Quick Calc on Mac

1. Click on Apps icon - Select calculator Or open spotlight, type calculator and select the first option to launch calculator. Type in your numbers and operators to get the result, seems to be the most used one. 
2. You can also use Dashboard (by pressing F4) and calculator should be there by default.
3. BUt the easiest of them if your data isn't very complex is just open spotlight (cmd-space) and type in your data there... For e.g., 3^4*2 and the first result is your answer. :)