Sample backup compression figures – SQL Server 2012.  The relative sizes and timings are interesting. This was a database with data that compressed well.

• Uncompressed backup file:  73.4GB.  18 minutes to create
• Compressed backup:  17.5GB.  About 20 minutes to create
• Compressing the 73.4GB backup file using 7-zip:  9.7GB.  About 2 hours to compress.