You can measure your nails in two ways- with a soft ruler or a string & ruler. If you have a soft ruler, you can hold one end of the ruler at one side of the nail. Measure across your fingernails and read off the measurements. If you have do not have a soft ruler, simply repeat the steps above but use a string. Tie a knot to one end and measure across your fingernails. Measure the string with a regular ruler.