I have found that when I use the 4-7/8" measurement to make HSTs, the HSTs are always too small. So I use the 5" squares, draw the line down the center, sew and trim. A little more work, but better to trim than be too small. Plus, when you cut the squares into triangles, you are working with bias edges and can stretch your HSTs out of shape.
I've also seen a new method where you take two large squares, draw 2 diagonal lines on the lighter fabric, put the right sides together and sew 1/4" on both sides of all the lines. Then cut on the line, and you have 4 HSTs, which you will probably have to trim.
There are several rulers out there for trimming HSTs -- Eleanor Burns QIAD, June Tailor Shape Cut and the one with the groove down the middle (sorry, but the name escapes me), along with the square up rulers.