What is Bit Depth?
Also called: word length, resolution
Bit depth is the number of bits used to store each audio sample, which sets how precisely the level of the sound wave is recorded. Common bit depths are 16 bit, 24 bit and 32 bit float.
Each extra bit adds about 6 dB of theoretical dynamic range between the noise floor and the loudest possible level. That gives 16 bit audio about 96 dB and 24 bit audio about 144 dB, more than any real microphone or converter can deliver.
24 bit is the usual choice for recording and mixing because it leaves plenty of room above the noise, so levels do not need to be pushed close to clipping. 32 bit float files cannot clip inside the file, which makes them handy for exports between programs.
16 bit is the CD standard and is enough for listening. When reducing the bit depth for a final file, dithering should be applied.
Put it to work
Calculate how big a file will be at different bit depths and sample rates.
Audio File Size and Bitrate Calculator