How to stop font resize of input?

How do you stop Mathematica from resizing the input font when entering formulas with fractions and such? When I enter a formula with a few fractions the text becomes microscopic. For example:

100 ((1 + tops[[i]]/100)/(1 + bottoms[[j]]/100) - 1)


You see that the 100 is at normal input text size but the fractions go tiny. I prefer to input in the notebook in traditional notation. This auto resizing makes it a bit painful to read.

Edmund