I use this Metric Conversion Calculator on a daily basis while designing parts in CAD. Being raised to "think" in inches and feet makes it difficult for me to imagine metric measurements while designing. I find that this calculator helps and I think others here may find it useful so I thought I'd share it. I just keep a tab in my browser open and pointed to this link.
http://www.metric-conversions.org/length/millimeters-to-inches.htm
-Nugz
Metric Conversion Calculator 2014-11-17
Quickly convert measurements from mm to inch and vice versa.