Depends on how thick it is, think of your slab as a cube... We need to find how many cubic ft. Are in your slab because concrete is sold by the yard. 1 yard of concrete = 27 cubic feet..

L x W x H is the formula to calculate the volume of any cube..You have determined the square footage of your slab to be 240SQ ft. By multiplying L x W. Now we have to multiply that by the Height of the slab or cube.....

For example lets assume your slab is 4 inches thick...Length and Width are in feet, so we need to convert 4 inches into feet before we multiply it to our square footage number(240) I to get the cubic feet of the slab. .. To convert 4 inches into feet divide it by 12... 4/12 =.33

.33' Feet is the Height of our slab,, simply multiply it by the square footage which is 240...

.33 x 240 = 79.2

Assuming the Height of your slab is 4 inches you have 79.2 cubic feet in your slab...We know 1 yard of concrete = 27 cubic feet. .....next divide 79.2 by 27 to determine how many yards of concrete you need. ....72.9/27 = 2.93 or 3 yards of concrete. Always order a half a yard extra for variances, don't short yourself. I would get 3.5 yards for our example here..

I used 4 inches as an example because thats a very common dimension for a slab. Say its 5 inches or whatever use the same formula..

Hope this helps.

L x W x H is the formula to calculate the volume of any cube..You have determined the square footage of your slab to be 240SQ ft. By multiplying L x W. Now we have to multiply that by the Height of the slab or cube.....

For example lets assume your slab is 4 inches thick...Length and Width are in feet, so we need to convert 4 inches into feet before we multiply it to our square footage number(240) I to get the cubic feet of the slab. .. To convert 4 inches into feet divide it by 12... 4/12 =.33

.33' Feet is the Height of our slab,, simply multiply it by the square footage which is 240...

.33 x 240 = 79.2

Assuming the Height of your slab is 4 inches you have 79.2 cubic feet in your slab...We know 1 yard of concrete = 27 cubic feet. .....next divide 79.2 by 27 to determine how many yards of concrete you need. ....72.9/27 = 2.93 or 3 yards of concrete. Always order a half a yard extra for variances, don't short yourself. I would get 3.5 yards for our example here..

I used 4 inches as an example because thats a very common dimension for a slab. Say its 5 inches or whatever use the same formula..

Hope this helps.