Taking Measurements for Driveway Project
Measure the area of the driveway using a tape measure, walking wheel, or whatever is most appropriate for the size and layout of your driveway. If your driveway is rectangular, just multiply the length (in feet) by the width (in feet). If it's a more complicate shape, break it into smaller shapes that are rectangles, and add the area of each smaller shape together. 

Take the area and multiply it by the depth of sand you wish to have, in inches. Divide that by 12, and the result is the number of cubic feet of sand you'll need. Divide that by 27 to get the number of cubic yards you'll need.

You'll probably want to add some fudge factor to account for measurement errors, the driveway edges not being straight, dips in the driveway, etc. How much depends on the size of your driveway, but 10% is probably a good starting point.