If you have an idea how deep you want to spread your mulch or soil, all that is left to figure out is your total square feet of coverage. Start by measuring each individual area by itself by stepping off the length and the width. Each stride you make is approximately 3 feet in length. Multiply the length x width and you get the total square feet for that particular area. Repeat the step for each area to be covered, then add all the totals for your grand total. (Note: Do not add all lengths and multiply by the total of all widths. You will not have a correct total.)
A full size 3/4 or 1 ton pickup can hold 3 cubic yards, slightly rounded, but product weight must be considered. Most full size pickups can handle 3 yards of mulch, 2 yards of compost or 1 to 1.5 yards of soil product. If hauling rock product, a full size can handle between .5 and 1 cubic yard. Never load more than what is reasonable or what your vehicle is specified to carry. A smaller compact pickup will haul about 1/2 what a full size pickup will carry.