Primary material
9 sticks
Rebar sticks
Use the stick count as a buying starting point, then confirm the bar size (#3/#4/#5), grade, and stock length with the store.
Rebar calculator
Rebar calculator for a concrete slab grid.
Enter the slab size, grid spacing, and bar size to estimate the number of bars, total linear feet with lap overlap, 20 ft sticks, steel weight, and material cost.
10 x 10 slab, 16 in grid
9 sticks
112 lb of #4 steel
Formula
span / spacing + 1
both directions, plus overlap
Best for
Slab mats
Patios, driveways, shed pads
Quick reference
Rebar for common slab sizes
#4 bar in a 16 in grid with 3 in edge clearance and 10% for lap splices, bought as 20 ft sticks.
| Slab size | Bars each way | Linear feet | 20 ft sticks | Steel weight |
|---|---|---|---|---|
| 10 x 10 ft | 8 + 8 | 167 ft | 9 | 112 lb |
| 12 x 12 ft | 9 + 9 | 228 ft | 12 | 152 lb |
| 16 x 20 ft | 12 + 15 | 513 ft | 26 | 343 lb |
| 20 x 20 ft | 15 + 15 | 644 ft | 33 | 430 lb |
| 24 x 24 ft | 18 + 18 | 931 ft | 47 | 622 lb |
Bars stop about 3 in short of each edge and are tied at every intersection or every other one.
Quick rebar answers
Common slab rebar amounts
10 x 10 slab
16 in grid, #4 bar
9 sticks
112 lb of steel at 20 ft per stick
12 x 12 slab
16 in grid, #4 bar
12 sticks
152 lb of steel at 20 ft per stick
20 x 20 slab
16 in grid, #4 bar
33 sticks
430 lb of steel at 20 ft per stick
Mesh vs rebar
Light residential slabs are sometimes reinforced with welded wire mesh instead of a rebar grid. Follow your plan — this tool estimates a rebar mat only.
Shopping list
Rebar, ties, and supports
Fasten the mat
64 tie points
Tie wire and a twister
Each grid intersection is tied so the mat stays put during the pour. Plan a roll of 16-gauge tie wire and a reel or twister tool.
Cover and support
Chairs and dobie blocks
Rebar sits on chairs or dobies so it lands in the middle of the slab. Space them along each bar per your slab thickness and cover.
Cut and bend
Bolt cutter or rebar cutter
Field cuts and hooks need a rebar cutter/bender or an angle grinder. Add gloves and eye protection for the sharp ends.
Formula shown
How the rebar calculation works
1. Usable span after edge cover
usable = dimension - 2 x edge clearance
2. Bars each direction
bars = floor(usable span / spacing) + 1
3. Total length with overlap
length = (bars x bar length both ways) x (1 + overlap)
4. Sticks and weight
sticks = ceil(length / 20 ft); weight = length x lb per ft
What is not included
This estimate covers a flat slab grid. Footing bars, edge thickenings, vertical dowels, column ties, corner bars, chairs, and welded wire mesh should be counted separately from your plan.
Sources
- HomeGuide rebar prices — 2026 rebar cost per linear foot, per ton, and by project
- The Home Depot rebar — common #3/#4/#5 bar sizes and 20 ft stock lengths
- ASTM A615 rebar unit weights — standard bar weights per foot by size (#3 0.376, #4 0.668, #5 1.043 lb/ft)
Sources checked
Checked against
Bag yields checked against Quikrete and Sakrete product specs; price ranges against published concrete cost guides.
How we check our numbersLast updated: July 3, 2026
Estimate only.
This calculator is not a quote. Verify product yield, price, delivery minimums, and local conditions with your supplier or contractor before buying materials.
FAQ
Rebar calculator questions
Answers for slab rebar spacing, bar size, steel weight, lap overlap, and design limitations.
How do I calculate how much rebar I need for a slab? + -
Set a grid spacing (16 in on center is common for residential slabs), then count bars in each direction as the usable span divided by the spacing, plus one. This calculator does that both ways, adds a lap-splice overlap allowance, and converts the total linear feet into 20 ft sticks.
What size rebar is used in a concrete slab? + -
Residential slabs and driveways commonly use #3 (3/8 in) or #4 (1/2 in) rebar on a 12 to 18 in grid. #4 is the typical default. Footings and structural work often step up to #5 (5/8 in) or larger. Follow your plan or local code.
How much does rebar weigh? + -
Rebar weighs by size: #3 is about 0.376 lb per foot, #4 about 0.668 lb per foot, and #5 about 1.043 lb per foot. The calculator multiplies the total linear feet (with overlap) by the weight for the selected size so you can plan handling and delivery.
How much overlap should I add for rebar splices? + -
Where bars meet end to end they are lapped, not butted. A common rule of thumb is a lap of about 40 bar diameters, and many estimators simply add roughly 10% to the total length to cover splices and cutting. The overlap percentage is editable.
Does this rebar calculator size the reinforcement? + -
No. It estimates quantity for a flat grid only. Bar size, spacing, cover, footing steel, dowels, and whether a slab needs rebar or welded wire mesh are engineering decisions. Verify the design against your plan and local building code.