LJ, in theory, 1-6 reps build strength without size (hypertrophy), 8-12 reps is hypertrophic, and 13+ reps builds muscular endurance. 7 is the orphaned rep number no-one claims.
However, powerlifters and Olympic-style weightlifters do mostly low reps and they are often quite large. Rippetoe's
Starting Strength programme is based entirely on 5-rep work sets, and
he claims gains of around 30lbs (14kg) of lean mass (mostly muscle, some bone) in the first 3 months as "rather common" for young adult males.
I know of no-one who used only 13+ reps and got big from it. So probably a better rule of thumb is that under a dozen reps makes you stronger, and over a dozen makes you fitter... and whether you get bigger or smaller depends on your diet.
Or as Markos likes to say, strength and fitness under the iron, size at the dinner table. For hypertrophy, lift heavy and eat heavier.