There are countless apps for adding fractions and giving decimal equivalents; I’ve used a bunch of them and Fraction Plus is by far the easiest to use. The interface is simple and it is not burdened with all kinds of functions you will never use. If I need to do something more complicated I can go to my construction calculator. But for the basics this app is good. Yes, we can all add fractions in our heads and give a decimal equivalent to the basic fractions we use, but when adding a run of dimensions together this app is an invaluable tool.
Fraction plus is available for iPhone, iPad, and Android devices. A free version exists but I spent the 99 cents it costs to use the app without annoying ads.