CalcPad is a note taking app with powerful calculator built in. It can perform basic calculations as well as complex unit conversions, real time currency conversions and percentages. It can even handle variables and custom functions if you need them.
With a handy menubar icon, global access shortcut and window options, it will be your ultimate go-to app for fast note taking and napkin math needs.
Don't forget to check macOS App Store for the Mac version!