It may seem like a daunting task as you face a giant slab of concrete as you plan your next DIY project. But estimating how much rebar you need or where rebar lies within an existing concrete wall or slab isn't terribly difficult. A little math and some time will give you a rather solid estimate for a rebar takeoff. Calculating how much rebar you need is rather simple once you understand the basics of building for your particular project.

Reinforcement metal framework.
credit: fotolism_thai/iStock/GettyImages
How to Do a Rebar Takeoff

Rebar Background

Concrete is weak in tension so strong rods of rebar are added in order to deliver tensile strength to walls and borders. Rebar is used in outbuildings, retainer walls, backyard boundary walls and patio slabs among other projects around the homestead. Rebar will help ensure that your concrete or cinder block project construction is strong and crack proof. Don't underestimate the importance of using rebar in your project.

There are different types of rebar to choose from. A concrete path or patio incorporates a number three bar every 18 to 24 inches. For driveways, you'll need a number four bar closer together at a foot to 18 inches apart. Rebar is laid in a grid pattern for ground projects while walls require more vertical support.

Elementary Calculations

Rebar is manufactured and sold in 20-foot lengths. From that rudimentary measurement, you can estimate how much rebar you will need for your project. You'll need to know the slab length and width for walkways and patios, height and footers for walls and grid spacing and edge clearance for both in order to clearly calculate how much rebar you'll need for most projects.

You'll need to count and measure all of the rebar in your footings as well as the walls to complete the rebar takeoff, or at least determine an estimation. Be prepared to spend some time to get an accurate estimate. A small project such as a backyard border wall should take no more than a few hours whereas a larger project could take up to 12 hours.

Count the rebar in your footers first. Footers that are two-feet wide need three sticks of rebar. If your footers are 16 inches they'll have two rebars for support. As rebar is made in 20-foot lengths, divide your footer length by 20 to find the footage of rebar you have total in just the footers. Now multiply the total rebar by the number needed for your particular footer width you've measured, not guessed. If you have five footers at 24 inches in length, you have 120 inches of footer. Divide that by three for a total of 40. You will need 40 sticks of rebar to finish your project.

Adding rebar will reinforce your project so it won't crumble or crack over the years as you use and enjoy your DIY patio, retainer wall or driveway.