Construction glossary · Concrete and masonry

What is concrete coverin construction?

Concrete cover is the clear distance between the surface of embedded reinforcing steel and the nearest outside face of the concrete. It protects rebar from corrosion and fire, and ACI 318 sets it by exposure: 3 in for concrete cast against earth, 2 in for formed concrete exposed to weather or earth, and as little as 3/4 in for interior slabs. For estimators, cover sets bar lengths, chair heights, and accessory counts in every rebar takeoff.

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Updated June 2026 · Reviewed by the Ruh construction team

Protects rebar from corrosionCast against earth 3 in minSlab interior ~3/4 to 1.5 in

Concrete cover over rebar

The definition

Concrete cover, explained.

Concrete cover (drawings may call it clear cover or rebar cover) is specified by the structural engineer and shows up in three places: the cover schedule in the structural general notes, the typical details, and spec section 03 20 00 for concrete reinforcing. The values trace back to ACI 318 and step down by exposure: 3 in where concrete is cast directly against earth, 2 in for formed surfaces exposed to weather or earth, 1-1/2 in for interior beams and columns, and 3/4 in for interior slabs and walls. The detailer applies cover in shop drawings, rodbusters hold it with chairs and dobies, and the special inspector verifies it before each pour. For the estimator, cover drives bar lengths, support heights, and accessory counts. New estimators trip in two spots: they compute bar lengths from plan dimensions without deducting cover, which overstates tonnage on short bars, and they leave chairs, bolsters, dobies, and the labor to set them out of the bid entirely. Also watch for mixed cover on one element, since a footing can carry 3 in bottom cover with 2 in formed side cover.

How it is measured

Cover is a clear dimension in inches, measured from the outermost steel surface (the stirrup or tie, not the main bar) to the nearest concrete face; metric jobs show it in mm. You will find it as a cover schedule in the structural general notes, keyed to exposure condition, and repeated on typical sections. Estimators never take off cover as its own quantity; they apply it three ways. Deduct it from member dimensions to compute bar lengths, use it to pick support heights (3 in bottom cover means 3 in chairs or dobies), and count the supports themselves, typically slab bolsters by the linear foot and individual chairs by the each, spaced about 3 ft to 4 ft on center under mats.

Worked example

A worked concrete cover example.

Worked example

Take an 8 ft by 8 ft by 18 in spread footing with a bottom mat of No. 6 bars at 9 in on center each way, cast against earth, so ACI 318 requires 3 in cover. Bar length: 96 in minus 3 in cover at each end = 90 in, or 7 ft 6 in per bar. Bar count each way: 90 in / 9 in spacing + 1 = 11 bars, so 22 bars per footing. Weight: 22 bars x 7.5 ft x 1.502 lb per ft = about 248 lb. At an illustrative $1.40 per lb furnished and installed, the mat runs about $347. Holding that 3 in cover takes 3 in high chairs or precast dobies in roughly a 3 by 3 grid, so carry 9 supports per footing. If the sides were formed instead of trenched, side cover drops to 2 in and each bar picks up 2 in of length.

How Ruh handles it

How Ruh handles concrete cover.

Ruh reads the cover schedule in the structural general notes along with the footing and slab details, then applies those cover deductions automatically when it computes bar lengths, support heights, and accessory counts during the rebar takeoff. It prices the resulting tonnage and chair or dobie quantities against the contractor's own price book and hands the estimator a line-item draft that shows the cover assumptions by element. The estimator reviews those assumptions, adjusts where the engineer's notes exceed the code minimums, and signs off.

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Concrete cover: frequently asked questions

Why do footings need 3 in of concrete cover?+

The bottom of a footing is cast directly against soil with no formwork, so the surface is irregular and the steel sits in permanent ground moisture, which ACI 318 treats as the harshest exposure condition. If the footing sides are formed rather than trenched, side cover can drop to 2 in even while the bottom stays at 3 in. That distinction changes bar lengths and dobie heights, so check the foundation details before pricing.

Is concrete cover measured to the main bars or to the stirrups and ties?+

Cover is measured to the outermost steel, so in beams and columns that means the face of the stirrup or tie, not the longitudinal bar. The main bars end up sitting the cover plus one stirrup diameter from the concrete face. Detailers handle this in shop drawings, but an estimator who misses it will pick chair heights or bar lengths slightly wrong on cast-in-place beams and columns.

What happens if rebar does not have enough cover?+

Moisture and chlorides reach the steel sooner, the bar corrodes, and the expanding rust spalls the concrete surface, which is why special inspectors check cover before every placement on commercial work. Shallow cover also reduces fire resistance and bond strength. A failed cover inspection means re-chairing and re-tying steel on labor the bid never carried, so the modest cost of chairs and dobies on a typical foundation package is cheap insurance.

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What is concrete coverin construction?

Concrete cover, explained.

A worked concrete cover example.

Worked example

How Ruh handles concrete cover.

Concrete cover: frequently asked questions

Related terms

Knowing what concrete cover means is the easy half.

Try Ruh on a bid you are pricing now.

Put your next takeoff on Ruh.