How much does #4 rebar weigh per foot?

#4 rebar weighs 0.668 pounds per linear foot. It has a nominal diameter of 0.500 inches (1/2 inch) and is the most common bar size for residential slab reinforcement at 12-inch on-center spacing.

What is the lap splice length for #4 rebar?

The standard tension lap splice for #4 rebar is 18 inches per ACI 318 (Class B splice in normal-weight concrete at 3,000 PSI with uncoated bars). Always verify with your project structural drawings — higher-strength concrete or epoxy coating changes the required length.

How many #4 bars do I need for a 20x30 foot slab at 12-inch spacing?

For a 20x30 foot slab with #4 bars at 12-inch on-center both ways and 3-inch cover: you need approximately 21 bars spanning the 30-foot direction and 31 bars spanning the 20-foot direction, for a total of about 1,215 linear feet weighing approximately 812 pounds (0.406 tons).

What is the minimum concrete cover for rebar?

Per ACI 318 Table 20.6.1: 3 inches for concrete cast directly against earth (footings), 2 inches for concrete exposed to weather with #6 bars or larger, 1.5 inches for weather exposure with #5 bars or smaller, and 0.75 inches for interior concrete not exposed to weather.

Rebar Calculator

Calculate rebar quantities with bar size selection, ACI 318 concrete cover, automatic lap splices, and weight in pounds and tons. Grid, one-way, perimeter, and tie layouts.

Layout pattern

Bar Size

Concrete Cover (ACI 318)

Custom:inches

Slab Dimensions

Length (ft)

Width (ft)

Spacing X (in OC)

Spacing Y (in OC)

Waste factor3%

Standard 2-3% for simple layouts, 5% for complex. Covers cutting waste and field conditions.

Rebar Estimating Essentials

Bar Sizes and Weight

Standard deformed reinforcing bars (ASTM A615 Grade 60) range from #3 (0.375" dia, 0.376 lb/ft) to #11 (1.410" dia, 5.313 lb/ft). The bar number roughly equals the diameter in eighths of an inch — #4 is 4/8" = 0.500". Rebar is ordered by the ton (2,000 lb short ton).

Concrete Cover (ACI 318)

Concrete cover protects rebar from corrosion. ACI 318 Table 20.6.1 specifies minimum cover: 3" for concrete cast directly against earth (footings), 2" for bars exposed to weather (#6 and larger), 1.5" for weather exposure (#5 and smaller), and 0.75" for interior concrete not exposed to weather.

Lap Splices

When bar runs exceed stock length (20 ft for #3-#5, 40 ft for #6-#11), bars are overlapped at lap splices per ACI 318. Splice length depends on bar size — from 12" for #3 to 41" for #8. This calculator automatically adds splice material when bar lengths exceed stock lengths.

Waste Factors

Rebar waste comes from cutting drops, field damage, and bend allowances not captured in the linear footage calculation. Standard waste: 2-3% for simple grid layouts, 5% for complex shapes with many bends. The waste factor does not replace lap splice calculations — splices are already included in the LF total.

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