A wall is not a flat slab — count verticals along its length, horizontals up its height, then split the takeoff from the order
← Back to the calculatorVerticals are counted along the wall's 24 ft length: clear 285 in ÷ 16 in = 17 spaces + 1 = 18 bars, each 7.75 ft tall. Horizontals are counted up the wall's 8 ft height: clear 93 in ÷ 16 in = 5 spaces + 1 = 6 bars, each 23.75 ft long. Takeoff = 18 × 7.75 + 6 × 23.75 = 282 ft.
Open the calculator for the bar counts and weight, or read the four steps below for a wall.
Search for a rebar calculator for a wall and almost everything that comes back is a slab calculator with the words changed: it asks for a length and a width and treats the wall as a flat panel. A wall is not flat. It is a standing panel with two bar directions that come off two different dimensions — and the bars in one of those directions are longer than a stock bar, so they lap.
The two directions are not interchangeable. The vertical bars are the ones standing up, and there are as many of them as the wall's length allows. The horizontal bars run along the wall, and there are as many of them as the wall's height allows. Swap the two dimensions and you get a plausible-looking number that is simply wrong, which is the first mistake to rule out.
The second thing a wall does that a slab does not is separate the takeoff from the order. A wall is normally longer than one stock bar, so its horizontals lap; the verticals, being about as tall as the wall, usually do not. That means the steel you count on the drawing and the steel you buy are two different figures, and the gap between them is what this page is about. Everything below runs on a 24 ft × 8 ft wall in #4 bar at 16 in on centre with 1.5 in cover.
The vertical bars are spaced along the wall, so their count comes from the wall's length, and each one is as tall as the wall. Measure the clear length — the wall length minus a cover at each end — and apply the same rule every other rebar count uses:
The + 1 is a bar at the start of the run, exactly as it is a bar at the start of a row on the spacing page. The vertical's length is the wall height less the top and bottom cover — the bar does not run the full 8 ft, it runs the 8 ft minus the 1.5 in it is held off the top and the 1.5 in off the bottom.
The horizontal bars are spaced up the wall, so their count comes from the wall's height, and each one is as long as the wall. Same rule, different dimension:
Notice how the two dimensions cross over: the vertical count used the 24 ft length and the horizontal count used the 8 ft height, and the two bar lengths are the opposite way round again — the vertical is 7.75 ft (the height) and the horizontal is 23.75 ft (the length). This crossing is the whole wall takeoff, and it is the step a slab-shaped calculator cannot do, because a slab has no up.
| Direction | Counted from | Clear | Bars | Each is | Total |
|---|---|---|---|---|---|
| Vertical | wall length (24 ft) | 285 in | 18 | 7.75 ft (the height) | 139.5 ft |
| Horizontal | wall height (8 ft) | 93 in | 6 | 23.75 ft (the length) | 142.5 ft |
| Takeoff | — | — | 24 bars | — | 282.0 ft |
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282 ft is the takeoff: the net steel the drawing needs. It is the right number for pricing the job, and the wrong number to hand a supplier, because bar is sold in whole stock lengths. The order rounds every bar mark up to whole bars, and adds a lap wherever a bar is longer than the stock.
| Figure | Bars | Stock | Length bought | Weight | Laps |
|---|---|---|---|---|---|
| Takeoff (net) | 24 pieces | — | 282.0 ft | 188.4 lb | 0 |
| Order, 20 ft stock | 17 bars | 20 ft | 340 ft | 227.1 lb | 6 |
| Order, 40 ft stock | 10 bars | 40 ft | 400 ft | 267.2 lb | 0 |
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The takeoff says 282 ft and 188.4 lb; the order on 20 ft stock says 340 ft and 227.1 lb. That is a 20.6% gap, and it is not waste you can wish away — it is the price of buying steel in fixed lengths for a wall whose bars are 7.75 ft and 23.75 ft. When someone asks you to "just give them a number for the wall", this is the fork: the takeoff for the quote, the order for the steel, and they are 58 ft apart on a wall this size.
Which direction laps falls straight out of the bar lengths. The verticals are 7.75 ft, comfortably inside a 20 ft bar, so each one is a single piece — the verticals never lap on a normal wall. The horizontals are 23.75 ft, longer than the 20 ft bar, so every horizontal needs one lap, cut as 20 ft plus a 3.75 ft tail:
Then the twist that makes the wall its own case. Going to 40 ft stock removes all six laps, because 23.75 ft fits inside 40 ft — but each 40 ft bar carries only one 23.75 ft horizontal and throws away 16.25 ft, so the order jumps to 400 ft and the allowance to 41.8%. On this wall the lapped 20 ft stock wastes less than the lap-free 40 ft stock: 20.6% against 41.8%. Laps are not the enemy; the offcut is.
It is the same trade the footing page runs the other way round, where 40 ft stock wins because the bars there are long. The rule is not "always 40 ft" or "always 20 ft"; it is to count the pieces, not the feet, which is what the estimator page is about. And the horizontal count itself comes from the wall height, the point the spacing page makes for a slab.
A concrete block wall carries its steel the other way round from a poured wall. The horizontals are usually joint reinforcement laid in the bed joints; the load path is the verticals, cast into the grouted cores. The count runs along the length exactly like the verticals in step 1 — what changes is where the spacing comes from. It comes off the block module and the grout schedule, not from 12 to 16 in.
