Size and schedule your concrete reinforcement

For a standard 4-inch residential slab (patio, walkway), #3 bars at 18-inch spacing or #4 bars at 18-inch spacing are typical. For driveways and garage floors that carry vehicle loads, #4 bars at 12–16 inch spacing is the standard. Structural slabs, foundations, and anything engineer-specified may call for #5 or larger. Use the rebar calculator to get the exact bar count and footage for your slab dimensions.

Concrete cover is the minimum thickness of concrete between the outer surface and the nearest rebar. It protects steel from corrosion and fire. ACI 318 sets minimum cover at 3 inches for concrete cast against earth, 1.5 inches for exposed concrete, and 0.75 inches for interior slabs not exposed to weather. Insufficient cover is one of the leading causes of premature rebar corrosion and spalling. Use the cover calculator to verify your required depth by exposure class and element type.

Rebar weight is calculated as: total linear feet × unit weight per foot for the bar size. For example, #4 rebar weighs 0.668 lbs per linear foot. 500 linear feet of #4 = 334 lbs. Always add 10% for lap splices, cuts, and waste. The rebar weight calculator handles all standard bar sizes (#3 through #11) and outputs both lbs and kg, matching the format most steel suppliers use for quoting.

For light-duty slabs — sidewalks, patios, and residential walkways — welded wire mesh (WWM) is an acceptable substitute for rebar and is easier to install. The standard specification is 6×6-W1.4/W1.4. For driveways, garage floors, and any slab carrying vehicle loads, rebar is strongly preferred because it provides superior crack control and is easier to position at the correct height. For structural elements — footings, columns, beams — rebar is required and wire mesh is not a substitute.

ACI 318 sets minimum clear spacing between parallel bars at the greater of: 1 inch, 1.33 times the maximum aggregate size, or the bar diameter. In practice, this means bars should never be closer than 1 inch clear in most residential mixes. Maximum spacing for temperature and shrinkage reinforcement is 5 times the slab thickness or 18 inches — whichever is less. The rebar calculator enforces ACI 318 spacing limits automatically and flags if your inputs fall outside code requirements.