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55 dB vs 75 dB

75 dB is 20 dB louder than 55 dB — about 100× the sound energy and roughly 4.0× the perceived loudness. In practice that is the difference between a mechanical keyboard and a toilet flushing.

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.

	55 dB	75 dB
Typical source	A mechanical keyboard	A toilet flushing
Category	Moderate	Loud
Sound pressure	0.0112 Pa	0.1125 Pa
NIOSH safe time	Unlimited	Unlimited
Protection needed	No	No

Why 20 dB is a bigger jump than it looks

A 20 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 55 dB to 75 dB therefore multiplies the acoustic energy by about 100× while your ear reports something closer to 4.0× as loud. Both statements are true — they simply measure different things.

Which one is safe?

Both 55 dB and 75 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 20 dB difference is to think in distance. Outdoors, every doubling of distance removes about 6 dB, so standing at 75 dB versus 55 dB is roughly like standing 10.0× closer to the same source. Conversely, moving about 10.0× further away would bring 75 dB down to 55 dB.

Adding the two levels together

Decibels do not add arithmetically. A 55 dB source running alongside a 75 dB source does not produce 130 dB — the correct total is 75.0 dB, calculated as 10 × log₁₀(10^(55/10) + 10^(75/10)). Because the louder source dominates, the quieter one contributes only 0.0 dB. Our decibel calculator does this for any combination.

Frequently asked questions

Is 75 dB much louder than 55 dB?

75 dB carries about 100 times the sound energy of 55 dB and is perceived as roughly 4.00 times as loud.

What is the difference between 55 dB and 75 dB?

The difference is 20 dB. 55 dB is comparable to a mechanical keyboard, while 75 dB is comparable to a toilet flushing.

What do 55 dB and 75 dB add up to?

Combined, two sources at 55 dB and 75 dB produce about 75.0 dB — not 130 dB — because decibels add logarithmically.

Which is safe, 55 dB or 75 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.