you’ll make lots of noise. That leads us into restriction issue. Free air is what fans are rated for. This only happens on a test bench. In reality, inside of your chassis, your fan must push past dust filters, mesh grills, and often a thick radiator. All of these layers creates a demand for static pressure. If your fan can’t generate sufficient pressure to defeat that demand, its airflow will drop sharply. The tool takes this into account using derating factors based off your cooling path. A radiator with many fins per inch demands much higher pressure than a standard tower heatsink. Buying horsepower for a job your fan isn’t suited for is like putting a sports car engine on a truck; the power is there, but the drag kills the performance.
There’s also the issue of static pressure. You don’t always need high airflow when moderate static pressure works just as well. A well-balanced fan with good static pressure can keep moving at lower speeds. In contrast, a high-airflow fan may stop moving air when it is asked to do so. This is laid out in the fan chart/table on the page and details which classes of fan are best suited for various levels of restriction. Most quiet fans tend to trade off pressure for quieter operation. They are great for exhaust fans but terrible for intake fans that feed from a filter. Match your fan character to the obstacle it must push past. Need to push through a forty-five millimeter thick radiator? Get a pressure oriented blade design, not a propeller made for flow.
A subtler factor is air density; warmer air is less dense, so each revolution carries a little less mass along with it. This matters even more in server rooms than in desktop cases. However, the calculator takes this into account because that factor is present. You have to think about more than the hardware: you have to think about where that hardware sits, too. Most of us treat our computers as if they are always in standard conditions, assuming the airflow will be fine regardless of the temperature around them. It isn’t, though; a badly-ventilated closet or a hot summer day changes how much cooling your build provides.
After that, you get an estimated number of fans to reach your target as well as the actual number you have installed. So now, do I really need 4 fans? Or will 3 be fine? You should of had more fan before. It eliminates the guessing game regarding component placement and case selection. Now you’re thinking about the physics behind your setup instead of buying fans because they’re red, blue, purple, or because they’re made by XYZ.
The numbers become understandable after realizing that restriction kills flow and pressure preserves it. You no longer look for the fan with the highest RPM, but rather the one that moves air even when it has to push through tight spaces. This change in thought process makes all the difference. Faster isn’t airflow; harder is airflow. You should of known this. It would of been better to check first. Your furnitures needs care. The fan dissapears. It is luxurios.
