How loud was Krakatoa?
The climactic explosion of Krakatoa on 27 August 1883 is usually put at about 172 dB at roughly 100 miles (160 km), the conversion Nautilus makes from a pressure spike of over 2.5 inches of mercury on a gauge at the Batavia gasworks. No sound level meter existed; the number is derived from a pressure record, and the gauge went off its scale. Guinness World Records lists Krakatoa as the loudest noise ever recorded, heard 5,000 km away.
- Level
- 172 dB peakunweighted peak sound pressure level
- Daily limit
- No safe unprotected exposureimpulse noise
What the numbers mean
How it was measured. Not a sound level meter reading. The figure is a conversion of a pressure spike on the Batavia gasworks gauge into decibels re 20 µPa, unweighted. The gauge trace went off the top of its chart, and published readings of that spike differ (see body).
Nobody measured Krakatoa in decibels. What survives is a pressure trace from the gasometer indicator at the Batavia gasworks, which the Royal Society's 1888 report reproduces as Plate IX. The report says the gauge showed "a sudden and most extraordinary increase of pressure" between about 10:15 and 10:20 local time, and that on the original the trace "passes beyond the limits of the diagram", so the true peak is unknown. The report gives the distance from Batavia to Krakatoa as 83 miles in a straight line; popular accounts round this to 100 miles.
The 172 dB figure comes from Aatish Bhatia's 2014 Nautilus article, which says the Batavia gauge registered a spike of over 2.5 inches of mercury and converts that to over 172 decibels. Treat it with care. The Royal Society's own table of the Batavia air waves lists the 10:15 reading as 63 mm of water above normal, with a barometric equivalent of 0.37 inches of mercury, far less than 2.5 inches, although that reading is itself a lower bound because the pen hit the edge of the chart. So the order of magnitude is clear (an extraordinarily loud blast over a hundred miles away) but the exact decibel figure depends on which reading you use.
Other evidence of the loudness is more direct. The captain of the Norham Castle, about 40 miles away, wrote that the eardrums of over half his crew had been shattered. The explosion was heard about 3,000 miles away on Rodrigues, near Mauritius, where it sounded like distant heavy guns; Guinness World Records gives 5,000 km. Close to the volcano the pressure swing would have exceeded the roughly 194 dB limit at which air can carry an undistorted sound wave, making it a shock wave rather than ordinary sound.
The 2022 Hunga Tonga-Hunga Ha'apai eruption is the only modern comparison. A study in Science found that, measured by the amplitude of its atmospheric Lamb wave, the Hunga explosion was comparable in size to Krakatau, and that it produced audible sound at a range of about 10,000 km.
How dangerous is a 172 dB peak?
A peak of 172 dB is at or above 140 dB, the impulse limit used by NIOSH and OSHA and the EU and UK exposure limit value. A single exposure at close range can damage hearing.
| Rule | Peak limit | This sound |
|---|---|---|
| UK and EU lower exposure action value | 135 dB(C) | Above |
| UK and EU upper exposure action value | 137 dB(C) | Above |
| UK and EU exposure limit value; NIOSH and OSHA impulse ceiling | 140 dB | Above |
Protecting your hearing
Not a hazard you can plan for with hearing protection. Sailors 40 miles away suffered ruptured eardrums, so at that scale the only protection is distance and following official volcano evacuation orders.
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.
Questions
Was Krakatoa the loudest sound ever?
It is the loudest sound in recorded history. Guinness World Records lists it as the loudest noise ever recorded, heard 5,000 km away. The often-quoted 172 dB at about 100 miles is a conversion from a gas-gauge pressure reading, not a direct measurement.
How far away was Krakatoa heard?
About 3,000 miles (Guinness World Records says 5,000 km), on the island of Rodrigues near Mauritius, roughly four hours after the explosion.
How was Krakatoa's loudness measured?
By a pressure gauge on a gasometer at the Batavia gasworks, 83 miles away in a straight line. Its trace went off the chart, so every decibel figure for Krakatoa is an estimate from that record.
Sources
- The Sound So Loud That It Circled the Earth Four Times, Nautilus (Aatish Bhatia, 2014). Supports: Gauge reading of over 2.5 inHg at about 100 miles (secondary account).
A barometer at the Batavia gasworks (100 miles away from Krakatoa) registered the ensuing spike in pressure at over 2.5 inches of mercury
Checked 2026-11-02. - The Sound So Loud That It Circled the Earth Four Times, Nautilus (Aatish Bhatia, 2014). Supports: dB_low/dB_high: 172 dB at 100 miles (derived).
The Krakatoa explosion registered 172 decibels at 100 miles from the source
Checked 2026-11-02. - The Eruption of Krakatoa, and Subsequent Phenomena (Report of the Krakatoa Committee of the Royal Society, 1888), Royal Society / Internet Archive. Supports: Primary record: the Batavia gauge trace went off scale at the great explosion.
On the original the trace at about 10 hrs. 15 mins. passes beyond the limits of the diagram
Checked 2026-11-02. - The Eruption of Krakatoa, and Subsequent Phenomena (Report of the Krakatoa Committee of the Royal Society, 1888), Royal Society / Internet Archive. Supports: Primary record of the pressure spike.
The gasometer shows a sudden and most extraordinary increase of pressure
Checked 2026-11-02. - The Eruption of Krakatoa, and Subsequent Phenomena (Report of the Krakatoa Committee of the Royal Society, 1888), Royal Society / Internet Archive. Supports: Distance: 83 miles straight line.
Batavia is distant 83 miles in a straight line from Krakatoa
Checked 2026-11-02. - The Eruption of Krakatoa, and Subsequent Phenomena (Report of the Krakatoa Committee of the Royal Society, 1888), Royal Society / Internet Archive. Supports: Table of Batavia gauge readings (10:15 reading listed as 63 mm water, 0.37 in barometric equivalent; see page 95 of the report).
The second column gives the measure of the force of the air waves as registered by the pressure gauge
Checked 2026-11-02. - Loudest noise, Guinness World Records. Supports: Record listing; heard 5,000 km away.
The sound was heard 5,000 km (3,100 miles) away
Checked 2026-11-02. - Atmospheric waves and global seismoacoustic observations of the January 2022 Hunga eruption, Tonga, Science (Matoza et al., 2022) via PubMed. Supports: Hunga Tonga comparison; audible at about 10,000 km.
As measured by the Lamb wave amplitudes, the climactic Hunga explosion was comparable in size to that of the 1883 Krakatau eruption
Checked 2026-11-02.
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.