Concrete Slab Rebar Calculator

About this calculator

Rebar count for a concrete slab is found by dividing the slab's length and width by the chosen bar spacing and adding one, done separately in each direction for a grid layout, then multiplying by the number of bars needed for the total length of reinforcement. Tie wire quantity follows from the number of intersections in the grid — each crossing point needs a tie — multiplied by the length of wire used per tie.

Concrete contractors and DIY slab-pourers run this calculation before ordering rebar because reinforcement spacing directly affects a slab's crack resistance and load capacity — tighter spacing (denser grid) is used for driveways and slabs bearing vehicle loads, while wider spacing suffices for patios and light-duty slabs. Getting the bar count and tie wire estimate right avoids a mid-pour materials run, which is far more disruptive for rebar placement than for concrete itself.

This calculator takes your slab size and bar spacing, and returns the bar count, total rebar length and tie wire needed.