The rule estimators post for a quick takeoff is one vertical every 40 in:
Each vertical is a single piece, and it is as tall as the wall less top and bottom cover — the same convention step 1 used, so an 8 ft wall takes a 7.75 ft bar. The whole wall is therefore one mark, cut out of stock, and the stock length you choose decides how much of every bar is left over:
| Wall height | Bar length | Stock | Pieces per bar | Offcut per bar | Bars to order | Order length | Allowance vs net |
|---|---|---|---|---|---|---|---|
| 8 ft | 7.75 ft | 10 ft | 1 | 2.25 ft | 30 | 300 ft | 29.0% |
| 8 ft | 7.75 ft | 20 ft | 2 | 4.50 ft | 15 | 300 ft | 29.0% |
| 8 ft | 7.75 ft | 30 ft | 3 | 6.75 ft | 10 | 300 ft | 29.0% |
| 8 ft | 7.75 ft | 40 ft | 5 | 1.25 ft | 6 | 240 ft | 3.2% |
| 9 ft | 8.75 ft | 10 ft | 1 | 1.25 ft | 30 | 300 ft | 14.3% |
| 9 ft | 8.75 ft | 20 ft | 2 | 2.50 ft | 15 | 300 ft | 14.3% |
| 9 ft | 8.75 ft | 30 ft | 3 | 3.75 ft | 10 | 300 ft | 14.3% |
| 9 ft | 8.75 ft | 40 ft | 4 | 5.00 ft | 8 | 320 ft | 21.9% |
| 10 ft | 9.75 ft | 10 ft | 1 | 0.25 ft | 30 | 300 ft | 2.6% |
| 10 ft | 9.75 ft | 20 ft | 2 | 0.50 ft | 15 | 300 ft | 2.6% |
| 10 ft | 9.75 ft | 30 ft | 3 | 0.75 ft | 10 | 300 ft | 2.6% |
| 10 ft | 9.75 ft | 40 ft | 4 | 1.00 ft | 8 | 320 ft | 9.4% |
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Read the first four rows and the middle four rows together, because they say opposite things. At an 8 ft wall, 40 ft stock is the clean cut: 5 pieces per bar, only 1.25 ft left on each, so 30 verticals come off 6 bars and the allowance is 3.2% — against 29.0% on 10, 20 and 30 ft stock. At a 9 ft wall the same 40 ft stock is the worst of the four: 8.75 ft bars give 4 per bar with 5 ft cut off each one, an 8-bar order of 320 ft and a 21.9% allowance, while every other length holds 14.3%. A block wall has no stock length that is right in general. It has one that is right for its height, and it is a different one at 8 ft and at 9 ft. Stock lengths themselves are on the bar length page, and why the offcut is a remainder rather than a percentage is on the estimator page.
Count the two directions from two different dimensions. Verticals come from the wall's length: clear length ÷ vertical spacing, plus one. Horizontals come from the wall's height: clear height ÷ horizontal spacing, plus one. On this 24 ft × 8 ft wall in #4 bar at 16 in o.c. with 1.5 in cover that is 18 verticals of 7.75 ft and 6 horizontals of 23.75 ft, 282 ft as a takeoff.
One more than the number of spaces along the clear length. Clear length is 288 in minus 2 × 1.5 in = 285 in; floor(285 ÷ 16) = 17 spaces, plus a start bar = 18 verticals. Each vertical is as tall as the wall less top and bottom cover: 96 − 3 = 93 in = 7.75 ft.
Count them up the height, not along the length. Clear height is 96 in minus 2 × 1.5 in = 93 in; floor(93 ÷ 16) = 5 spaces, plus one = 6 horizontals. Each is as long as the wall less two side covers: 288 − 3 = 285 in = 23.75 ft. Getting the two dimensions the right way round is the step people get backwards.
The takeoff is net steel, the order is whole bars. The wall needs 282 ft in the ground, but bar comes in stock lengths, so the order rounds each mark up to whole bars and adds the lap where a bar is longer than stock. Here the takeoff is 282 ft and 188.4 lb; the order on 20 ft stock is 17 bars, 340 ft, 227.1 lb.
Usually not. A normal 8 or 10 ft wall gives verticals of 7.75 to 9.75 ft, well inside a 20 ft bar, so each vertical is one piece. The bars that lap in a wall are the horizontals, because a wall is normally longer than one stock bar. Only a wall taller than the stock length laps its verticals, and then one lap per vertical.
Only if the drawing calls for two mats. A single mat is centred in the wall and the counts above stand. A doubly reinforced wall carries a mat near each face, so you double both counts and add the ties or chairs that hold the two mats apart. This page works the single-mat case.
The drawing sets it; common practice is 12 to 16 in on centre both ways in a reinforced concrete wall, tightening where the wall is loaded or exposed. In a concrete block wall the verticals sit in the cores on the block module, commonly about 16 in. The spacing changes the count, not the method — the two directions are still counted from the length and the height.
Count them along the length, exactly like the verticals of a poured wall, and take the spacing off the grout schedule. The shortcut estimators post is one vertical every 40 in, or wall length (ft) ÷ 3.33 — a 100 ft block wall is 100 ÷ 3.33 = 30.03, so 30 verticals. Each one is a single piece as tall as the wall less cover, so an 8 ft wall takes a 7.75 ft bar and the whole job is one mark cut out of stock. That is where the stock length bites: on that 100 ft wall, 10, 20 and 30 ft stock all come to a 29.0% allowance for offcut while 40 ft stock comes to 3.2%, and on a 9 ft wall the same 40 ft stock is the worst of the four at 21.9%.