Rebar Calculator
The Rebar Calculator estimates how much reinforcing bar you need for a simple perpendicular grid pattern in a concrete slab, based on your slab size and bar spacing. Works in U.S. or metric units. Because the bar count always rounds the span-to-spacing ratio up before adding the edge bar (ceil(span ÷ spacing) + 1), your actual on-center spacing ends up slightly tighter than the value you typed whenever the span isn't an exact multiple of the spacing — a 22 ft slab on a 12 inch grid still returns 23 bars, not 22.5, because a bar sits at every interval boundary including both edges. The tool models a single flat mat of rebar only; slabs specified with top-and-bottom reinforcement (common for structural or heavily-loaded slabs) need this total doubled, and nothing here accounts for chairs, tie wire, or the concrete cover those chairs create.
Switch between U.S. Customary and Metric units.
How This Tool Works
Pick your units, then enter your slab's length and width, your rebar grid spacing, and standard stick length to calculate total linear length and sticks needed.
Formula & Method
Bars in each direction = (span ÷ spacing) + 1. Total length = (bars one way × length) + (bars the other way × width). Sticks = total length ÷ stick length (usually 20 ft / 6 m). Enter slab size in feet with spacing in inches, or in meters with spacing in centimeters.
Example Calculation
A 20 ft long, 10 ft wide slab on a 12 inch grid, with 20 ft sticks: bars running lengthwise = ceil((10 × 12) ÷ 12) + 1 = ceil(10) + 1 = 11. Bars running widthwise = ceil((20 × 12) ÷ 12) + 1 = ceil(20) + 1 = 21. Total linear feet = (11 × 20) + (21 × 10) = 220 + 210 = 430 ft. Sticks = ceil(430 ÷ 20) = ceil(21.5) = 22 sticks.
Frequently Asked Questions
What rebar spacing is standard for slabs?+
Residential slabs commonly use 12–18 inch (30–45 cm) grid spacing, while structural or high-load slabs may require tighter spacing per an engineer's specification.
Can I calculate rebar in meters?+
Yes — switch the unit toggle to Metric and enter your slab in meters with spacing in centimeters and stick length in meters. The total is returned in linear meters.
Does this account for overlap between sticks?+
No, this gives the base linear length needed. Add roughly 40 bar diameters of overlap at every splice as recommended by your local code or engineer.
Should a structural engineer review my rebar plan?+
For any load-bearing or structural slab, always have a qualified engineer specify rebar size, spacing, and placement — this tool is for general planning only.
Does this include a top and bottom mat of rebar?+
No — it estimates a single flat grid only. If your engineer specifies reinforcement in both the top and bottom of the slab, which is common for structural or heavily loaded slabs, double the total linear length and stick count this tool returns.
Why does a 22 ft slab need 23 bars instead of 22 on a 1 foot grid?+
The formula always adds one more bar than the number of full spacing intervals, because a bar sits at each edge of the slab in addition to every interior grid line. A 22 ft span split into 22 one-foot intervals has 23 interval boundaries, so it needs 23 bars in that direction, not 22.
Found this useful? Share it
Help someone else out — or link to it from your own site.
Link to this tool
Writing about rebar calculator? Paste this on your site to link here.
<a href="https://everyfix.net/tools/rebar-calculator/">Rebar Calculator</a> by <a href="https://everyfix.net">EveryFix</a>Related Tools
Concrete Calculator
Calculate cubic yards, cubic meters, and bags of concrete for slabs, footings, and pads.
Use tool →
Cubic Yard Calculator
Convert length, width, and height into cubic yards or cubic meters for any bulk material.
Use tool →
Brick Calculator
Calculate how many bricks you need for a wall.
Use tool →
Lumber Board Feet Calculator
Calculate board feet (or timber volume) for lumber pricing and ordering.
Use tool →