The multi-functional Google Calculator is now available in the Google Play Store.

The app will do all of the basic math like addition, subtraction, multiplying
and division. And if you have more complex problems to be solved, putting the phone into landscape mode will turn the calculator into a scientific calculator
with buttons for sine, cosine, tangent, logarithm and pi.

The scientific calculator function is also available with the phone in portrait by swiping to the left. A panel will slide out containing all of the buttons
required for more complex computations. And yes, the app does support Android Wear.

If you're unhappy with the calculator that comes on your Android phone, you can always install the official Google Calculator from the Google Play Store.
And you won't need a calculator to figure out how much it will cost you since the app is free.