I specifically purchase noise cancelling headphones / earbuds now since it makes it easy to listen at MUCH quieter levels. I have done some tests with the noise cancelling disabled and setting the volume and with it on.. It really makes a huge difference as I am not cranking it up to drowned out noise on transit or walking down the street.

11, obviously!

WHAT? SORRY I CANT HEAR ANYMORE

I try to target under 70db to protect my ears. Some earbuds and DAC's can show you a db estimate

Sound engineer here. Please protect your ears people, there’s no way to reverse hearing damage.

depends.

In the middle of angry-programming? The linkin park will be turned up to 80%. I want to make sure Chester's screams wakes the dead.

Business as usual? around 20%. Enough to drown out external noises.

I use the headphone safety feature of my phone to limit it to 80dB. Anything higher and you’re risking permanent hearing loss.

Guide.

11

As quietly as possible, you don't notice hearing damage until it's too late to do anything about it.

10-15% on earphones. However, that doesn't really mean anything. Different sound card and headphone combination will produce different loudness at same levels.

I'm just going to take this moment to remind everyone not to destroy their hearing. Back in highschool I used to blast my ears with headphones at maximum volume and go to loud venues without hearing protection. I've been permanently listening to EEEEEEEEEEEEE ever since. That was 25 years ago. It never goes away folks. Stay safe!

20% typically. I prefer to be able to hear my surroundings clearly still

I listen at a low volume. I'm usually doing something else as well, so loud music is too distracting and irritating. I'm old, and I can still hear very well except for spousal deafness.

I love that the font size on this post is twice as big as all the others.

multiples of 5

Some very arbitrary answers up in here

on speakers? reasonable minus a notch or two

on headphones? cranked

20-40% when I'm at home and there are no noises that interrupt the sound. 50-75% when I'm outside and can't hear anything on lower levels. I try to keep this stuff as quiet as possible so as not to damage my hearing

Depends. My IEMs have higher impedance than your usual pair of headphones, and then it also depends on what I'm listening to from my self-ripped .flac library. Right now I am listening to Savage Amusement by Scorpions and I can listen to it enjoyably at 65 out of 120 on my Walkman. The Dark Side of the Moon by Pink Floyd is a tad bit quieter so on that album I have 75. Usually it's around this volume range, but sometimes if it's a raw grimey death metal album I have to go even higher.

tl;dr:

It mostly depends on how loud or quiet the album I'm listening to is.

I primarily listen to music in my car and it’s usually as loud as I can stand.

With headphones and speakers it is always as quietly as possible since I already have ear damage, I don't want more.

WHAT?

Jokes aside, just over 50% system volume in general with apps and headphones maxed out. My hearing is so/so. I wish it were below 50 but it's just too quiet like that

60%

I use Reduce Loud Sounds on the iPhone with my AirPods Pro to reduce the maximum volume to 80dB so that I don’t damage my hearing. That way, I can crank the volume buttons to maximum without having to think about it, knowing that it will be safe.

Full on speakers, around 50% to 80% on IEMs/headphones; depends on the max volume I can do without getting tinnitus.

WHAT?

For short car journeys or if I'm sharing, quietish background level

If I'm motorwaying it alone, fairly (but not stupidly) loud