NTSC has a nominal resolution of 720x480i (240 lines per field, 60 fields per second). VHS on its best days could get about half the horizontal resolution for luma, and even less for color, but often ended up a bit worse, so 320x480i is probably a good approximation for the resolution (ignoring the fact that color is even lower resolution).
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On a slightly different note, the HiFi audio track (supported for playback by pretty much all VCRs by the late 80s; not sure if/when HiFi recording became normal) of VHS was undoubtably the highest quality consumer analog audio product to get wide usage, with an SNR and dynamic range slightly better than the very best cassette decks.
[edit]
On a slightly different note, the HiFi audio track (supported for playback by pretty much all VCRs by the late 80s; not sure if/when HiFi recording became normal) of VHS was undoubtably the highest quality consumer analog audio product to get wide usage, with an SNR and dynamic range slightly better than the very best cassette decks.