# How to Calculate Rebar Quantities Based on Square Feet & Center

Share It

There's money to be made in pouring concrete, but it's a lot more complicated than "mud pies for grownups." You'll need to know which mix is right for which jobs, how many yards of concrete you'll need to order and – crucially – how much rebar you'll need to reinforce that concrete so it holds up over time and use. The math isn't especially difficult, but you'll need to master it before you can give your potential clients an accurate quote.

## Arriving at Your Spacing on Center

In an ideal situation, you'll quote based on architectural drawings that specify what size of rebar you'll use and what the spacing should be from center to center. In a less formal setting where you're pouring a slab in an existing space without formal plans, you'll have to do a bit more research.

## Calculating What You Need

For the sake of easy examples, assume you're pouring a slab that's a simple rectangle of 20 by 30 feet, and you've figured out that you'll need the rebar set at 14 inches on center. Start by multiplying each of those measurements by 12 to get your dimensions in inches, which in this case would be 240 inches by 360. Now, divide each measurement by the 14-inch spacing. For the short side, 240 inches divided by 14 inches gives you 17 lengths of 20-foot rebar plus a bit left over. Add one more length to allow for that extra, giving you a total of 18. For the slab's longer dimension, you'll need 360 inches divided by 14, which gives you 25 plus a bit left over. That means you'll need a total of 26 lengths of 30-foot rebar.

## Converting to Weight

Depending where you live and how much rebar you're ordering, you may not always have the option of ordering it by the individual piece. Instead, you might be ordering by weight. Converting isn't that big of a challenge because most manufacturers and suppliers provide you with the weights of their rebar on their websites. First, add up the total length of rebar you need. In this example, you'd need 18 lengths at 20 feet for a total of 360 linear feet. You'll also need 26 at 30 feet for a total of 780 linear feet. Put those together, and your total order is 1,140 feet of rebar. Now, look up the weight of your rebar. If you're using #5 bars, for example, they come in at just over a pound per foot – 1.043, to be precise. Multiply that by your 1,140 feet, and you'll find you need to order 1,189 pounds of rebar.