Concrete101: Estimating

Concrete work from a DIY perspective can be a difficult process, even if it's just a small amount to pour. That's why it's important for the average homeowner to learn the basics of each particular process of concrete from beginning to end. This will ensure that everything comes out right the first time. After all, concrete can only be poured once.

The first step is to use the blueprint or drawing of the actual dimensions of the slab. These dimensions are length, width and height or thickness of the slab (add ¼" for waste). Now multiply these dimensions and you get the square footage amounts. Problem: concrete is measured in yards! No problem: Simply divide the answer by 27 and you get the correct amount of concrete needed for your slab.

But what do you do when you have footings? What about columns and steps? Don't worry, Construct101 has got you covered. Check out our concrete calculator for these tough concrete estimates.

Odd shapes can sometimes throw a loop into the mix when estimating concrete. Where diagonal lines meet perpendicular lines, confusion can ensue. A driveway apron where it meets the road is a prime example. Calculate the average distance between the largest and smallest measurement of the diagonal area.

For example if a driveway measured 20 feet wide at the road and 16 feet the rest of the way up the driveway, the mean measurement would be 18 feet wide for the diagonal section that abutted the roadway and 16 feet for the remaining driveway.

Breaking concrete slabs into square and rectangular sections works best when estimating complex shaped slabs. This is especially true for footers. Footers will also need to have rebar calculated into the picture. Simply add the width and length of the slab to find the area and multiply it times two. The sum is the amount of square feet you need for rebar. It must be divided by 20 since rebar comes in 20 foot long sections.

Depending upon the size of your concrete pour, you may want to use bags or a ready-mix delivery service. The basic rule of thumb is a ready-mix will only bring out a truck if the delivery size is at least within 50 miles of their yard, is more than three yards and adequate access is available for the truck to deliver the mix. A concrete pump can be rented for hard to access areas.

If you have less than three yards of concrete getting bags is going to be your best bet. When you're tipping the scales at close to three yards, you may want to rent a concrete mixer to mix the many bags it will take to complete the pour in a fluid motion. Bag amounts come in 40, 60 and 80 pound sizes. Calculate the correct amount per bag size at Construct101's concrete calculator.