3 Answers

You need 1.5 cu. yds. of concrete.  To compute that:  120 cu. ft. divided by 1/3 ft.(4 in.=1/3 ft.)=40 cu.ft

and in 1 cu. ft. there are 27 cu. ft.      so,  40 divided by 27 is 1.49 cu.yd. (so order 1.5 cu. yd.)

Do not be surprised if you cannot order less than a minimum order of perhaps 2 or 3 cu. yds. to get delivery.  So if that is the case, plan on doing additional projects at the same time, build a sidewalk, etc.  Do your homework, and plan accordingly!

The volume of a cube with the dimensions of 120 square ft and 4" is 135,921 liters / 8,294,400 squared inches. Volume cannot be expressed in yards because a yard is an area unit, not volume.

120sq ft would take 120/9=13.3333ex1 than since it's only 4'' thick so you need  13.3333/3=4.444 or 4& 1/2 yard of cement. round of to the nearest yard.A yard of cement is 12'' thick / 3x3 which is 9 sq ft.