Sounds about right. 32GB with 27GB free space is roughly 5GB of data. Backjups only back up the data, not free space, so the backup being around 4GB (allowing for rounding and different conversions of MB to GB, 1000 vs 1024), 4GB backup sounds correct.
Gail Shaw
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability