I am buying a 7 string guitar , but i need inmediately which gauge may I put there if I want to tune it in G#??
I usually use a 7 string guitar with .12-.52 gauge.

Thanks

P.D. I´ve got 2 hours to requets him, so PLEASE tell me wich one the 7th string gauge is.

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Well, G# is only one and a half steps lower than the normal 7-string tuning, right? So, that would be like tuning a 6-stringer down to C#. For that, I'd recommend medium gauge. I actually use 11 (or 12) to 52 on my 6 string guitar which I tune to D. So, medium gauge for it (which I'm guessing would be what you just listed as 12 - 52) would be the best. Is it drop-tune to G#, or all of em down one and a half steps? Eh, what the hell. I think either way it'd work as long as it's medium and not light.
EDIT: and remember, don't forget the necessary adjustments of your truss rod. Happy trails.

you could always pick up a pack of Zakk wyldes strings. One of them has a 60 or a 70 gauge string.

pop a 70 in for the b string, that should work just fine

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.12-.15 gauge is good for detuning but you should not use any thinner strings because then the strings will lose the tone and the only thing that's left is humming.