What the font????

i cannot for the life of me figure out this dumb font system. everytime i choose arial and normal size it comes out too small. so the next time i try arial and large which is what im typing in now. comes out looking ok but when i use those exact same settings again it comes out looking completely different. i just want to find one setting that looks decent and is readable. is that so much to ask as a new blogger?? honestly.....