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100 dB vs 120 dB

120 dB is 20 dB louder than 100 dB — about 100× the sound energy and roughly 4.0× the perceived loudness. In practice that is the difference between a jackhammer at 15 m and an ambulance siren at 1 m.
100 dB 120 dB 100 120
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.
100 dB120 dB
Typical sourceA jackhammer at 15 mAn ambulance siren at 1 m
CategoryExtremely loudDangerous
Sound pressure2.0000 Pa20.0000 Pa
NIOSH safe time15 min8.9 sec
Protection neededYesYes

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 100 dB to 120 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 levels are at or above the 85 dBA action level, so both need exposure limits. At 120 dB the safe unprotected window is only about 8.9 sec.

Hearing protection

For anything above 85 dB, rated protection matters. Look at the NRR (US) or SNR (EU) figure — real-world reduction is roughly (NRR − 7) ÷ 2.

Electronic ear muffs (NRR 22–25)Shooting, mowing — amplify speech, block bangsLink coming soon
Reusable filtered earplugs (NRR 20)Concerts & musicians — flat attenuationLink coming soon
Foam earplugs (NRR 32)Sleep, travel, DIY — highest raw NRRLink coming soon

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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 120 dB versus 100 dB is roughly like standing 10.0× closer to the same source. Conversely, moving about 10.0× further away would bring 120 dB down to 100 dB.

Adding the two levels together

Decibels do not add arithmetically. A 100 dB source running alongside a 120 dB source does not produce 220 dB — the correct total is 120.0 dB, calculated as 10 × log₁₀(10^(100/10) + 10^(120/10)). 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 120 dB much louder than 100 dB?
120 dB carries about 100 times the sound energy of 100 dB and is perceived as roughly 4.00 times as loud.
What is the difference between 100 dB and 120 dB?
The difference is 20 dB. 100 dB is comparable to a jackhammer at 15 m, while 120 dB is comparable to an ambulance siren at 1 m.
What do 100 dB and 120 dB add up to?
Combined, two sources at 100 dB and 120 dB produce about 120.0 dB — not 220 dB — because decibels add logarithmically.
Which is safe, 100 dB or 120 dB?
Both exceed the 85 dBA action level, so both need exposure limits and, ideally, hearing protection.

See each level in detail

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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.