There is no equivalence.
A yard is a measure of length or distance in 1-dimensional space while what is given in the question is a measure of volume in 3-dimensional space. The two measure different things and, according to basic principles of dimensional analysis, conversion from one to the other is not valid without some addition information.
How many square yards in a 20x18 feet 3 inches thick
four
50x100x4 = 20,000 cubic inches36 inches in a yard20,000/36 = 555 5/9 cubic yards.
It depends on what "5 thick" is: 5 inches thick, 5 feet thick, 5 yards thick, 5 miles thick etc.
1.62
10 yards
How many square yards in a 20x18 feet 3 inches thick
6.67 Cubic Yards
39.1116 cubic yards
four
4
You'll need a minimum of 1.85 cubic yards for that size.
50x100x4 = 20,000 cubic inches36 inches in a yard20,000/36 = 555 5/9 cubic yards.
It should be a little over 19 yards.
22.2222 cubic yards (the 2s keep on going).
151/9 cubic yards for every 12 inches thick
Depends on how thick it is. At 4 inches thick, you would nee about 5.5 cubic yards adjusting for safety. At 6 inches, you'd need about 8 cubic yards. You can play with different thicknesses with the linked concrete pad calculator.