If the units are 30 ft x 30 ft x 4 inches, then you have 30 x 30 x 0.33 ft = 300 cubic feet
300 cubic ft/27 cu yds/cu ft = 11.1 cubic yards
You will need 17.8 cubic yards of concrete.
10.67 Cubic Yards
10 yards
6.67 Cubic Yards
15 cubic yards
You will need 17.8 cubic yards of concrete.
10.67 Cubic Yards
532.4074 yards of concrete, round up to 533 yards.
3.6 cubic yards will be enough.
6.94 Cubic Yards
10 yards
6.67 Cubic Yards
4.074 cubic yards for every foot the slab is thick.
15 cubic yards
15 cubic yards
39.1116 cubic yards
At 4" thick you will need 1.23 cubic yards.