Rebar Calculator: Bars, Sticks, Laps and Weight
Work out the rebar for a slab or footing: bars each way from the spacing, total length, 20 ft sticks with lap splices, weight by bar size and cost. Enter a slab or a strip footing, the on-center spacing, the edge cover and the bar size from #3 to #8, and get the bars each way, the 20, 40 or 60 ft sticks to order with the laps, the weight in pounds and tons, chairs and the cost.
Your numbers
On center, from the drawings. Treated as a maximum: the bars are spread evenly.
Concrete between the bar ends and the edge. ACI 318 asks for 3 in where concrete is cast against and permanently in contact with the ground.
The length the supplier sells.
40 bar diameters is a common rule of thumb, not a code value. ACI 318 and your drawings set the lap; type theirs.
From the drawings or your crew's practice, to estimate the chairs.
Sticks to buy
–
- Bars running the length
- –
- Bars running the width
- –
- Lap splice
- –
- Total length with laps
- –
- Fewest sticks if every offcut is used
- –
- Weight in place
- –
- Weight of the sticks
- –
- Rebar cost
- –
Offcuts are not carried from one bar to the next, so the stick count is on the safe side. Hooks, bends, dowels and corner bars are not included; add them from the drawings.
The calculation runs in your browser and ParrotNotes does not store your numbers. They sit in the page address so you can bookmark or share the result.
How to use the rebar calculator
Pick a slab or a strip footing and enter its length and width in feet. For a slab, enter the on-center spacing of the bars that run the length and of those that run the width; they are often the same. For a strip footing, enter how many continuous bars run along it and, if it has them, the spacing of the short cross bars. Then set the edge cover, the bar size and the stock length.
Worked example: a 20 × 20 ft slab with 3 in cover and #4 at 12 in each way. The bars fill 240 − 2 × 3 = 234 in, so 234 ÷ 12 = 19.5 spaces, rounded up to 20, which takes 21 bars. Each is 19.5 ft long, so one fits on a 20 ft stick: 21 sticks each way, 42 in all. That is 819 ft of #4, 547.1 lb in place, and the 42 sticks weigh 561.1 lb, or 0.28 tons.
Sticks, laps and offcuts
When a bar is longer than the stock, two sticks overlap by the lap length. With a lap of L and sticks of S, every extra stick adds S − L of length, so a bar needs (bar length − S) ÷ (S − L) splices, rounded up. On a 30 × 20 ft slab, the 29.5 ft bars need one splice each: with a 20 in lap, each bar is 29.5 + 1.67 = 31.17 ft of steel, one full stick and an 11.17 ft end piece.
End pieces and short bars are cut as many to a stick as fit, and offcuts are not carried from one bar to another, so the stick count is on the safe side. The result also shows the fewest sticks you would need if every offcut were used: total length ÷ stock length, rounded up. For the 30 × 20 ft slab that is 73 sticks on the safe side and 63 at the very least. The real number depends on the cut list, and 40 or 60 ft stock can cut the splices out.
Bar sizes and weights
US rebar is numbered by its diameter in eighths of an inch. The ASTM A615 nominal values: #3 is 0.375 in and 0.376 lb/ft, #4 0.500 in and 0.668 lb/ft, #5 0.625 in and 1.043 lb/ft, #6 0.750 in and 1.502 lb/ft, #7 0.875 in and 2.044 lb/ft, and #8 1.000 in and 2.670 lb/ft. Weight in place is the total length with the laps × lb/ft; the weight of the sticks is what you order, and suppliers often price rebar by the pound or the ton.
Switch the price between per stick, per lb and per ton to match the quote. The ton is the US short ton of 2,000 lb.
Strip footings
A continuous footing usually has a few long bars running its full length and, on some jobs, short bars across it. Enter the footing length and width, the number of long bars from the drawings and, if there are any, the spacing of the cross bars. A 40 ft footing 2 ft wide with three #4 bars and 3 in cover has three 39.5 ft bars, each spliced twice from 20 ft stock.
Corner bars, dowels into the wall and hooked ends are not in the count. Add them from the drawings, and put the chair spacing in if you want an estimate of the supports.
Concrete, steel and the rest of the takeoff
The Concrete Calculator works out the cubic yards and bags for the same slab or footing, and the Cubic Yard Calculator handles other shapes and materials. For plate, angle, tube or round bar that is not rebar, the Steel Weight Calculator gives the weight by shape and metal.
For estimators and concrete crews
The rebar on a bid comes from the drawings and from the site visit: the slab size, whether the GC wants #4 or #5, the spacing, the thickened edge they mention at the end. A number that only lives in your head becomes a guess on the quote or a short delivery on pour day.
Sources, each read on 2026-10-24. All results are estimates; the structural drawings decide:
More for construction and building-materials sales: Building materials sales, Construction daily report, Construction meeting minutes template.
The bar schedule starts on the site visit
Slab size, bar size, spacing and the change the GC mentions on the way out all get said out loud on site. Record the visit in ParrotNotes and get a transcript, a summary and the action items, so the takeoff matches what was agreed.
Get Started FreeRelated tools
- Concrete CalculatorWork out the concrete for a slab, footing, column or steps in cubic yards, the number of 60 and 80 lb bags and the cost, with a waste allowance.Open the tool
- Steel Weight CalculatorWeigh steel, stainless, aluminum and other metals as plate, sheet, bar, tube, pipe or angle, per foot or meter, per piece and for the order.Open the tool
- Cubic Yard CalculatorWork out cubic yards of topsoil, mulch, gravel, sand or concrete for any area and depth, with tons, bags and cost, and convert yards to tons.Open the tool
- Square Footage CalculatorWork out square footage for rectangles, L-shaped rooms, triangles and circles, add rooms together, and convert to square yards, square meters and acres.Open the tool