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Rebar Calculator

Count the bars each way in a slab from its size, spacing and cover, then get the laps, the stock bars to buy and the total steel weight.

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Rebar Calculator is free to use as often as you like, directly from this page. It sits under Building & renovation in our catalogue, alongside Beam Load Calculator and Board Foot Calculator.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What does Rebar Calculator do?

Count the bars each way in a slab from its size, spacing and cover, then get the laps, the stock bars to buy and the total steel weight.

When would I actually use this?

Buying the right amount at the merchant: how many tiles, how much paint, how many bags of concrete, and what it all comes to.

What is the most common mistake?

Ordering the exact calculated quantity. Every material loses some of itself between the pallet and the finished job — offcuts, breakage, a bag that sets, a coat that soaks in further than the datasheet says — so add the allowance yours asks for, and order it in one delivery: a second batch rarely matches the first.

Is there a tool for the next step?

Board Foot Calculator is the closest one after this: Work out board feet from thickness, width and length, with quarter notation, metric entry, 30 wood species, moisture content and price.

What else is worth having open alongside it?

Bolt Torque Calculator and Carpet Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

The geometry is exact for the dimensions you enter. Coverage rates come from manufacturer datasheets and vary with the surface, the number of coats and how absorbent the substrate is.

Further reading

All guides →
GuideHow Much Rebar a Slab or Wall Needs — Bars, Laps and CoverBars each way, splice lengths in bar diameters, cover from the edge, and the exact tonnage to order. Run against the calculator, including the two places where its bar count comes out short.GuideWhat a Steel Plate, Bar or Tube Weighs — And What the Number Is ForSection area times length times density, for nine profiles and fourteen metals. What the calculator returns, why one figure covers every carbon-steel grade, and the two places its geometry is not the merchant's geometry.GuideMaterials for a Retaining Wall — And the Thing That Actually Makes Them Fall OverBlocks, base gravel, drainage stone, geogrid and pipe, counted from the calculator's own output. Then the number nobody puts in a materials list: a saturated backfill pushes about 2.2 times as hard as a drained one.GuideEstimating a Beam's Safe Load: Span, Deflection and the Load CaseA calculator gives you an order of magnitude, and anything holding up a floor, a roof or people needs an engineer and a code check. Between those two facts there is a great deal worth knowing: which power of the span the deflection really follows, which loading case the tool assumes, and what L/360 is in fractions of an inch on a span you can measure.ExplainerTightening a Bolt to the Right Torque: Why the Number on the Wrench Is a GuessTorque does not hold a joint together — preload does, and torque is a poor proxy for it. Here is where 90 % of your effort goes, what the K-factor really is, and why the same 37.84 N·m gives anything from 12.61 kN to 37.84 kN of clamping force.GuideHow Much Lumber a Project Needs — And Why a 2×4 Isn't OneCount pieces first, then linear feet, then board feet. A 2×4 measures 1½ × 3½ inches but is billed on the full 2 × 4 — 34 % of what you pay for is sawdust. Worked from the calculator's real output, with the waste rule it actually applies.