Question 1

What size rebar for a concrete slab?

Accepted Answer

For residential slabs 4 inches thick, #3 or #4 rebar at 12-18 inch spacing is common. For driveways and garage floors, use #4 rebar at 12-inch spacing. For structural footings, #5 or #6 rebar may be required. Always follow structural engineer specifications or local building codes.

Question 2

How far apart should rebar be spaced?

Accepted Answer

Typical spacing is 12 inches on center for slabs, 6-8 inches for footings, and per engineering for structural elements. The maximum spacing is generally the lesser of 3 times the slab thickness or 18 inches. Closer spacing provides more reinforcement.

Question 3

What is a lap splice and how long should it be?

Accepted Answer

A lap splice is where two rebar bars overlap. The minimum splice length is typically 30 to 40 times the bar diameter. For #4 rebar (1/2-inch diameter), that is 15-20 inches. For #5 rebar, 19-25 inches. In practice, 24 inches is a safe minimum for most residential work.

Question 4

How much does rebar weigh?

Accepted Answer

#3 rebar weighs 0.376 lb/ft, #4 weighs 0.668 lb/ft, #5 weighs 1.043 lb/ft, and #6 weighs 1.502 lb/ft. Standard 20-foot bars weigh 7.5 lbs (#3), 13.4 lbs (#4), 20.9 lbs (#5), and 30 lbs (#6).

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