Bars, lap splices and order weight for a continuous footing — and the stock-length decision the other tools skip
← Back to the calculatorGrid takeoff: forty 20 ft longitudinal bars at 1 in o.c. and 40 cross bars at 1.5 ft = 260 ft of #5, 271.2 lb net. Then the decision the other calculators never answer: on 20 ft stock every longitudinal bar splices once — add 40 × 25 in of lap — while 40 ft stock runs unbroken. Order weight comes out 417 lb on 40 ft stock versus 683 lb on 20 ft, for the same wall.
Open the calculator for your own dimensions, or read the three steps below.
Most tools under this phrase give you a grid count and stop: enter a length and width, get bars and weight. That is the geometry, and geometry is the easy part. A footing is then decided by two things the thin calculators never touch — how many times each bar line has to be spliced, and which stock length you order, because a 40 ft footing run does not fit in a 20 ft bar and the leftover is not a percentage you can plan away.
This page works a continuous strip footing in three steps and shows every number, so you can check it against your own drawings.
A continuous footing has bars running two ways and they are not counted the same. The longitudinal bars run the full length of the run; the transverse cross bars are spaced along it. Work in clear distances: the first and last bar sit one cover in from the ends.
For a 40 ft run, 24 in wide, #5 longitudinal bars at 1 in on centre, #5 cross bars at 12 in o.c. and 3 in clear cover (earth contact):
Two of those lines are the tension bars that carry the wall load and the other four are the distribution and dowel detail the drawings call out; the exact count and position come from the engineer. What matters for the material takeoff is that the count comes out in lines, each of which has to fit a stock bar.
Here is the gap. No mainstream rebar calculator tells you how to choose the stock length, and the ones that mention stock lengths only list them. The choice is decided by how your bar lines divide into the stock bar, and it trades material against splices on the same job.
Straight bar for the North American market comes in a small set of standard lengths. The 20 ft bar is the length you load and go with from a retail yard; 30 ft, 40 ft and 60 ft are mill and full lengths, and the long ones are limited by what a flatbed can legally carry. The practical rule for a footing is: choose the stock length that divides each bar line into whole bars with the least offcut, then count the splices it forces and price the labor against the steel.
| Bar line length | On 20 ft stock | On 40 ft stock | Which wins |
|---|---|---|---|
| 10 ft | 1 bar, 10 ft offcut | 1 bar, 30 ft offcut | 20 ft by a mile |
| 20 ft | 1 bar, no offcut | 1 bar, 20 ft offcut | 20 ft |
| 30 ft | 2 bars, 10 ft offcut | 1 bar, 10 ft offcut | 40 ft on material and splices |
| 40 ft | 2 bars, no offcut, 1 splice | 1 bar, no offcut, 0 splices | 20 ft on material, 40 ft on splices |
| 60 ft | 3 bars, no offcut, 2 splices | 2 bars, 20 ft offcut, 1 splice | 20 ft on material, 40 ft on splices |
| 80 ft | 4 bars, no offcut, 3 splices | 2 bars, no offcut, 1 splice | 20 ft on material, 40 ft on splices |
Swipe the table sideways for more columns →
Read the table as two columns of cost, not one. Material is the length you buy, and 20 ft stock wins it whenever the line divides evenly into 20 ft — which for a footing run of a whole number of 20 ft bays it usually does. Splices are the labor: every piece boundary is a lap to place, tie and inspect, and 40 ft stock halves the piece count on any line over 40 ft. The trap is the 30 ft line, which divides evenly into neither stock length and wastes 10 ft on both — there 40 ft at least saves the splice.
A bar line longer than one stock bar has to be spliced, and the splice adds a lap length to that line. For tension laps in a footing the field rule is 40 × the bar diameter, which is the basis of a Class B splice:
On our 40 ft footing run with 20 ft stock, every one of the twenty longitudinal bars splits into two pieces and takes one splice of 25 in. The forty cross bars are only 1.5 ft long and come out of three separate 20 ft bars, so they need no splice at all:
Then the order. Divide each line length by the stock length, round up to whole bars, count every line:
| Item | Working | 20 ft stock | 40 ft stock |
|---|---|---|---|
| Longitudinal bars (40 ft each) | 20 bars | 20 × 2 = 40 bars of 20 ft | 20 bars of 40 ft |
| Bar for the longitudinal lines | whole bars | 40 × 20 = 800 ft | 20 × 40 = 800 ft |
| Cross bars (1.5 ft each) | 40 bars, 60 ft | 3 extra 20 ft bars | 2 extra 40 ft bars |
| Lap splices, longitudinal | 1 per bar at 20 ft stock | 20 | 0 |
| Laps to make good | 40 × db rule | 20 laps × 25 in | none |
| Bars bought | whole bars | 43 | 22 |
| Order weight | bars × stock × lb/ft | 897 lb | 918 lb |
Swipe the table sideways for more columns →
Read the last two rows together, because that is the real trade and it is not a simple price call. The 20 ft order buys 41 fewer feet of bar (860 ft against 880 ft), because forty 20 ft bars cover the 800 ft of longitudinal line exactly with nothing left over, and the 60 ft of cross bar then comes out of three cheap 20 ft bars. What it buys that saving with is 20 lap splices, one in every longitudinal bar. The 40 ft order has no splices at all, but it pays for that by buying two 40 ft bars for the 60 ft of cross bar, and the second one is mostly offcut. The estimator page works that arithmetic in full.
