How to convert feet and inches to decimal feet?

What is the proper way of converting feet inches to decimal feet?

For example

15 ft - 4, 1/8 inch = 15.34'

I understand that the 15 get's moved but how do you take 4 1/8" and turn that into 0.34?

What is the proper way of converting feet inches to decimal feet?

For example

15 ft - 4, 1/8 inch = 15.34'

I understand that the 15 get's moved but how do you take 4 1/8" and turn that into 0.34?