Eighty decibels is ten thousand times as much sound as forty, not twice as much. The decibel scale does not add but multiplies: three decibels more is twice as much sound, ten decibels more is ten times as much. Forty decibels more is four times ten, so ten to the power four.
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Eighty decibels is not twice as much sound as forty. It is ten thousand times as much, because the decibel scale does not add but multiplies.
Loudness covers an enormous range: between the softest sound you can just about hear and a chainsaw there is a factor of a hundred billion. That does not fit on an ordinary ruler, and that is why a sound level meter measures loudness in decibels (dB). In this video you see why three decibels more is twice as much sound and ten decibels more is ten times as much. With a cooker hood on setting one (54 dB) and setting three (72 dB) you work out how many times as much sound that is: 18 dB is six doublings, so 64 times. And you see why the scale was made this way: ten times as much sound sounds to your ear about twice as loud.
For secondary school physics, in the chapter on sound. Halfway through there is a question followed by a silence: pause the video there and think for yourself first.
In this video
The full explanation, in writing
The scale that does not add
0:00Eighty decibels is not twice as much as forty. It is not ten times as much either, and not a hundred times. It is ten thousand times as much sound.
What loudness is, and why it has a scale of its own
0:16Everything that makes sound vibrates. The further that vibration goes back and forth, the more sound goes out into the room. That is the loudness. Put that in a plain number, the scale becomes useless: between the softest sound you can just about hear and a chainsaw there is a factor of billions.
0:36That is why there is a different scale. The instrument is called a sound level meter, and what comes out of it is in decibels. That scale does not add. It multiplies.
Three more, and ten more
0:48Twice as much sound is three decibels more. Not twice as many decibels: three more. Another doubling is another three more, so six. Once more, nine. Every doubling costs the same three. And ten times as much sound is ten decibels more. So twenty decibels more is ten times ten: a hundred times as much.
1:10And forty decibels more is ten thousand times. Now you. A difference of thirty decibels. How many times as much sound is in that?
The cooker hood on setting one and setting three
1:21A thousand times. Thirty decibels is three times ten decibels. The kitchen cooker hood is on setting one: fifty-four decibels. On setting three it is seventy-two. The difference is eighteen decibels. Eighteen divided by three is six doublings.
1:38Two, four, eight, sixteen, thirty-two, sixty-four. Sixty-four times as much sound comes out of that hood. If you got six, you mistook the number of doublings for the answer.
Why that scale exists at all
1:50Sixty-four times as much sound, but that is not how it sounds. It sounds more like three times as loud or so. Your ear does not add either. To make something sound twice as loud there has to be about ten times as much sound. Suddenly that scale makes sense.
2:07It was made not for calculating but for your hearing: ten decibels more is ten times as much sound, and you hear that as about twice as loud.
Summary
2:18Three things. One: you measure loudness with a sound level meter, in decibels. Two: that scale does not add but multiplies. Three decibels more is twice as much sound, ten decibels more is ten times as much. Three: to go from a difference to a factor, you divide by three.
2:36That is how many times it has doubled, and only then do you start doubling.
The two questions
2:41Two questions. First question: a sound of fifty decibels, and one of sixty decibels. How many times as much sound is in the second one? Question two: and if the difference was not ten but twelve decibels?
The answers
2:58Ten times. Ten decibels more is ten times as much sound. And for twelve: twelve divided by three is four doublings. Two, four, eight, sixteen. Sixteen times as much sound, for only two decibels more. That is how fast that scale climbs.
Closing
3:13You can now take any difference in decibels and work out how many times as much sound is in it. On the channel there is a separate video about what distance does to sound, and that works differently than you think.
Frequently asked questions
How many times as much sound is 80 dB compared with 40 dB?
Ten thousand times. The difference is 40 dB, and every 10 dB more is ten times as much sound. Four times ten times over is ten to the power four, so ten thousand.
How much more sound is 3 dB more?
Twice as much. Every doubling of the loudness is three decibels more, so 6 dB more is four times as much and 9 dB more is eight times.
A cooker hood makes 54 dB on setting one and 72 dB on setting three. How many times as much sound is that?
64 times. The difference is 72 dB minus 54 dB, which is 18 dB. Eighteen divided by three is six doublings, and two to the power six is 64. If you get six, you have mistaken the number of doublings for the answer.
Why do we use decibels and not an ordinary number for sound?
Because the range is too large for an ordinary scale: between the softest sound you can hear and a chainsaw there is a factor of about a hundred billion. On top of that, ten times as much sound sounds to your ear about twice as loud, so a scale that multiplies suits your hearing.
If you get six for the cooker hood, you have mistaken the number of doublings for the answer.
Physics with Thomas makes physics explainers for secondary school. No words on screen, so what you see works in any language.
In this series
Sound and vibrationwhat you hear is not the air from his mouth6:53
Frequency, amplitude and pitchlouder is not higher5:57
Resonance and vibrating alongit is timing, not force6:17
Fundamental, overtones and timbresame tone, other sound6:06
The tone of an air columnf = v divided by 4L3:15
Decibels and loudness80 dB is not twice 40 dB3:31
Loudness and distancetwice as far, four times quieter3:27
Anti-noisemore sound and yet quieter2:31
The ear and hearing thresholdzero decibels is not silence5:38
Hearing damage and risk thresholdno pain does not mean safe6:23
About me
My name is Thomas Schuurmans, and I have a passion for physics and for understanding why things work the way they do. What I want is to get young people asking “why is that?” and “how does that work?” more often, and to hand them the tools of physics in a way that is simple and that you can see.
I graduated in applied physics at Delft University of Technology in 2003. After that I spent more than twenty years outside education: first at TNO, the Dutch applied research institute, then at a design agency, and eventually founding Proportion Global, through which I work on innovation questions in Africa, Latin America and South Asia. That work resembles physics more than you would expect: don't start from a solution, first understand what is going on, try something, be wrong, and look again.
Since 2026 I have been teaching physics to both lower and upper secondary classes, and I started a master's at the University of Amsterdam for my full teaching qualification. That is where I learned that a secondary school pupil's real attention for new material lasts about seven minutes. And my own weakness happens to be telling too many side stories.
That is where the idea came from: videos that explain one topic sharply and visually, inside those seven minutes. I make them for my own pupils. Then I publish them, because good explanation should be within reach of anyone who needs it, wherever you live and whatever language you think and speak in.