Lap length is not an independent number; it is tied to development length. Where a bar has to transfer force to the next bar, the splice has to be long enough for the force to move across, so the lap is built from the bar's development length times a class factor: Class A is 1.0 × ld, Class B is 1.3 × ld.
The 40 × db rule is a field shorthand that lands close to the code value for ordinary footing bars. Where the drawings specify a class or a computed lap length, use that value — a Class A splice in the same bar saves nearly a third of the lap.
The development length page works the full six-step calculation for a #8 bar and gives the tables for #3 to #11.
Work two directions. The longitudinal bars run the full length of the footing, so their count is the number of lines the drawings stack across the width, and each one is as long as the run. The transverse cross bars are spaced along the run: divide the clear length by the spacing, round down, add one, and multiply by the width less two covers. Our 40 ft run of 24 in wide footing with #5 bars at 1 in o.c. longitudinally and #5 cross bars at 12 in o.c. gives 800 ft of longitudinal bar plus 40 cross bars at 1.5 ft, or 60 ft — 860 ft in all, 897 lb of #5.
It is decided by how the bar lines divide into the stock length. Divide each line length by the stock length and round up to a whole bar; whatever is left is offcut, and you cannot use a percentage of it. A 40 ft run takes two 20 ft bars per line with no offcut, or one 40 ft bar with no offcut — both work, but the 20 ft pair needs a splice and the single 40 ft bar does not. A 30 ft run takes one and a half 20 ft bars, so you buy two and discard 10 ft of every line, and there 40 ft stock wins outright. On our 40 ft footing the 20 ft order is 43 bars or 897 lb with 20 lap splices, and the 40 ft order is 22 bars or 918 lb with none — the short bar buys 41 ft less steel, the long bar needs 20 fewer laps.
For an ordinary tension lap in a footing the field rule is 40 times the bar diameter: 20 in for a #4, 25 in for a #5, 30 in for a #6, 40 in for a #8. That rule is the basis of a Class B splice. If the drawings specify a class, use the drawing value, because Class A is 1.0 times the development length and Class B is 1.3 times it.
Three inches of clear cover for all bar sizes where concrete is cast against and permanently in contact with earth, per ACI 318-19 Table 20.6.1.3.1. That is the governing case for a footing, and it is larger than the interior slab value of 3/4 in, which is why footing bars sit deeper and their chairs are taller.
A continuous wall footing uses longitudinal bars along the run for bending and transverse bars to distribute load and hold the cage. A spread or pad footing under a column is reinforced in both directions as a mat, because it bends two ways. Bar size, spacing and direction come from the drawings; this page takes those values and finishes the material takeoff.
The count does not change, the number of pieces does. If a bar line is longer than one stock bar it has to be spliced, and each splice adds a lap to that line. A 40 ft run on 20 ft stock breaks every longitudinal bar into two pieces with one splice of 25 in for #5 bars, so each of the twenty bars carries 25 in of extra lap — 500 in, or 41.7 ft, of extra steel across the footing. On 40 ft stock the same bars run unbroken and that lap disappears.
Work the order in whole stock bars per line and the cut waste is already accounted for — you are buying complete bars, not a length. Add a small handling allowance for cutting error and damaged ends, typically a few per cent, and treat leftover offcut as material for a shorter line rather than a planned percentage of the order.
A wall is worked the same way as a footing, only vertical. The horizontal bars run the length of the wall and are counted like the footing's longitudinal bars; the vertical bars are spaced along it and counted like the cross bars. One difference matters for the takeoff: a wall is usually taller than one stock bar, so the vertical bars splice more often, and that splice count is what drives the order weight. Measure the wall length and height in clear distances, less the cover, apply the same floor( span ÷ spacing ) + 1 rule to each direction, and add a 40 × db lap wherever a bar line crosses a stock-length boundary.