Dear Friend,
Here is a chart I have made for your reference.  If you become familiar with these numbers and are conscientious about proper humidity for your instrument, your guitar will remain in pristine condition through many, many years. 

The figures below represent RH (Relative Humidity):

100%; You shouldn’t really be playing your new guitar out in the rain
 
95%; This is dangerous for your instrument; glue joints are compromising right now and the thin wood plates are highly stressed and buckling due to their swollen condition 

90%; This is far too humid for your instrument; the action of the strings is very high; maybe it’s time for some air conditioning for both of you? Bad things are possibly going to start happening to your instrument 
 
85%; Too humid; your wood plates are beginning to swell with the moisture; this isn’t good 

80%; A little too humid I think (plus, aren’t you getting uncomfortable?); soundboard movement is starting to affect the action (making it higher over the frets) 

75%; Probably getting too humid; if it keeps up you may actually notice the soundboard movement; sort of OK for awhile 

70%; OK for awhile but don’t let the guitar get too warm; more wood movement with the soundboard bellying out somewhat perhaps 
 
65%; A little too humid; there might be a small bit of wood movement but don’t panic
 
60%; Still sort of OK
 
55%; Not too bad
 
50%; OK  

45%; PERFECT 

40%; OK 

35%; Time to think about humidifying your guitar; the soundboard is starting to sink in; probably will be OK for a few days so don’t panic (yet!)
 
30%; It is really time for humidifying your guitar, (a few days might be ok); action starting to get low; maybe you can start to feel the ends of the frets beyond the edge of the fretboard (which has shrunk back due to moisture loss); install the Planet Waves Guitar Humidifier when you are not playing the instrument
 
25%; Time to be really concerned; time is not on your side; take corrective action now; use the Planet Waves Guitar Humidifier and put the guitar in the case until the dry conditions are over; cracks are planning their assault; frets are hanging over the edge of the fretboard now
 
20%; Danger Will Robinson!!! You are living on the edge now; huge stresses are building up in the plates of your expensive instrument and; cracks may start to appear at any moment; the soundboard is sunk in and you have string buzzes
 
15%; Give me a call and we can discuss a time slot for your repair
 
10%; Now we need more time to fix all those cracks and glue the thing back together
 
5%;   It’s over!