How does the number in stellar classification indicate properties within the range of that class?
Here is a table taken from the models of Siess et al. (2000). It is appropriate for zero age main sequence stars of about the solar metallicity. Note that any correspondence between spectral type, mass and radius will be age dependent.

You can generate tables for different metallicities, or get more detailed information at http://www.astro.ulb.ac.be/~siess/pmwiki/pmwiki.php?n=WWWTools.Isochrones

Computation of the ZAMS
Metallicity : Z = 0.02 , no overshooting

 ST       L         R        Teff     Mass     age       Bol    BC     B-V    V-R    V-I    Mu     Mv     Mb     Mr     Mi     Mj     Mh     Mk     Ml  flag  check

 M6   8.290E-04  1.137E-01   2781.   0.100  2.270E+10  12.45  -5.97   2.28   2.76   5.68  22.15  18.42  20.70  15.66  12.75  10.49   9.77   9.32   8.85   1     1

 M5   6.689E-03  2.187E-01   3300.   0.200  1.785E+08  10.19  -2.95   1.72   1.37   3.15  16.12  13.14  14.85  11.76   9.99   8.33   7.72   7.42   7.16   0     0

 M3   1.488E-02  2.950E-01   3528.   0.300  1.343E+08   9.32  -1.88   1.54   1.05   2.33  13.94  11.20  12.73  10.14   8.86   7.64   7.00   6.77   6.59   0     0

 M2   2.656E-02  3.612E-01   3683.   0.400  1.120E+08   8.69  -1.51   1.48   0.96   2.03  12.89  10.20  11.68   9.24   8.17   7.10   6.43   6.23   6.08   0     0

 M1   4.633E-02  4.293E-01   3829.   0.500  1.019E+08   8.09  -1.24   1.43   0.90   1.82  11.98   9.32  10.75   8.42   7.51   6.56   5.88   5.71   5.58   0     0

 M0   8.292E-02  5.215E-01   4008.   0.600  8.320E+07   7.45  -1.05   1.37   0.86   1.67  11.08   8.50   9.87   7.64   6.83   5.97   5.31   5.16   5.04   0     0

 K6   1.481E-01  6.369E-01   4287.   0.700  6.587E+07   6.82  -0.75   1.21   0.75   1.39   9.88   7.57   8.78   6.83   6.18   5.40   4.79   4.67   4.56   0     0

 K4   2.804E-01  7.561E-01   4698.   0.800  5.212E+07   6.13  -0.51   1.00   0.60   1.11   8.47   6.64   7.64   6.04   5.54   4.82   4.27   4.17   4.08   0     0

 K2   4.877E-01  8.656E-01   5047.   0.900  4.173E+07   5.53  -0.38   0.86   0.51   0.94   7.35   5.91   6.77   5.40   4.96   4.36   3.88   3.79   3.73   0     0

 K0   8.102E-01  9.973E-01   5334.   1.000  3.326E+07   4.98  -0.30   0.80   0.45   0.85   6.48   5.28   6.07   4.82   4.43   3.90   3.46   3.39   3.33   0     0

 G8   1.297E+00  1.166E+00   5556.   1.100  2.653E+07   4.47  -0.25   0.73   0.42   0.80   5.72   4.71   5.44   4.30   3.91   3.44   3.04   2.97   2.92   0     0

 G5   2.004E+00  1.332E+00   5788.   1.200  2.214E+07   4.00  -0.21   0.65   0.39   0.75   5.02   4.20   4.85   3.82   3.45   3.06   2.71   2.65   2.60   0     0

 G0   2.946E+00  1.476E+00   6070.   1.300  1.915E+07   3.58  -0.18   0.56   0.35   0.70   4.33   3.75   4.32   3.41   3.05   2.71   2.41   2.36   2.31   0     0

 F7   4.281E+00  1.656E+00   6284.   1.400  1.617E+07   3.17  -0.16   0.49   0.31   0.62   3.82   3.33   3.82   3.02   2.71   2.38   2.08   2.04   2.00   0     0

