This is generally considered the baseline or "standard" quality for digital audio. While highly optimized for saving storage space, it is a lossy format.
Are you trying to calculate the for a specific device? 128kbps mp3(2.47 MB)
Critical listeners or those using high-end headphones may notice a loss of crispness in the high-frequency ranges (like cymbals or heavy percussion) compared to higher bitrates like 320 kbps. This is generally considered the baseline or "standard"