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🔩 Rebar Calculator
Calculate the quantity of rebar needed for a concrete slab based on dimensions and spacing.
How to Calculate Rebar for a Concrete Slab
Rebar is laid in a grid pattern within concrete slabs for reinforcement. To calculate the number of bars, divide the slab dimension perpendicular to the bar direction by the spacing and add 1. Repeat for both directions. Common spacing is 12 or 18 inches on center. Standard rebar comes in 20-foot lengths.
Rebar Sizes and Weights
#3 rebar (3/8″) weighs 0.376 lb/ft, #4 (1/2″) weighs 0.668 lb/ft, #5 (5/8″) weighs 1.043 lb/ft, and #6 (3/4″) weighs 1.502 lb/ft. For residential slabs, #4 rebar at 12″ spacing is most common.
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