Rebar Cost Calculator — Free Quantities + Pricing Estimator

How Rebar Is Estimated

Rebar is quoted two ways and both matter. The supplier sells it by the linear foot (or by the pound, which is the same thing once you know the bar size); the concrete contractor prices it by the square foot of slab. This calculator gives you both. On the 20 x 20 ft reference slab in #4 (1/2") that is $1.27 per linear foot installed and $1.73 per square foot of slab — the same $692, read two ways.

The quantity comes out of the grid geometry, not out of a rule of thumb. At 18" O.C. both ways, a 20 x 20 ft slab takes 546 linear feet of bar in 28 standard 20-foot lengths, allowing 3 inches of cover at each edge. That is what the free estimate prices, plus a per-square-foot allowance for chairs and tie wire and the placement labor to tie it off.

Two things the free estimate deliberately does not vary. Spacing is fixed at 18" O.C. — the selector is a Professional-mode input. And slab thickness does not change the number, which is correct rather than a limitation: at a fixed spacing the bar quantity is set by the plan dimensions of the slab, not its depth. A thicker slab needs taller chairs, not more steel. If your engineer has specified a tighter grid or a second mat, price it in Professional mode.

Rebar Cost by Bar Size on a 20 x 20 ft Slab

Bar size is the specification input the free calculator gives you, and it is the one that moves the bill hardest — not because the bars cost more each, but because heavier bar costs more per foot and weighs more per foot, and placement labor is billed by the pound. Every row is a separate execution of the estimate on the same 400 square foot slab, so the linear footage and the bar count are identical down the table and only the steel changes.

Note what the $/lb column does: it is lowest in the middle of the range, not at either end. On light bar the per-square-foot allowance for chairs and tie wire is a large share of a small bill, which pushes the per-pound figure up; it bottoms out around #5 (5/8") at $1.82, then ticks up again on the heaviest sizes because their per-foot rates step up faster than their weight does. If you are choosing between two sizes, compare the installed totals in the last column rather than reasoning from weight.

Rebar Quantity and Cost by Slab Size

Linear footage does not scale with area quite as cleanly as you would expect, because the grid is laid out from the edges in and every run loses 6 inches to cover. Small slabs pay a penalty for that; large ones barely notice it. All rows are #4 (1/2") at 18" O.C..

What the Materials Cost: 20 x 20 ft Slab, Line by Line

This is the same 20 x 20 ft slab worked at the top of the page, broken out the way you would actually buy it. The lines below add to the $692 installed figure exactly, and the build fails if they ever stop doing so. The last line is the balance between the shopping list and the installed price — the crew that ties it off.

One honest note on reading this list against the DIY figure the calculator shows after you press Calculate. They are not the same number and they are not meant to be: the takeoff prices whole 20-foot bars, because that is how they are sold, while the DIY figure bills the 546 feet the mat actually consumes, adds a contingency and leaves out the cutter rental. On this slab the list comes to $629 against a DIY figure of $681.

Rebar Cost by Metro Area

Reinforcing steel is a commodity priced off the same mills nationwide, so what varies between markets is the crew that places it — which is most of the spread below. These are the complete regional factors this calculator applies, not a selection. Type the ZIP in the second column into the ZIP field above and the calculator will price your own slab at that factor. The cost column is the same 20 x 20 ft reference slab, so the rows are comparable to each other and to the national $692 above.

The factor is applied to the whole estimate rather than to the steel alone. If your ZIP is not in this list the calculator prices at the national baseline rather than guessing at a factor it does not have.

Frequently Asked Questions