Select fan speed, tachometer pulse rate, or pulses per revolution, then enter the two known values. RPM/RPS and PPS/PPM conversions are supported; PPU is retained as a legacy alias meaning pulses per rotation.
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CPU Fan Speed RPM Formula
The CPU fan speed calculation uses the relationship between fan rotations and tachometer pulses. In base units, fan speed is in revolutions per minute, pulses are measured in pulses per second, and pulse count is measured in pulses per revolution.
- RPM = CPU fan speed in revolutions per minute
- PPS = pulses per second from the fan tachometer signal
- PPR = pulses per revolution, the number of tachometer pulses generated for each full fan rotation
To solve for pulses per second, the formula is rearranged:
To solve for pulses per revolution, the formula is rearranged:
Select the quantity to calculate and enter the other two values. A known positive pulse count allows zero fan speed and zero pulse rate. Inferring pulses per revolution requires positive speed and positive pulse rate; zero speed with zero pulses does not determine a unique pulse count.
The calculator also supports these unit conversions:
- RPS to RPM: multiply by 60
- RPM to RPS: divide by 60
- PPM to PPS: divide by 60
- PPS to PPM: multiply by 60
- PPU and PPR: PPU is this page’s legacy alias for pulses per rotation; it is not a distinct physical unit
Common Fan Tachometer Pulse Values
Most PC fan speed readings come from a tachometer wire. The fan sends a set number of pulses for each full rotation, and the monitoring circuit converts that pulse rate into RPM.
| Pulses per Revolution | Common Meaning | Example at 1800 RPM |
|---|---|---|
| 1 PPR | One tach pulse per fan rotation | 30 PPS |
| 2 PPR | Very common for PC cooling fans | 60 PPS |
| 4 PPR | Higher pulse-count tach signal | 120 PPS |
Illustrative CPU Fan RPM Ranges
These ranges are examples, not a cooling adequacy test. Fan model, size, airflow restriction, cooler and temperature targets determine appropriate operation; consult the manufacturer’s specifications.
| Fan Speed | Typical Situation | Notes |
|---|---|---|
| 500 to 900 RPM | Low-speed or quiet operation | Common when CPU temperature is low |
| 900 to 1800 RPM | Normal desktop use or light load | Typical for many 120 mm CPU cooler fans |
| 1800 to 3000 RPM | High load or smaller fan | Often louder, but moves more air |
| 3000+ RPM | Small, high-speed fan or aggressive cooling | More common on compact coolers and server-style fans |
Examples
Example 1: Calculate CPU fan speed from pulses per second
You measure 80 pulses per second from a fan tach signal. The fan produces 2 pulses per revolution.
The CPU fan speed is 2400 RPM.
Example 2: Calculate pulses per second from RPM
A CPU fan is running at 1500 RPM and produces 2 pulses per revolution.
The tachometer signal is 50 pulses per second.
FAQ
What does pulses per revolution mean for a CPU fan?
Pulses per revolution is the number of tachometer pulses the fan sends during one complete rotation. Many PC fans output 2 pulses per revolution, but this can vary by fan design. If your RPM result is exactly half or double what you expect, the pulses per revolution value is often the reason.
How do you convert pulses per second to RPM?
Multiply pulses per second by 60, then divide by pulses per revolution. For example, if a fan signal is 70 PPS and the fan produces 2 PPR, the speed is 2100 RPM because (70 × 60) / 2 = 2100.
Is RPM the same as RPS?
No. RPM means revolutions per minute, while RPS means revolutions per second. To convert RPS to RPM, multiply by 60. To convert RPM to RPS, divide by 60.
