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As gf has said, there's no one answer, simply because the figure varies, due to a whole variety of local factors e.g. obstacles/terrain near the approach path, the type of runway/approach lighting used at the airport.
Can't remember the details or where the definitive numbers are - probably a mix from Annex 10 and Doc 8168 - but there are 'system minima' for each type of approach. The system minima are the lowest OCH/DH and visibility values that can be used with that particular equipment system assuming that there no other constraints because of the things wiggy mentions (and I think you can add crew training and currency to the list in the case of precision approaches).
