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Excel Tutorials / Concrete & Rebar Quantity Calculator in Excel
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Concrete & Rebar Quantity Calculator in Excel

10 min read · Template referenced below

Rather than calculating concrete volume and rebar quantities by hand for every slab or footing, a single Excel sheet with the right formulas can handle dozens of pours and instantly show totals for an entire project.

1
List your slab dimensions.
Create columns for Length (ft), Width (ft), and Thickness (in) — one row per slab or footing.
2
Calculate cubic yards.
=(Length*Width*(Thickness/12))/27 converts length × width × thickness in inches into cubic yards directly in one formula.
3
Estimate rebar length.
For a slab reinforced on a grid, rebar length ≈ (Length/Spacing+1)*Width + (Width/Spacing+1)*Length, where Spacing is your rebar spacing in feet (e.g. 1.5 for 18" on-center).
4
Convert rebar length to weight.
Multiply total rebar length by the unit weight for your bar size (for example, 0.668 lb/ft for a #4 bar) to get total pounds needed.
Prefer not to build the rebar weight formulas from scratch? BuildQuantify's Rebar Weight Calculator does this instantly online — useful for spot-checking your spreadsheet's output.

Once built, this sheet becomes a fast way to compare pour sizes across a whole site plan and generate a single concrete order and rebar cut list in one pass.

Worked example: a 20 ft × 12 ft slab, 6 in thick

StepCalculationResult
Concrete volume=(20*12*(6/12))/274.44 cu yd
With 10% waste=4.44*1.104.89 cu yd (order 5)
Rebar, #4 at 18 in o.c. each way=(20/1.5+1)*12+(12/1.5+1)*20352 ft
Rebar weight=352*0.668about 235 lb

In the formula the spacing is 1.5 because 18 in is 1.5 ft. Because the bar count must be a whole number, a more careful version is =(ROUNDUP(Length/Spacing,0)+1)*Width + (ROUNDUP(Width/Spacing,0)+1)*Length.

Unit weights to remember: #3 bar is 0.376 lb/ft, #4 is 0.668 lb/ft, #5 is 1.043 lb/ft and #6 is 1.502 lb/ft. Put these in a small lookup table on a second tab and use VLOOKUP so you never retype them.

What this simple sheet does not include

  • Lap splices. Bars longer than stock length (20 ft is common) need overlaps, often 40 bar diameters or more. Add a lap allowance to the length.
  • Concrete cover and chairs. Bars stop short of the slab edge by the specified cover, so the formula slightly overestimates for small slabs.
  • Bends, hooks and stirrups. Footings and beams need a proper bar schedule. This is where a dedicated tool like the Rebar Cutting and Bending page saves hours.

Frequently asked questions

How much extra concrete should I order?

Five to ten percent is typical, depending on subgrade condition, formwork tolerance and pour complexity. Always follow your supplier's guidance and the project specification.

Why divide by 27?

One cubic yard equals 27 cubic feet (3 ft × 3 ft × 3 ft), and the length, width and thickness are converted to feet first.

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