What Size Rebar for a Driveway? (2026 Guide)

Most residential concrete driveways use #3 rebar, which is 3/8 inch in diameter, spaced 12 to 18 inches apart in a two way grid. A 5 to 6 inch driveway slab, or one that carries trucks and RVs, steps up to #4 rebar at 1/2 inch. Below is how to pick the right bar size, spacing, and how to get an exact count for your slab.

#3 vs #4 rebar for a driveway

For a standard 4 inch residential driveway, #3 rebar is the default choice. It is 3/8 inch in diameter, easy to bend and tie, and strong enough for typical car and light truck loads over a properly prepared base.

#4 rebar, at 1/2 inch, steps up the capacity by roughly 78% in yield strength over #3, according to ASTM A615 bar data. Use #4 when the slab is poured at 5 or 6 inches, when the driveway sees delivery trucks, RVs or heavy equipment, or where expansive clay or freeze thaw cycles move the subgrade every year.

A practical rule ties bar size to slab depth: the bar diameter should not exceed about 1/8 of the slab thickness. That puts a 4 inch slab at #4 or smaller, and a 6 inch slab comfortably within #4 or even #5 territory for the busiest driveways.

Run the numbers for your own slab in the rebar calculator to get the total footage and piece count before you order steel.

Rebar spacing and grid pattern for a driveway

Rebar in a driveway is laid as a two way grid, bars running one direction and overlapping with bars running perpendicular, tied at each intersection. Spacing is measured on center, meaning from the middle of one bar to the middle of the next.

Driveway type	Slab thickness	Bar size	Spacing (on center)
Light duty (cars only)	4 in	#3	18 to 24 in
Standard residential	4 in	#3	12 to 16 in
Heavy duty / freeze-thaw	5 to 6 in	#4	12 in
Apron / street transition	6 in	#4	12 in

The building code most contractors reference, ACI 318, caps shrinkage and temperature reinforcement spacing at 5 times the slab thickness or 18 inches, whichever is smaller. For a 4 inch slab, that math tops out at 18 inches, which is why 12 to 18 inch grids are the common range in practice.

The apron, where the driveway meets the street, takes the most stress from turning wheels and weight transfer. Many contractors thicken this section to 6 inches and tighten the grid to 12 inches on center even if the rest of the driveway uses a wider spacing.

How to calculate the rebar you need

Once you know the bar size and spacing, the layout is straightforward: divide the slab width by the spacing to get the number of bars running one way, then do the same for the length to get the bars running the other way. Add up the total linear feet, then add 10% for laps and waste.

For a 20 by 20 foot driveway with #3 rebar on a 12 inch grid, that works out to roughly 400 linear feet of bar before waste, or about 2 linear feet of rebar per square foot of slab, a ratio that holds for most 12 inch grids regardless of bar size.

For the full breakdown by slab size, see how much rebar do I need, or enter your driveway's length, width and grid spacing directly into the rebar calculator to get the piece count and total cost.

Close-up of rebar chairs holding a steel grid off the ground in a driveway form

Rebar size chart and cost by bar number

Rebar sizes are numbered by eighths of an inch in diameter under ASTM A615, the US standard for deformed steel bar. A #3 bar is 3/8 inch (3 x 1/8), a #4 bar is 1/2 inch (4 x 1/8), and a #5 bar is 5/8 inch, used mainly in footings and foundations rather than driveway slabs.

For the complete reference across all common bar numbers and their metric equivalents, see the rebar size chart. Grade 60 rebar, the standard grade for residential work, has a minimum yield strength of 60,000 PSI regardless of diameter.

Steel prices swing with the commodity market, so budget in a range rather than a fixed number. For current per-foot and per-ton pricing, see how much does rebar cost.

Rebar placement and cover in a driveway slab

Rebar needs to sit inside the concrete, not on the ground or at the surface. Use plastic or metal rebar chairs to hold the grid at mid depth to mid-to-upper third of the slab, typically 1.5 to 2 inches of concrete cover above the steel for a residential driveway.

Keep the grid at least 2 to 3 inches back from the slab edges on all sides. Bars placed too close to an edge or too shallow are prone to corrosion and can eventually cause the surface to spall or crack along the bar line.

Some driveway contractors use welded wire mesh instead of rebar for 4 inch slabs with light loads. Mesh is faster to install but harder to keep at the correct height during the pour, and most engineers rate a properly placed rebar grid as more reliable for driveways over the long term.

How we check this

Every formula is shown in full and verified with automated tests against manufacturer spec sheets and ASTM and ACI standards. We show our work so you can check it.

Frequently asked questions

Is 3/8 rebar good for a driveway?

Yes, 3/8 inch rebar, known as #3 rebar, is the standard choice for a typical 4 inch residential driveway carrying cars and light trucks, placed on a 12 to 18 inch grid.

Is 4 inches of concrete thick enough for a driveway?

4 inches is thick enough for a standard residential driveway with normal passenger vehicle traffic, but 5 to 6 inches is recommended if the driveway will regularly carry trucks, RVs, or heavy equipment.

How far apart should rebar be for a driveway?

Rebar in a driveway is typically spaced 12 to 18 inches apart on center in a two way grid, with 12 inches used for heavier loads or freeze thaw climates and up to 18 to 24 inches for light duty slabs.

Should you put rebar in a concrete driveway?

Yes, rebar is recommended for driveways because it holds cracked sections together and resists the load, soil movement, and freeze thaw stress that a driveway slab is exposed to over its lifespan.

What Size Rebar for a Driveway?

Key takeaways