Rebar Quantity Calculator

Estimate how much rebar you need for concrete slabs, pads, and driveways. Set grid spacing, edge clearance, and waste margin for a jobsite-ready steel takeoff.

Slab Details

Slab Length

Slab Width

Rebar Grid Spacing

Rebar Clearance Edge Buffer

Waste Margin Allowance10%

0%30%

Live Results

Total 20ft Rebar Sticks Required

Total Linear Footage

209.00 ft

Grid Intersections

121

Tie wire estimate

Grid Layout

11 × 11

Rows × columns

Includes 10% waste allowance · Sticks rounded up

How to Use This Calculator

Enter slab dimensions. Measure slab length and width in feet for the area receiving rebar.
Set grid spacing. Enter bar spacing in inches — 12 in or 16 in on-center is common for residential slabs.
Add waste margin. Use 10% for rectangular slabs. Increase for lap splices, hooks, and cut waste at edges.
Review stick count and tie wire. Order 20 ft sticks based on the calculated count. Plan tie wire for each grid intersection.

Formula & Example

Rebar grid estimates start by subtracting the edge clearance buffer from each slab dimension. A typical 3-inch inset keeps bars away from form edges and allows proper concrete cover on all sides before the grid spacing math runs.

Bars running along the slab length are counted as rows; bars running along the width are counted as columns. Each direction uses the ceiling of the effective span divided by spacing, plus one bar at each edge of the grid. Total linear footage is the sum of all row lengths plus all column lengths.

Effective Length = Slab Length − (2 × Edge Buffer ÷ 12)

Effective Width = Slab Width − (2 × Edge Buffer ÷ 12)

Rows = ⌈Effective Width ÷ (Spacing ÷ 12)⌉ + 1

Columns = ⌈Effective Length ÷ (Spacing ÷ 12)⌉ + 1

Total Linear Footage = (Rows × Effective Length) + (Columns × Effective Width)

20 ft Sticks = ⌈Total Linear Footage ÷ 20⌉ × (1 + Waste % ÷ 100)

Grid intersections (rows × columns) give a quick tie-wire count for securing the mat before the pour. A waste margin on stick count covers cutoffs, lap splices, and bent bars that cannot be reused.

Standard Rebar Size Dimensions

Bar Size	Diameter	Common Use
#3	3/8 in (0.375 in)	Light residential slabs, walkways
#4	1/2 in (0.500 in)	Standard residential driveways & slabs
#5	5/8 in (0.625 in)	Heavy-duty pads, commercial slabs

Worked Example

A 20×20 ft slab with #4 rebar at 16 in OC each way: ~16 bars per direction × 20 ft = 320 ft per direction × 2 = 640 ft total. At 20 ft sticks: 32 sticks before waste.

Frequently Asked Questions

How much rebar do I need for a 10×10 concrete slab?▾

A 10 ft × 10 ft slab with 12-inch grid spacing and a 3-inch edge buffer yields roughly 209 linear feet of rebar — about 11 twenty-foot sticks before waste. With a 10% waste allowance, order 13 sticks. At 18-inch spacing the same slab needs about 9 sticks; at 24-inch spacing, roughly 7 sticks. Always confirm bar size and spacing with your local building code.

What rebar spacing is required for a concrete slab?▾

Residential slabs typically use #3 or #4 rebar at 12 to 18 inches on-center in both directions. Light walkways and shed pads may allow 18-inch or 24-inch spacing. Driveways and garage floors often require 12-inch spacing with #4 bar. Commercial and heavy-load pads may call for #5 bar at tighter spacing — check your jurisdiction's adopted building code before ordering steel.

How many 20-foot rebar sticks do I need for a driveway?▾

For a typical 20 ft × 12 ft residential driveway at 12-inch spacing with 3-inch edge clearance, expect roughly 495 linear feet of rebar — about 25 twenty-foot sticks before waste (28 with 10% waste). Add extra margin for lap splices at joints and cutoffs at the form edges. Use this calculator with your exact dimensions and spacing to get a stick count tailored to your pour.

What rebar spacing is required for a residential slab?▾

Many residential slabs use #3 or #4 rebar at 12–18 in on-center each way, or 6×6 W1.4×W1.4 welded wire mesh. Check local code and engineer specs — garages and driveways often require tighter spacing.

How much overlap do rebar splices need?▾

Standard lap splice length is 40 bar diameters — about 12 in for #3 bar and 16 in for #4 bar. Add overlap length to your linear footage calculation or increase waste margin to cover splices.

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