What are the dimensions of the car rims?

If it's urgent, take out a tape measure, and measure from the center of one hole to the center of the opposite. That will give you the bolt pattern (expressed as 4x#, most likely you will want to convert it to metric. IE 4x100.). Then you need to know the backspacing, which is how far the wheel sticks into the fender, over the brakes, basically. 0 backspace means the mounting surface of the wheel is flush with the backside of the wheel. A positive offset wheel will have a backspacing that's greater than 1/2 the width of the wheel (if you have a 5" backspacing on a 17x8" wheel, it's a positive offset). Meanwhile, a negative offset will have a backspacing value less than 1/2 the width (3.5" backspacing on a 17x8" wheel). A neutral offset would be right in the center (4" backspace on an 8" wide wheel).

there is more than just finding the right amount of wheel nut holes, you will also need to factor in the off set you will need. what car is it for? model and year always help what sized rim you want, be it 15 16 17 18.