 F5   6.065E+00  1.848E+00   6498.   1.500  1.370E+07   2.79  -0.14   0.41   0.27   0.53   3.33   2.93   3.34   2.66   2.40   2.13   1.90   1.86   1.82   0     0

 F3   8.117E+00  1.968E+00   6770.   1.600  1.196E+07   2.48  -0.12   0.37   0.24   0.48   2.97   2.59   2.96   2.35   2.12   1.91   1.73   1.70   1.67   0     0

 F1   1.087E+01  2.062E+00   7120.   1.700  1.031E+07   2.16  -0.10   0.32   0.21   0.43   2.61   2.26   2.58   2.05   1.83   1.70   1.56   1.53   1.50   0     0

 A9   1.405E+01  2.129E+00   7476.   1.800  9.064E+06   1.88  -0.10   0.25   0.15   0.35   2.29   1.98   2.23   1.83   1.64   1.51   1.41   1.38   1.35   0     0

 A8   1.784E+01  2.202E+00   7832.   1.900  8.004E+06   1.62  -0.12   0.20   0.10   0.27   2.02   1.74   1.93   1.63   1.47   1.34   1.26   1.23   1.20   0     0

 A7   2.226E+01  2.268E+00   8176.   2.000  7.125E+06   1.38  -0.13   0.17   0.08   0.21   1.77   1.51   1.68   1.43   1.30   1.17   1.10   1.07   1.04   0     0

 A3   3.330E+01  2.395E+00   8824.   2.200  5.731E+06   0.94  -0.19   0.08   0.03   0.07   1.26   1.13   1.21   1.10   1.06   0.97   0.95   0.94   0.93   0     0

 A0   5.441E+01  2.512E+00   9705.   2.500  4.298E+06   0.41  -0.38  -0.02   0.00  -0.03   0.73   0.80   0.78   0.80   0.82   0.84   0.85   0.86   0.87   0     0

 A0   7.341E+01  2.618E+00  10241.   2.700  3.595E+06   0.09  -0.49  -0.04  -0.01  -0.05   0.42   0.57   0.53   0.58   0.63   0.68   0.70   0.72   0.73   0     0

 B9   1.059E+02  2.720E+00  11048.   3.000  2.815E+06  -0.31  -0.63  -0.07  -0.01  -0.07   0.06   0.32   0.26   0.34   0.40   0.49   0.53   0.55   0.58   0     0

 B8   1.843E+02  2.940E+00  12094.   3.500  1.944E+06  -0.91  -0.82  -0.09  -0.02  -0.09  -0.48  -0.09  -0.19  -0.08   0.00   0.15   0.19   0.23   0.26   0     0

 B7   3.172E+02  3.240E+00  13208.   4.000  1.387E+06  -1.50  -1.06  -0.11  -0.02  -0.09  -0.97  -0.45  -0.56  -0.42  -0.35  -0.15  -0.10  -0.04  -0.02   0     0

 B6   6.822E+02  3.530E+00  15334.   5.000  7.917E+05  -2.33  -1.45  -0.14  -0.04  -0.11  -1.61  -0.89  -1.03  -0.85  -0.78  -0.53  -0.47  -0.37  -0.40   0     0

 B4   1.343E+03  3.910E+00  17291.   6.000  4.852E+05  -3.07  -1.75  -0.17  -0.05  -0.14  -2.17  -1.32  -1.48  -1.26  -1.18  -0.91  -0.83  -0.73  -0.75   0     0

 B3   2.366E+03  4.320E+00  19281.   7.000  3.223E+05  -3.69  -2.06  -0.20  -0.07  -0.17  -2.60  -1.62  -1.82  -1.55  -1.46  -1.14  -1.05  -0.97  -0.95   0     0


The ZAMS is defined as the time, after deuterium burning, when Lnucl > 0.99 L (i.e. Lgrav &lt; 0.01 L)

L,R and M are expressed in solar units, Teff in K

Bol represents the bolometric magnitude
Colors are given in the Cousins system. We used the conversion table of Kenyon et al. (1994, AJ, 108, 251)
check = 1 means that the colors are out of the table and have been extrapolated
flag  = 1 means that the request was not successful. The data corresponds to the last entry found in the file