This Aspect Ratio Calculator (ARC app) helps with resizing calculations. Great for when you need to resize images!
You supply the original X and Y for a dimension along with the new X dimension and it will calculate the new Y value. Or if you know you need the new size as a factor of the original, it will calculate that for you as well. Choose from a factor of 1/4, 1/3, 1/2, 2, 3 or even 4 for automatic calculations.
Answers can be displayed with decimals or as whole numbers.