You can measure wheel holes by using the bolt pattern, which is the diameter of an imaginary circle formed by the centers of wheel lugs. It is also known as the bolt circle or pitch-circle diameter (PCD). Common bolt patterns are 4-, 5-, 6- or 8-lug holes. A bolt circle of 5x100 would indicate a 5-lug pattern on a circle with a diameter of 100mm. There are different methods of measuring PCD depending on how many lugs there are.
Find the PCD for a 4-bolt pattern by measuring the distance center-to-center between two holes directly across from one another, with a tape measure.
Find a close estimate of the PCD for a 5-bolt pattern by measuring the distance center-to-center between two holes across the hub from each other (there will be one hole in between on one side and two holes in between on the other). Multiply that measurement by 1.05 to get the estimate.
Find the PCD for 6- and 8-bolt patterns by using the same method as a 4-bolt. Measure center-to-center between two diametrically-opposed holes.
