How many hours of high quality music fits on a 16 gigabyte iPod

It depends on the bitrate used to encode it; at 256Kbps, about 18.

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A "16Gb" iPod nano has enough room to store about 14.5Gb of music, assuming this to be the only media stored there. If by "high quality" you mean lossless, using Apple Lossless/ALAC format, that equates to around 30 hours of music (there will be some variations depending on the nature of the music and the degree to which ALAC compresses the audio data). AIFF files are larger, though of the same quality as ALAC - maximum in this case is approx. 20 hours.

For "iTunes Plus" quality (256kbps lossy compression) files will be between one-third and one-quarter the size of the same music in ALAC, so the total time goes up to around 90-120 hours. My 16Gb 7th gen nano is currently full to capacity using a mix of 256kbps AAC and 320kbps MP3 files - iTunes reports the total time as 4.9 days (117 hours).