Hello,
As far as I am aware both MS SQL Server Express 2008 and Express 2012 limit ram usage per instance to 1GB. However right now I'm looking at a 2008 express server on a Windows Server 2008 Standard server, ram usage for the service pertaining to one sql instance is 1,858,812k which I make about 1.7 GB. Also have another server, it's a Windows Server 2012 Standard running SQL Server Express 2012 and just one sql instance there is using 3.7 GB of ram.
How is this happening?