SQL Database initial size

Hi,

I need your Advice.

Details as fallows: Existing DB setting in Production DB (SQL Server 2005)

Total Database size: 316686.25 MB (Sql Management Studio-->Database-->Properties--General)

Space Available:  118.13 (Sql Management Studio-->Database-->Properties--General)

                                    Initial Growth         Auto Growth

Initial Growth : .mdf -->139,993 MB           By 10 MB, unrestricted growth     D:\    Free space 92 GB

                         .ndf -->6585 MB                By 10 MB, unrestricted growth     E:\     Free space 57 GB

                         .ndf-->166911 MB             By 10 MB, unrestricted growth     F:\     Free space 12 GB    (This files is growing rapidly)

My database growth is per month around 10-12 GB.

Please advice me that is it necessary to increase Space Available or the existing 118.13 is sufficient or not.