Rebar Calculator

Estimate rebar quantity, bar count, spacing, total rebar length, lap splice allowance, rebar weight, and material cost. Use this rebar calculator for concrete slabs, footings, walls, driveways, patios, foundations, grid reinforcement layouts, and preliminary concrete planning.

Calculate Rebar

Rebar count = floor(clear inside dimension ÷ spacing) + 1. Total length = bar count × bar run length + laps + waste.
Your result will appear here.

How the rebar calculator works

Clear dimensions:
The calculator subtracts edge clearance from both sides of the slab, footing, wall, or concrete area.

Bar count:
The calculator estimates how many bars fit in each direction based on spacing and clear inside dimensions.

Total length:
The calculator multiplies bar count by run length, then adds lap splices, extra bars, layers, similar areas, and waste.

Weight and cost:
The calculator uses rebar size weight per foot, cost per foot, and tie count to estimate total weight and material cost.

Why use a rebar calculator?

A rebar calculator helps estimate reinforcement quantities before buying material or preparing a concrete pour.

It can help compare bar spacing, bar count, total length, stock bar count, lap allowance, waste, tie count, rebar weight, and approximate cost.

What your result means

Your result shows estimated bars running each direction, actual spacing, total bar count, total rebar length, stock bar count, lap splice allowance, waste allowance, tie count, rebar weight, and estimated material cost. These are planning estimates only.

Rebar calculator formulas

Frequently asked questions

How do you calculate how much rebar you need?

Subtract edge clearance from the layout dimensions, divide the clear dimensions by the rebar spacing, add one bar, then multiply the bar count by the run length. Add laps, waste, layers, and extra bars as needed.

What does 18 inches on center mean?

It means the center of one rebar is spaced 18 inches from the center of the next rebar.

How much does #4 rebar weigh?

#4 rebar weighs about 0.668 pounds per linear foot. A 20-foot stick weighs about 13.36 pounds before cutting or waste.

Can this calculator replace structural reinforcement design?

No. Final rebar design should follow structural drawings, local code, concrete strength, load requirements, cover requirements, lap splice rules, soil conditions, and professional engineering when needed.