Do you have to use pixels? The conversions I found is a tracking value of 1000 is equal to 1 em in CSS, so in your case tracking 100 should be 0.1 em.
EDIT
To go from EM to pixels use this site PXtoEM.com. For your specific case 0.1 em converts to 2px. However this is based on a 16pt font, so you will have to adjust for the specific font size you’re using.