How loud is a car horn?
Under UN Regulation No. 28, a car's horn must produce at least 93 dB(A) measured 7 m in front of the vehicle. The horn unit itself must produce between 105 and 118 dB(A) at 2 m in a laboratory-style test.
- Level
- 93–118 dBA maxA-weighted maximum sound level
- Daily limit
- 14 s a dayNIOSH, at the loud end
- Versus conversation
- 19,953× energyabout 19.7× as loud
What the numbers mean
How it was measured. UN Regulation No. 28 as originally adopted (1973): a horn fitted to a vehicle must give at least 93 dB(A) at 7 m in front; the horn unit itself must give 105 to 118 dB(A) at 2 m on a test rig. Later amendments to the regulation were not checked.
UN Regulation No. 28 covers the approval of horns and of vehicles with regard to their audible signals. On a test rig, with the microphone 2 metres from the horn's sound outlet, the A-weighted level must be at least 105 dB(A) and no greater than 118 dB(A). Once the horn is fitted, the level measured 7 m in front of the vehicle, with the engine off, must be no less than 93 dB(A).
The gap between the two figures reflects the extra distance and the way the horn is mounted behind the bumper or grille. Someone standing right beside the bonnet hears more than the 7 m figure. These numbers come from the regulation as it entered into force in 1973.
How long is safe?
NIOSH recommends no more than 14 s a day at 118 dBA (1 h 16 min at 93). OSHA's legal limit is 9 min 54 s. This is a maximum, so a time limit based on it is a worst case.
| Level | NIOSH limit (85 dBA, 3 dB rule) | OSHA limit (90 dBA, 5 dB rule) | UK/EU 80 dB(A) action value reached after | UK/EU 85 dB(A) action value reached after |
|---|---|---|---|---|
| 93 dBA | 1 h 16 min | 5 h 17 min | 24 min | 1 h 16 min |
| 118 dBA | 14 s | 9 min 54 s | 5 s | 14 s |
Times are for a whole day’s exposure, with the rest of the day quiet. The workplace limits were written for adults at work, not for children. Work out a mixed day with the noise dose calculator.
Protecting your hearing
Use the horn briefly and only when needed. If a horn sticks on in a confined space such as a garage, disconnect it rather than standing next to it.
Earplug and earmuff ratings (NRR in the US, SNR in the UK and EU) are lab figures; real-world protection is usually lower. How to read the ratings.
Compared with sounds nearby
Using midpoints of each range. Energy multiplies by 10 every 10 dB; perceived loudness roughly doubles (why).
- Train horn (96–110 dBA): this has about 1.8× its sound energy and sounds about 1.2× as loud.
- Nightclub (94–112.4 dBA): this has about 1.7× its sound energy and sounds about 1.2× as loud.
- MRI scanner (102–115.8 dBA): it has about 2.2× the sound energy of this and sounds about 1.3× as loud.
- Crying baby (99–120 dBA max): it has about 2.5× the sound energy of this and sounds about 1.3× as loud.
- Normal conversation (55–70 dBA): this has about 19,953× its energy and sounds about 19.7× as loud.
Questions
How loud is a car horn?
UN rules require at least 93 dB(A) at 7 m in front of the vehicle; the horn itself must give 105 to 118 dB(A) at 2 m on a test rig.
Is there a maximum loudness for car horns?
For the horn unit, yes: no more than 118 dB(A) at 2 m under UN Regulation No. 28.
Sources
- Regulation No. 28: Uniform provisions for the approval of audible warning devices and of motor vehicles with regard to their audible signals (United Nations Treaty Series, Volume 854), United Nations. Supports: dB_low 93 dB(A) fitted to vehicle.
The maximum value observed must not be less than 93 dB (A).
Checked 2026-11-03. - Regulation No. 28: Uniform provisions for the approval of audible warning devices and of motor vehicles with regard to their audible signals (United Nations Treaty Series, Volume 854), United Nations. Supports: 7 m measurement position.
distance of 7 m in front of the vehicle
Checked 2026-11-03. - Regulation No. 28: Uniform provisions for the approval of audible warning devices and of motor vehicles with regard to their audible signals (United Nations Treaty Series, Volume 854), United Nations. Supports: 105 to 118 dB(A) horn unit; dB_high 118.
shall be at least 105 dB (A) and not greater than 118 dB (A)
Checked 2026-11-03. - Regulation No. 28: Uniform provisions for the approval of audible warning devices and of motor vehicles with regard to their audible signals (United Nations Treaty Series, Volume 854), United Nations. Supports: 2 m bench distance.
diaphragm of the microphone and the sound outlet of the device shall be 2 metres
Checked 2026-11-03.
This page is general information, not medical advice. If you have ringing in your ears, muffled hearing or any change in your hearing, see an audiologist or your doctor.