How loud is a 120 mm case fan?
An independent reference on case-fan loudness, sizing and replacement, assembled from published specifications and standard measurement practice.
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Quiet models measure 18–25 dBA at 600–1,200 RPM; fast models reach 30–40 dBA above 2,000 RPM.
Put those figures against everyday anchors. The threshold of hearing is 0 dBA, a quiet room at night sits near 30 dBA and normal conversation is about 60 dBA. A quiet 120 mm fan at low speed is therefore quieter than the room it stands in, while a performance model at full speed is clearly audible at a desk but still well below conversation level.
The catch is that decibels are logarithmic. Each 10 dBA step sounds roughly twice as loud, so the jump from 20 dBA to 40 dBA is about four times the perceived loudness, not twice the number. Two fans whose specs differ by only 6–8 dBA can sound plainly different in the same case.
Speed is the lever that moves one fan between these bands. A 120 mm model that is nearly silent at 700 RPM can pass 30 dBA when a motherboard pushes it past 2,000 RPM, which is why speed control matters as much as the fan itself.
A dBA rating is a single-number snapshot, not a guarantee of how a fan will sound once screwed into a case.
Manufacturers quote one dBA figure, usually measured at maximum speed in open air. In a real build the number shifts: a fan bolted hard to a thin panel can hum through the whole chassis, while the same fan on soft mounts can drop back toward its spec-sheet figure.
Bearing type shapes the character of the noise over time. A sleeve bearing near the end of its 30,000–40,000-hour rating often rattles before it fails; rifle and hydrodynamic designs are rated around 50,000–70,000 hours, and ball bearings around 60,000–75,000 hours, both tending to keep a steadier tone.
Used honestly, the dBA figure is still the best comparison tool: lower is quieter, a 3 dBA gap is subtle, and a 10 dBA gap is a clear halving or doubling of what you hear.
| Specification | Typical figure | What it means in practice |
|---|---|---|
| Noise at low speed | 18–25 dBA at 600–1,200 RPM | Quieter than a quiet room at night (~30 dBA) |
| Noise at full speed | 30–40 dBA at 2,000+ RPM | Clearly audible, still below conversation (60 dBA) |
| Airflow | 30–70 CFM (51–119 m³/h) | Covers one intake or exhaust position |
| Static pressure | 1.5–3.0 mmH₂O (≈15–29 Pa) | Pressure-oriented models for radiators and filters |
| Mounting holes | 105 mm apart | Fits any standard 120 mm case position |
| Control signal | 25 kHz PWM, 4-pin | 100% duty cycle equals full speed |
| Power draw | ≈1.8 W (0.15 A at 12 V) | A negligible load on any modern power supply |
Frame size tells you the space a fan occupies; hole spacing tells you whether it will actually bolt on.
Standard case-fan frames are 80 × 80 × 25 mm, 92 × 92 × 25 mm, 120 × 120 × 25 mm and 140 × 140 × 25 mm. The mounting holes sit on a smaller square than the frame: 71.5 mm apart on an 80 mm fan, 105 mm on a 120 mm fan, and 124.5 mm — 130 mm on some models — on a 140 mm fan.
Airflow scales with size. A 120 mm fan commonly moves 30–70 CFM (about 51–119 m³/h), while a 140 mm fan moves 50–100 CFM, so a larger, slower fan can match a smaller one's cooling at lower noise.
The list below names the specification families and measurement conventions behind the numbers on this page.