Ubuntu calculator in dash
This seems to be because the Home lens doesn't search the "info" group of scopes by default, which include the calculator scope.
To enable follow the steps linked below and add 'info.scope' to the always-search list.
How to change default "Categories" and "Sources" in Unity Dash?
Type
sudo apt-get install unity-scope-calculator
You will get a message saying it is already installed.
In order for the results of calculations to show up, you have to filter the results to calculations, located at far right in filters. Worked for me.