Try changing the text size of your browser (make sure you're not just zooming the view).
Relative sizeActual pixel size (px)
1em16
1ex9
100%16
12pt16
16px16
xx-small9
x-small10
small13
medium16
large18
x-large24
xx-large32
Scrollbar measurements: {w:0 h:0 }
Font measurements: {1em:16 1ex:9 }