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40 dB vs 55 dB

55 dB is 15 dB louder than 40 dB — about 32× the sound energy and roughly 2.8× the perceived loudness. In practice that is the difference between a refrigerator and a mechanical keyboard.
40 dB 55 dB 40 55
The bars show the two levels on the 0–140 dB scale. The gap looks small as a number, but on a logarithmic scale each 10 dB is a ten-fold jump in energy.
40 dB55 dB
Typical sourceA refrigeratorA mechanical keyboard
CategoryQuietModerate
Sound pressure2.0e-3 Pa0.0112 Pa
NIOSH safe timeUnlimitedUnlimited
Protection neededNoNo

Why 15 dB is a bigger jump than it looks

A 15 dB gap looks small written down, but decibels are logarithmic. Every 10 dB multiplies sound energy by ten and roughly doubles perceived loudness. Going from 40 dB to 55 dB therefore multiplies the acoustic energy by about 32× while your ear reports something closer to 2.8× as loud. Both statements are true — they simply measure different things.

Which one is safe?

Both 40 dB and 55 dB fall below the 85 dBA action level, so neither carries a hearing-damage risk at any duration. The practical difference is annoyance and speech interference rather than safety.

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The distance equivalent

One intuitive way to feel a 15 dB difference is to think in distance. Outdoors, every doubling of distance removes about 6 dB, so standing at 55 dB versus 40 dB is roughly like standing 5.6× closer to the same source. Conversely, moving about 5.6× further away would bring 55 dB down to 40 dB.

Adding the two levels together

Decibels do not add arithmetically. A 40 dB source running alongside a 55 dB source does not produce 95 dB — the correct total is 55.1 dB, calculated as 10 × log₁₀(10^(40/10) + 10^(55/10)). Because the louder source dominates, the quieter one contributes only 0.1 dB. Our decibel calculator does this for any combination.

Frequently asked questions

Is 55 dB much louder than 40 dB?
55 dB carries about 32 times the sound energy of 40 dB and is perceived as roughly 2.83 times as loud.
What is the difference between 40 dB and 55 dB?
The difference is 15 dB. 40 dB is comparable to a refrigerator, while 55 dB is comparable to a mechanical keyboard.
What do 40 dB and 55 dB add up to?
Combined, two sources at 40 dB and 55 dB produce about 55.1 dB — not 95 dB — because decibels add logarithmically.
Which is safe, 40 dB or 55 dB?
Both are below the 85 dBA action level and safe for unlimited exposure.

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Sources & accuracy. Reference levels are drawn from published data by NIOSH, OSHA, the CDC, the WHO Environmental Noise Guidelines and the American Speech-Language-Hearing Association (ASHA). Real-world readings vary with distance, room acoustics and the specific source, so treat every figure as a typical value rather than an exact constant. Last reviewed 2026-08-11.