Are dB meters on smartphones accurate?

All about the mic isn't  it? calibration? Your finger half way over the speaker, position, you know all the stuff you have to do if your interested in the data being accurate and in turn more useful. 

If you just want to know how loud it is. It will give you an idea about SPLs though, how accurate? good question..

Regards

You can get a calibrated mic for a smartphone  for about $22:


https://amzn.to/2LBaQKY

You need an app like AudioTools which accepts a calibration file.

Best,

E

depends on what you're trying to do.  Just a general idea of sound levels in your listening space?...then yes, they get you there within a dB or so.  Are you seeking workplace exposure compliance under OSHA?  Then no, you need a proper noise dosimeter that meets American National Standards Institute (ANSI) Standard S1.4-1971 (R1976) or S1.4-1983, "Specifications for Sound Level Meters."

The "SPLnFFT"  app is pretty good for the iOS platform