How Much Rebar Do I Need for Footings?
A footing is a long, narrow rebar grid: a few continuous bars running its length plus transverse ties at a spacing. Here is how to count both, allow for the lap splices the long runs need, and turn it into linear feet and bars to buy.
By the Calculate My Reno Team / Published
Skip to the tool
Open the Reinforcing Bar (Rebar) Calculator
A footing is just a long, narrow rebar cage: a few longitudinal bars (the ones running the full length) plus stirrups - small closed loops of bar spaced along it that hold the long bars in place. The longitudinal bars do the structural work and almost always need lap splices (overlapped joints), because a footing is longer than a single stock bar.
A footing holds up the building, so it is more structural than a slab. Use the size, bar count and spacing from your engineer or local code - if you do not have those, that is a sign to get them before you pour. New to the words here? The rebar glossary covers cover, lap splice and stock bar.
Skip the math
Switch the rebar calculator to footing / cage mode and enter the footing length, width, depth, the number of longitudinal bars and the stirrup spacing. It splices the long bars, sizes each bent stirrup, and gives the linear feet, weight and stock bars to buy - not a flat-mat approximation.
How a footing differs from a slab
A slab is a flat mat; a footing is a 3D cage, so the two are counted differently:
- The longitudinal bars run the length, top and bottom, and carry the lap splices because the footing is longer than a stock bar.
- The stirrups (also called links) are closed loops of bar wrapping the cage every so often. Each loop is as long as the way around the cross-section (measured in at the cover), plus a bit extra for the bent hooks at the ends.
longitudinal length = bars × (length − 2 × cover) + laps
stirrup count = (length − 2 × cover) ÷ stirrup spacing, rounded DOWN, then + 1
stirrup length each = 2 × ((width − 2 × cover) + (depth − 2 × cover)) + hooks
total = (longitudinal length + stirrup count × stirrup length) × waste
In words: the long bars run the whole length (spliced where they join), and you fit one stirrup every “stirrup spacing” along that length, each one looping around the footing’s cross-section.
Worked example
A 40 ft × 1.5 ft wide × 1.25 ft deep strip footing, 3 in cover, 4 longitudinal #4 bars, stirrups every 8 in, 20 ft sticks, 5% waste. (3 in of cover each side is 0.5 ft, and 8 in spacing is 0.67 ft.)
- Longitudinal: 4 bars of (40 − 0.5) = 39.5 ft. Each 39.5 ft run is longer than a 20 ft stick, so it needs one lap join (≈ 1.7 ft of overlap for #4 bar): 4 × 41.2 ≈ 165 ft.
- Stirrups: (40 − 0.5) ÷ 0.67 = 59, round down, + 1 = 60 stirrups. Each loop is 2 × ((1.5 − 0.5) + (1.25 − 0.5)) + 0.5 ft for hooks ≈ 4 ft, so 60 × 4 = 240 ft.
- Total: (165 + 240) × 1.05 ≈ 425 ft - about 22 sticks of 20 ft bar, roughly 285 lb of #4.
For the general method see how much rebar do I need; for flat slabs see how much rebar for a slab.
Tips for footing reinforcement
- Stagger the lap splices so they are not all at the same cross-section.
- Keep the longitudinal bars at the right cover off the bottom and sides on chairs and spacers.
- Hook or bend the bars at corners and intersections per your detail so the footing acts as one.
- The number of bars, size and cover come from your engineer or local code - this guide sizes the quantity only.
Frequently asked questions
How much rebar do I need for footings?
Use the rebar calculator in footing / cage mode. Count the continuous longitudinal bars running the footing length (often 2 to 4, set by your design) plus the closed stirrups at a spacing, then add a lap splice for each joint the long runs need. A 40 ft strip footing with 4 longitudinal #4 bars is about 165 ft of longitudinal steel with laps, plus the stirrups. The calculator works it all out from the footing length, width, depth and stirrup spacing.
How many rebar in a footing?
It is set by the design, but a typical residential strip footing runs 2 to 4 continuous longitudinal bars near the bottom, with transverse ties every 12 to 24 in. A wider or more heavily loaded footing carries more longitudinal bars and sometimes a top layer too. Enter the footing width and your spacing and the calculator counts both directions.
What size rebar for footings?
#4 or #5 (12 mm or 16 mm) bar is common for residential footings, with the exact size, number of bars and spacing set by your engineer or local code. Bigger or more heavily loaded footings step up in size or add bars. Set the size in the calculator to get the weight and the bars to buy.
Do footing bars need lap splices?
Almost always - footings are usually longer than a stock bar, so the continuous longitudinal bars are spliced by overlapping two bars by a lap length (about 40 bar diameters is a common starting figure, but follow your code). Stagger the splices so they do not all land at the same point. The calculator adds one lap per joint to the length and the bar count.
How much rebar for a 40 foot footing?
A 40 ft footing with 3 continuous longitudinal bars is about 120 ft of longitudinal steel, plus a lap splice on each run (a 40 ft run in 20 ft sticks needs one splice each), plus the transverse ties. That is roughly 130 to 140 ft of bar before the ties and waste. The calculator handles the laps and the tie count.