Rebar Sizes and Grades: Which to Choose

#3 and #4 bars cover most home projects. They are the two sizes you reach for on a patio, a walk, or a standard slab. Each is easy to cut, bend, and tie by hand.

A #3 bar is 3/8 inch across and weighs 0.376 pounds per foot. It is the lightest common size. Use it for light residential work, like a patio, a sidewalk, or a thin slab. It reinforces without adding much weight to the pour. It bends easily for small hooks and corners.

A #4 bar is 1/2 inch across and weighs 0.668 pounds per foot. It is the workhorse of residential concrete. Use it for driveways, most residential slabs, and footings. It carries more load than a #3 and still bends without special tools.

Choose between them by the load and the plan. A foot-traffic patio can use #3 at wider spacing. A driveway that holds a car or truck needs #4. When in doubt on a residential slab, #4 is the safe pick. Follow your local code, which may set a minimum size.

Both sizes ship in 20-foot sticks and tie into a grid the same way. The jump from #3 to #4 adds weight but adds strength. Run both through the rebar calculator to compare the weight before you buy. Match the size to the job, not to what is on the shelf.

#5 and #6 bars handle heavier, structural work. They carry more load than residential sizes. You see them in walls, columns, grade beams, and thick footings. They are harder to bend, so many come pre-bent.

A #5 bar is 5/8 inch across and weighs 1.043 pounds per foot. Use it for structural footings, retaining walls, and slabs that carry real load. It resists bending forces better than a #4. It often needs a bender or a pre-bent order for corners.

A #6 bar is 3/4 inch across and weighs 1.502 pounds per foot. It is the heaviest size in this calculator. Use it for columns, heavy footings, and structural beams. It weighs about four times a #3 bar per foot, so a grid of #6 is heavy. Plan the haul and the lift.

These sizes need longer laps at splices. A lap runs about 40 times the diameter, so a #6 lap is about 30 inches. That adds length to every joint. Larger bars also need more cover and stronger chairs to hold their weight.

Reach for #5 or #6 only when the load calls for it. An engineer or a plan usually specifies these sizes. Do not use them for a simple patio, where a #3 or #4 does the job. Over-sizing wastes steel and weight. Run the size through the calculator to see the weight before you commit.

Grade is the strength of the steel, not its size. It names the yield strength in thousands of pounds per square inch. Grade 40 yields at 40, and Grade 60 yields at 60. A bar of any size can come in either grade.

Grade 40 is the softer, more bendable steel. It bends easily by hand, which helps for hooks and tight corners. It is common in lighter or older residential work. It is harder to find in larger sizes today.

Grade 60 is the stronger, stiffer steel. It is the standard grade for most concrete work now. It carries more load for the same bar size. Most yards stock Grade 60 in the common sizes, so it is what you usually get.

Read the plan for the grade it calls for. Structural work almost always specifies Grade 60. Light residential work may allow Grade 40, but many crews use Grade 60 for everything. The grade does not change the bar size or the spacing you enter in the calculator.

You can tell the grade by the marks rolled into the bar. A Grade 60 bar carries a single line or the number 60 along its length. A Grade 40 bar has no grade line. The size number is also stamped on the bar. Check the marks so you tie the right steel into the grid.

The calculator counts bars and weight by size, not by grade. Grade affects strength, not quantity. So pick the size and spacing from the plan, then confirm the grade at the yard. Both must match what the plan calls for.

Rebar comes with different coatings, and each resists rust to a different degree. The coating protects the steel where moisture reaches it. Pick the coating for the exposure, not just the price.

Black rebar is plain steel with no coating. The name comes from the dark mill scale on the surface. It is the standard bar for most slabs and footings, where the concrete protects it. Light surface rust is fine and even helps the bond. Use black bar for interior slabs and dry sites.

Epoxy-coated rebar has a green epoxy layer bonded to the steel. The epoxy blocks moisture and slows rust. Use it where salt or water reaches the steel, like bridge decks, parking structures, and coastal work. Handle it with care, because a chipped coating creates a weak spot. Tie it with coated wire.

Galvanized rebar has a zinc coating that resists rust. The zinc protects the steel even if the surface is scratched. Use it in wet or marine sites and where epoxy is not specified.

Match the coating to the environment. A dry interior slab needs only black bar. A driveway in a road-salt climate may call for a coating. Coastal and structural work often specifies epoxy or galvanized. The plan or an engineer sets the choice for structural jobs.

The coating does not change the size, spacing, or count in the calculator. It changes how long the steel lasts, not how much you need. So estimate the quantity by size first. Then choose the coating for the site.

The right bar size depends on the job and the load. Here is how the common sizes map to common projects. Always check your local code and plan, which can set a minimum.

For a patio or a light slab, a #3 bar is often enough. The load is foot traffic and furniture. A #3 grid at wider spacing reinforces the slab without much weight. Step up to #4 if the slab will hold more.

For a driveway, a #4 bar is the usual choice. A driveway holds cars and sometimes trucks. A #4 grid at 12 to 18 inches spreads that load. This is the most common residential pick.

For a standard residential slab, a #4 bar covers most cases. Garage floors, shed slabs, and house slabs use it. It balances strength against weight. A #3 may serve a very light slab, but #4 is the safe default.

For footings, the size depends on the load above. A light residential footing may use #4. A footing under a wall or a column often needs #5. Heavy structural footings use #5 or #6. An engineer sizes structural footings.

For walls, columns, and beams, use #5 or #6. These carry structural load and often bending. They usually come from an engineered plan. Do not guess the size on structural work.

Start with the size the plan or code calls for. Then set the spacing and run the rebar calculator. It counts the bars and reports the weight, so you can compare sizes. Match the bar to the job before you order.