The judgement of whether or not a woman is worthy of sexual intercourse by means of a rough measurement of the width her buttocks. This measurement is conducted by forming two "hang loose" hand gestures and making touching one's thumbs together. Some gentlemen have been known to give some leeway in regards to this measurement by allowing an approximate half inch gap between the thumbs.
You see your friend chatting with a slightly plus-sized woman. You then inform him of this woman's slight weight issue by exclaiming, "make it fit".