how do i figure yards of concrete by the running foot of my forms?

First, you calculate the volume of one linear (running) foot of your forms. Then multiply that volume by the length of your forms. Just keep all the units the same. I start with cu-in, then convert to cu-ft, then to cu-yd.

Example A)

10"x10" x 12" = 1200 cu-in

Divide by 1728 (# of cu-in per cu-ft): 1200 / 1728 = 0.694 cu-ft per linear foot of forms.

Since there are 27 cu-ft per 1 cu-yd, each linear foot of this form

requires 0.0257 cu-yds of concrete.

Thus, 100 linear ft of this form would need 2.57 cu-yds of concrete.

Example B)

12"x15" x12" = 2160 cu-in

2160 / 1728 = 1.25 cu-ft per linear foot

1.25 cu-ft / 27 cu-ft / cu-yd = 0.0463 cu-yds of concrete

Thus, 100 linear ft would need 4.63 cu-yds of concrete.

* 12 x 12 x 12 = 1728 cu-in per 1 cu-ft.

* 3 x 3 x 3 = 27 cu-ft per 1 cu-yd

12x12 x thickness = cubic feet /27 =cubic yards.

Thickness

.334 = 4"

.5=6"

.667=8"

.85=10"

1 = 1 ft

/27

Find the volume of your forms in cubic feet.(10 inches = .833 feet, 15 inches = 1.25 feet). Example: 10 inches deep X 1 foot wide=.833 square feet, times the length, say 22 feet for a strip footing =18.326 cubic feet. Divide this by 27(the number of cubic feet in one cubic yard) and you get .678 cubic yards or approximately 3/4 of a yard for this example. Remember, multiply depth X width X length = cubic feet divided by 27 = cubic yards. To convert inches to feet divide inches by 12(5 inches divided by 12 =,416 feet)

Ohh,, I could show you how to work out the math,, but if you run down the any construction supply place you can pick up a VERY nifty calculator for about $80. that will do all your figuring needs.