Decibel Levels Explained: What dB Figures Mean for Your Hearing and Your Home

Decibel figures appear in every noise survey and glazing specification, but the scale is widely misunderstood. A window "reducing noise by 40 dB" is not a 40% improvement — it is something far more dramatic. This guide explains how the scale works, what common levels sound like, and which numbers matter for your hearing and your sleep.

Why the decibel scale is logarithmic

The decibel scale compresses an enormous range of sound energy into manageable numbers. Two rules of thumb are worth memorising:

• +10 dB sounds roughly twice as loud. A 70 dB street sounds about twice as loud as 60 dB.
• −10 dB sounds roughly half as loud. A 20 dB reduction feels around four times quieter; a 30 dB reduction around eight times.

This is why a specialist acoustic reduction of 40–54dB transforms a room rather than merely improving it.

What common dB levels sound like

• 30 dB — a quiet bedroom at night; the WHO-inspired target for restful sleep.
• 40 dB — a quiet library or a residential street heard through good glazing.
• 50 dB — moderate rainfall, a quiet office.
• 60 dB — normal conversation at one metre.
• 70 dB — a busy London high street; a vacuum cleaner.
• 80 dB — heavy traffic at the kerbside; a typical main-road façade.
• 90 dB — a lorry passing close by; an underground platform as a train arrives.

Our noise FAQs page includes the same scale alongside answers about how glazing changes these figures indoors.

Safe levels for hearing

Hearing damage is governed by dose: level plus duration. Workplace guidance treats 85 dB over 8 hours as the point where protection becomes necessary, and every 3 dB above that halves the safe exposure time. Everyday home noise in London rarely reaches damaging levels — the issue at home is comfort, sleep and long-term stress rather than hearing loss.

Levels that matter indoors

For homes, the health-based benchmarks are different from workplace limits:

• Bedrooms at night: around 30 dB(A) supports good sleep quality.
• Living areas in the day: mid-30s to 40 dB(A) supports concentration and conversation.
• Outside the façade at night: WHO guidance flags road-traffic noise above 45 dB Lnight as associated with sleep effects.

How much reduction do you need?

Subtract, don't divide. If your bedroom sits at 55 dB at night and the target is 30–35 dB, you need roughly 20–25 dB of improvement through the window. A standard double-glazed unit might deliver 25–30 dB of total insulation; a deep secondary glazing system with 10.8mm acoustic laminate glass can reduce external noise by up to 54dB in suitable configurations. A sound survey measures your actual starting point so the specification matches the gap you need to close.