Rebar Calculator

Estimate material for a rectangular rebar grid

Enter rectangle dimensions, spacing already selected for the project, stock-bar length, and an extra allowance. The result counts grid lines in both directions, totals their length, applies the allowance, and rounds stock bars up.

What this quantity estimate counts

A bar is placed at each outer edge, then additional parallel lines are counted so the gap does not exceed the entered spacing. Bars running lengthwise are positioned across the width; bars running widthwise are positioned across the length. This distinction matters when the rectangle is not square.

Calculation method

Each line count is the ceiling of the perpendicular dimension in inches divided by spacing, plus one edge line. Total line length is the lengthwise count times area length plus the widthwise count times area width. The stock quantity is the adjusted line length divided by stock length, rounded up.

Worked example

For a 20-by-12-foot rectangle at 18-inch spacing, nine bars run the 20-foot direction and fifteen run the 12-foot direction. That is 360 linear feet before allowance. With 10 percent extra and 20-foot stock, 396 feet becomes 20 whole stock bars.

Allow for layout and purchasing

The extra percentage is a planning buffer, not a designed lap length. Real cuts, laps, hooks, supports, edge clearances, openings, irregular outlines, bar availability, and supplier bundle quantities change purchasing needs. Make a layout or takeoff before ordering.

Spacing is a project input

This page does not choose bar size or spacing. Those decisions depend on loads, soil, concrete section, exposure, joints, local code, and engineered details. Use approved drawings or qualified direction. Never treat a material estimate as structural design.

Limitations and privacy

The model is one complete rectangular, two-direction grid with no deductions. It does not calculate weight, chairs, ties, dowels, development length, splice locations, reinforcement ratios, cost, or code compliance. Values stay in this browser and are not uploaded.