How many sticks of rebar does a garage slab take? The answer depends on slab size, grid spacing, and stick length. The Rebar Calculator lays out a square grid and counts the steel for you.
It helps homeowners and small contractors price a slab before a supply run. Enter the slab size in feet and the spacing in inches. Results update as you type.
Table of Contents
- What the Calculator Does
- How to Use It, Step by Step
- The Rebar Grid Formula
- Worked Example
- How to Read the Results
- Spacing, Laps, and Buying Tips
- Limitations and Assumptions
- FAQs About the Rebar Calculator
What the Calculator Does
The tool models one rectangular slab with bars running both ways at the same spacing. It returns five results.
- Rebar Sticks Required: the number of full sticks to buy. The heading follows your stick length, such as Total 10' Rebar Sticks Required.
- Total Linear Footage: the grid length plus a fixed 10% for overlap and waste.
- Total Material Cost: sticks times your price per stick.
- Tie Wire Intersections: the number of points where bars cross.
- Grid Pattern Density: your spacing shown as a grid, such as 12" x 12".
- Copy Rebar Breakdown copies a summary, and Reset restores the sample values.
How to Use It, Step by Step
- Enter Slab Length (Feet). The sample is 20 feet.
- Enter Slab Width (Feet). The sample is 15 feet.
- Enter Grid Spacing (Inches Center-to-Center). This is the distance from the middle of one bar to the next.
- Enter Single Stick Length (Feet). Many stores sell 10 foot and 20 foot sticks.
- Enter Price Per Rebar Stick ($) for the bar size you plan to buy.
- Read the stick count, then check the four cards below it.
- Press Copy Rebar Breakdown to save the list for your supplier.
The Rebar Grid Formula
The tool counts how many bars fit across each direction, then multiplies by bar length. It adds 10% and divides by stick length.
Bars Each Way × Bar Length×1.10÷Stick Length=Sticks (Rounded Up)
- Spacing in feet = spacing in inches ÷ 12.
- Bars running the length = width ÷ spacing, rounded down, plus 1.
- Bars running the width = length ÷ spacing, rounded down, plus 1.
- Grid feet = (length bars × length) + (width bars × width).
- Linear feet = grid feet × 1.10. Sticks = linear feet ÷ stick length, rounded up.
- Cost = sticks × price. Tie points = length bars × width bars.
Worked Example
Keisha is pouring a 24 by 20 foot garage slab. She plans an 18 inch grid with 20 foot sticks at $11 each.
| Step | Calculation | Result |
|---|
| Bars running 24 ft | 20 ÷ 1.5 = 13.33, down to 13, plus 1 | 14 bars |
| Bars running 20 ft | 24 ÷ 1.5 = 16, plus 1 | 17 bars |
| Grid feet | (14 × 24) + (17 × 20) | 676 ft |
| Total Linear Footage | 676 × 1.10 = 743.6 | 744 Feet |
| Sticks Required | 743.6 ÷ 20, rounded up | 38 Sticks (20' ea) |
| Total Material Cost | 38 × $11 | $418.00 |
| Tie Wire Intersections | 14 × 17 | 238 Grid Points |
If her plans call for a 12 inch grid instead, the tool shows 56 sticks. The cost rises to $616.00, with 525 grid points to tie.
How to Read the Results
Rebar Sticks Required is your shopping number. It is already rounded up to whole sticks.
Total Linear Footage includes the 10% extra, so it is longer than the bare grid. Use it to compare stick lengths or check a supplier quote.
Total Material Cost covers the bars only. Tie wire, chairs, and cutting tools are extra.
Tie Wire Intersections counts every crossing. Some crews tie each one, while others tie every second crossing.
Spacing, Laps, and Buying Tips
Closer spacing adds steel fast. In the example, an 18 to 12 inch change takes the count from 38 to 56 sticks. Rebar sizes use eighths of an inch, so #4 bar is 1/2 inch across.
When one stick is too short, bars must overlap at a lap splice. A common rule of thumb is about 40 bar diameters, or 20 inches for #4 bar. The fixed 10% may not cover many laps on a long slab.
Rebar should sit inside the concrete on supports called chairs, not on the ground. Size the pour itself with the concrete slab calculator. For footings or odd shapes, the concrete calculator works better.
A gravel base goes under most slabs, and the gravel volume calculator can size it. A driveway slab starts with the driveway area calculator. See the home and construction tools hub for more.
Limitations and Assumptions
- The tool assumes one rectangle with equal spacing both ways. It does not take a bar size.
- Bars start at the slab edge. It does not subtract edge cover, the concrete kept between steel and the form.
- The 10% overlap and waste factor is fixed and cannot be changed.
- A blank or invalid field shows a short message, and every result reads N/A until you fix it.
- Length and width run from 1 to 10,000 feet, and spacing from 4 to 36 inches. Stick length runs from 5 to 40 feet, and price must be $0 or more.
- Local building codes and an engineer or inspector decide final bar size, spacing, and laps.
FAQs About the Rebar Calculator
What rebar spacing is common for a home slab?
Many residential slabs use a grid between 12 and 18 inches. Your plans or local code set the real number.
Does the tool include lap splices?
It adds a fixed 10% for overlap and waste. It does not count each lap, so long slabs may need more.
Why does the bar count add one?
A row of bars needs one more bar than the number of gaps. Five gaps across a slab need six bars.
Can I use 10 foot sticks?
Yes. Enter 10 in the stick length field. The stick count roughly doubles, since each stick covers half the length.
Does it work for wire mesh?
No. It counts loose bars in a grid. Welded wire mesh is sold in sheets or rolls, so estimate it by area.
How much tie wire do I need?
The tool counts crossings, not wire length. Use the grid point count to plan how many ties to make.
This calculator gives planning estimates only and is not professional engineering, electrical, or building code advice. Reviewed for general accuracy by Prof. Dr. Khalil Mudassar, PhD.