Qalculate!

Qalculate! is the Android version of the desktop calculator many people already keep on their computer. You write what you mean, like "15% of 80" or "3 miles to km", and it works the answer out, converting units and currencies along the way.

Behind the ordinary-looking keypad sits libqalculate, the same engine the desktop app uses: a large library of functions, physical constants, variables you can define yourself, symbolic maths including integrals and equations, arbitrary precision and uncertainty propagation. There is a plain default view for quick sums, and an optional calculate-as-you-type mode that shows the result while you are still writing.

The deeper features have a syntax worth reading up on. The Qalculate! manual on the project's website lists all the functions, units and variables. This Android front end is a younger project than the desktop one, so expect it to keep changing.