XXL Calculator is calculator with extra-large buttons and display.
It supports the basic operations, percent calculation, squaring, cubing and square root calculation.
Additionally, it has a memory function and you can toggle between a dark and light color theme.
The calculator is especially handy in snapped or compact view, as you can have it active aside your main document for doing quick calculations.
And it has full keyboard support, including copy & paste (Ctrl-C and Ctrl-V).