#### The old-fashioned mathematical formula way and the shortcut way

Tim Odell, of Odell Complete Concrete, describes a straightforward process for bidding out concrete for the curvy jobs.

#### Two methods for calculating the area of a circle

- You can do the pi*r
^{2 }method, where pi = 3.141592..., r = the radius of the circle, and squared is squared. - Or, you can shortcut to a ratio: a circle within a square box occupies 78.5% of the space.

For a circle that is 10 feet wide, the box would be 10 feet x 10 feet = 100 square feet, making the circle 785 sq ft.

For sizes other than 10 x 10, multiply the square footage by (.785) to find the area of the circle. The example in the video has a slab that is a quarter-circle occupying an 18 feet x 18 feet box.

- 18 x 18 = 324; 324 x .785 = 254.35 square feet
- (3.14) x (18
^{2}) = 3.14 x 324 = 1017.36; divided by 4 (because it is a quarter of the circle) = 254.34 square feet

Notice that in the first method, you don't have to multiply the square footage to account for the whole circle and then divide back down to a quarter-circle.

#### To determine yardage for a concrete order, factor in the thickness of the slab

In the example of the video, the slab will be four inches thick.

- The first step is to convert four inches to feet so that the dimensions will be consistent. Four inches is .3333 foot. (254.34 square feet) x (.3333 foot thickness) = 84.77 cubic feet
- Next, convert cubic feet to cubic yards. There are 27 cubic feet in one cubic yard (3 x 3 x 3 = 27). Divide the cubic feet by 27 to determine cubic yards: 84.77 / 27 = 3.14 cubic yards.

Experienced concrete installers usually add a little to what they calculate because the real world is usually different from a piece of paper. Tim says that he will order about 3.5 or 3.75 yards of concrete for this.

*—Odell Complete Concrete is located in southern Calif, but their YouTube channel is everywhere.*