How Much Noise Disturbs Sleep? The Decibel Thresholds

Three sets of WHO guidance matter, and they draw the lines at different points in the chain.

Inside the bedroom: the WHO's community noise guidance recommends keeping continuous background noise in the bedroom below about 30 dB, and single noise events below about 45 dB at the ear, to protect sleep. Those two numbers - the steady floor and the event peak - are the pair worth remembering, because they map directly onto the two ways a bedroom gets noisy.

Outside the window: the 2009 Night Noise Guidelines for Europe set a target of 40 dB for average night-time noise outside the facade, after reviewing evidence that effects on sleep begin to appear once outside levels pass about 30 dB. A closed window drops roughly 10 to 15 dB off what reaches the pillow, and an open one much less, which is how the outside and inside numbers connect.

By source: the 2018 guidelines went further and set night limits per source - around 45 dB for road traffic, 44 dB for railway and 40 dB for aircraft noise, averaged across the night outside the dwelling. Aircraft get the strictest line because each overflight is a distinct event with a sharp rise, and events are what wake people.

Two cautions when using reference tables like this. Decibels are logarithmic: a 10 dB increase is roughly a doubling of perceived loudness, so the step from 40 to 50 dB is much bigger than it reads. And a phone's sound-meter app measures the room, not the ear - it cannot see through your pillow, your bedding or the wax in the app's calibration, so treat phone readings as rough guides rather than measurements.

The sleeping brain does not switch hearing off. It keeps monitoring, and what it reacts to is change: a sound that protrudes above the background, especially one with a fast rise, like a door slam, a motorbike pulling away or a fox scream. A steady 45 dB of motorway rumble is genuinely easier to sleep through than a quiet street punctuated by 55 dB events, because the rumble contains no change to react to and the brain habituates to it within nights.

Meaning cuts through too. The sleeping brain privileges sounds that carry information - your own name, your baby, a phone alert tone you have trained yourself on - and rouses to them at lower levels than to meaningless sound. It is why parents sleep through storms and wake to a cough, and why the neighbour's muffled conversation can disturb you more than louder, blanker noise: speech is the most information-dense sound there is.

So the disturbance ranking of a bedroom is set less by its average level than by its event profile: how often sounds protrude above the floor, how sharply they rise, and whether they carry meaning.

Yes, and this is the finding that makes night noise a public-health issue rather than an annoyance. Waking you fully is only the top rung of a ladder of responses, and the lower rungs fire at lower volumes.

Noise events too quiet to wake you still trigger partial arousals: brief shifts from deeper sleep toward lighter sleep, visible on an EEG (a recording of the brain's electrical activity) but gone from memory by morning. They also fire the body's alerting machinery - heart rate and blood pressure rise transiently with noise events during sleep, without any conscious waking. Traffic-noise research has documented these autonomic responses at event levels well below the waking threshold, and the association between long-term night noise and cardiovascular risk is a large part of why the health effects of noise are taken seriously by regulators.

The practical consequence: you cannot audit your bedroom by recall. A night you remember as unbroken can still have been fragmented by dozens of arousals, and the morning-after evidence is indirect - waking unrefreshed after enough hours, grogginess that outlasts the first coffee. If the room is noisy and your mornings are heavy, the noise is a suspect even if you never hear it.

Before fixing anything, spend two nights profiling the room, because the fix depends on the profile rather than the loudness. Lie down at bedtime and again if you wake in the small hours, and separate what you hear into the floor - the steady layer that never stops, like distant traffic or a fridge through the wall - and the events that protrude from it. Note the events by hour: bins and deliveries cluster before 7am, boilers fire on timers, birdsong arrives with first light, and a neighbour's routine repeats to the minute. A phone sound-meter app is a fair way to put rough numbers on the floor, less useful for catching two-second events.

Then sort the events by how they travel. Airborne noise - voices, traffic, music - comes through the window and responds well to closing it, to masking and to earplugs. Structure-borne noise - footsteps overhead, doors, plumbing - arrives through the building itself, sails past a closed window, and masks poorly because it protrudes so sharply; for that class, dampening at the source or a conversation upstairs beats anything you can do inside the bedroom. Ten minutes of honest profiling routinely redirects the whole plan.

Everything above points at one mechanism: sleep is disturbed by sounds that protrude above the background. That gives you exactly two honest fixes, and they work from opposite ends.

Masking raises the floor. A fan or white noise machine adds steady, meaningless sound, so the doorbell, the neighbour's landing light switch and the 5am delivery van no longer protrude as far above the background. The events still happen; they just stop being events acoustically. Masking is the right tool for intermittent noise in an otherwise quiet room - the classic noisy-neighbours and urban-street cases.

Blocking lowers the ceiling. Earplugs cut the absolute level reaching the eardrum, typically by 20 to 30 dB when seated properly. Blocking is the right tool when the problem is loud rather than intermittent - a snoring partner, a main road with the window open - or when you cannot add sound because someone else shares the room.

The two combine well: plugs to drop the whole scene, masking to smooth what remains. Our white noise vs earplugs guide walks through choosing between them case by case, and the noisy-neighbours guide covers the masking route in detail. Whichever you choose, the WHO numbers give you the target: a steady floor the brain can habituate to, with as few protruding events as possible.