I found a guideline for how to judge fermented beverages callled the Beer Judge Certification Program or BJCP. This “BJCP Style Guideline” (rev 2008) states the following limits for characterization of mead:
For FG
0.990 – 1.010 “dry mead”
1.010 – 1.025 “semisweet mead”
1.025 – 1.050 “sweet mead”
For OG and ABV
Hydromel:
1.035 – 1.080
3.5% – 7.5%
Standard mead:
1.080 – 1.120
7.5% – 14%
Sack mead:
1.120 – 1.170
14% – 18%
Just for fun, Ken Schramm has the following definitions for sweetness in his book (2003):
0.990 – 1.006 “dry mead”
1.006 – 1.015 “medium mead”
1.012 – 1.020 “sweet mead”
1.020 – N.A. “dessert mead”
Notice how BJCP has a mead at for example 1.023 to be considered as semisweet, whereas the same mead would be considered a dessert mead by Ken Schramm :o).
Just remenber, that these are just numbers to describe some basic characteristics of mead. Whether you enjoy the smell, taste, and mouth feel will always be an individual experience.