When I first began buying khuks, I found the the length to be deceptive. For most knives, length refers to blade length, but length is typically the overall length in khukris. British issue khukris are 15-inch; I'd probably go for a 16.5" version if it's a broad blade, possibly up to a 20" if it's narrow. My limited experience is that that more narrow-bladed styles with a less pronounced curvature are less prone to binding in the sheath, and therefore draw more smoothly.