You need to supply the thickness of the slab in order to calculate this.
If it was a 6" inch thick slab (0.5 feet), then the formula would be 2 x 76 x 0.5, all divided by 27 = 2.81 cubic yards.
4.074 cubic yards for every foot the slab is thick.
how many yards of concrete will i need to do a 20 x20 x4 slab
37.03 yards
How many square yards in a 20x18 feet 3 inches thick
3.95 cubic yards of cement are needed for a slab that size.
A 40x60x6in slab requires 44.44 cubic yards of cement.
18x32 feet by 4 inches thick: 7.1 cubic yards. For a 6-inch slab, 10.7 cubic yards.
1.19 Cubic Yards
about 5 yards if your slab is 4" deep
You can't express a volume of concrete in yards.
10.67 Cubic Yards
1.85 cubic yards.