Rebar Sizes Chart: Diameter, Weight, and Grade Reference

Use our rebar calculator to turn any bar size and grid spacing into exact bar counts, linear feet, and weight for your slab.

How Rebar Sizing Works: The /8-Inch Rule

US rebar sizes #3 through #8 follow a simple rule: the bar number equals its nominal diameter in eighths of an inch. #3 = 3/8″ (0.375 in). #4 = 4/8″ (0.500 in). #5 = 5/8″ (0.625 in). Keep dividing the size number by 8 and you get the diameter in inches — no chart needed for a quick mental check.

That pattern breaks at #9 and up. Bars #9, #10, and #11 were historically sized to match the cross-sectional area of a 1-inch, 1⅛-inch, and 1¼-inch square bar respectively — a holdover from when rebar was rolled from square stock. #14 and #18 continue the pattern, corresponding to 1½-inch and 2-inch square bar equivalents. That's why #9's actual diameter (1.128 in) doesn't cleanly divide by 8 the way #3-#8 do.

All standard US rebar is manufactured to ASTM A615 (or A706 for low-alloy weldable bar), which fixes the nominal diameter, area, and weight for every size — so a #4 bar from any US mill matches the same spec regardless of supplier. The numbering system itself dates to the early 20th century, when the Concrete Reinforcing Steel Institute (CRSI) standardized bar sizes across US mills; before that, producers rolled their own proprietary shapes and weights, which made specifying and ordering steel across state lines unreliable. The modern chart below is the CRSI/ASTM nominal-weight standard still used by every US supplier today.

If you're working from a metric or international spec sheet, don't assume a "#10" callout means US #10 rebar — some countries number bars directly by their millimeter diameter (a metric #10 is roughly a US #3). Always confirm whether a drawing is using US customary sizes or true metric sizes before ordering.

Master Rebar Size Chart (#3–#18)

Sizes #3 through #8 cover essentially every residential and light-commercial slab, driveway, and footing. #9 through #18 are structural bar sizes — columns, beams, high-rise foundations, and bridge work — and almost never appear in homeowner-scale concrete.

Which Rebar Size for Which Application

Bar size follows load, not thickness. A thin driveway apron carrying vehicle weight needs more steel than a thick decorative slab that only sees foot traffic.

For the load-and-soil logic behind these picks — when a project actually needs steel versus wire mesh — see when to use rebar and rebar vs mesh vs fiber. Once you've settled on a size and spacing, run it through the rebar calculator to get bar counts, linear feet, and cost for your actual slab dimensions.

Structural disclaimer: the sizes and spacings above are general reference points, not an engineered spec. Bar size, spacing, and grade for any load-bearing application should follow stamped engineered drawings or your local building code (IRC/ACI 318) — use this chart to sanity-check a quote or plan a DIY patio, not to substitute for engineering on structural work.

Grade Markings: How to Read a Rebar Stamp

Every US rebar bar is rolled with raised marks running down its length, repeating every couple of feet. Reading them tells you the mill, size, steel type, and grade without cutting or testing the bar:

1. Producer's mark — a letter or symbol identifying the mill that rolled the bar.
2. Bar size number — matches the chart above (3 through 18).
3. Type letter — S for billet steel (ASTM A615, the common type), W for low-alloy weldable steel (ASTM A706), or I for rail-steel bar (ASTM A996, less common today).
4. Grade mark — indicates yield strength:
   • No grade mark = Grade 40 (40,000 PSI yield)
   • One continuous longitudinal line, or the number "60" = Grade 60 (60,000 PSI yield)
   • Two lines, or the number "75" = Grade 75 (75,000 PSI yield)
   • The number "80" = Grade 80 (80,000 PSI yield)

Grade 60 is the default for nearly all US residential and commercial concrete work and is what's assumed in the weight and application tables above. Grade 40 turns up mostly in smaller bars (#3-#6) for light-duty or non-structural work — it's more ductile but weaker. Grade 75 and Grade 80 let structural engineers hit the same strength with less steel volume, common in seismic zones and high-rise construction, but they're rarely specified for anything a homeowner pours.

If a supplier or leftover bar isn't stamped clearly, don't assume — for structural work, ask for a mill certification (mill cert) confirming grade and ASTM designation.

Bar Type and Coatings: A615, A706, and Corrosion Protection

The type letter in a bar's stamp (S, W, or I) tells you which ASTM specification it was rolled to, and that matters beyond just strength:

• ASTM A615 (billet steel, marked "S") — the standard bar for the vast majority of US concrete work, made from recycled steel billets. This is what's assumed everywhere in this guide unless noted otherwise.
• ASTM A706 (low-alloy steel, marked "W") — a "weldable" bar with tighter chemical composition controls, specified where bars will be field-welded or where seismic engineering requires more predictable ductility. Costs more than A615 for the same size.
• ASTM A996 (rail-steel or axle-steel, marked "I" or "A") — reclaimed from old rail stock, less common today, and generally restricted from seismic and critical structural applications.

Corrosion protection adds a size- and grade-independent decision on top of the chart above. Plain black bar (uncoated A615) is standard for interior slabs and typical residential exposure. For coastal construction, projects exposed to deicing salts, or marine/waterfront work, two coating options extend service life:

• Epoxy-coated rebar — a fusion-bonded green or purple epoxy layer that blocks moisture and chloride intrusion. Adds roughly 30-40% to bar cost and requires careful handling — chips and scratches in the coating create localized corrosion points, so epoxy bar needs non-metallic tie wire and padded bar supports.
• Hot-dip galvanized rebar — a zinc coating that sacrifices itself to protect the underlying steel, more durable in handling than epoxy but at a higher cost premium (often 50%+ over black bar).
• Stainless steel rebar — the most corrosion-resistant option and the most expensive by a wide margin, generally reserved for bridge decks, parking structures, and marine infrastructure where a multi-decade service life is required.

For a typical residential driveway or patio in a non-coastal climate, plain black Grade 60 bar is standard and sufficient — coatings add cost that most homeowner-scale projects don't need.

Concrete Cover Requirements by Bar Size

"Cover" is the distance between the outer surface of the rebar and the nearest concrete surface — and per ACI 318, the minimum required cover increases with bar size in some exposure conditions, because larger bars need more surrounding concrete to develop full bond strength and protect against corrosion:

In practice, most residential flatwork uses the "cast against earth" case — a slab poured directly on compacted base or gravel — which calls for a flat 3 inches of cover regardless of bar size, set with rebar chairs or dobies rather than laid on the ground. The size-dependent rows above matter more for formed elements like foundation walls, footings with formed sides, and structural beams.

Weight and Ordering Math

Rebar is sold by the stick (20 ft standard, 10 ft at some home-improvement stores) or by the hundredweight (cwt) for large orders. Three numbers get you from a grid layout to a shopping list:

1. Total linear feet — sum of every bar's length in both directions of your grid, plus a lap-splice allowance (see below).
2. Weight — linear feet × the lb/ft value from the chart above. A 20×20 ft slab gridded with #4 at 16 in o.c. runs roughly 640 linear feet with allowance — about 428 lbs of steel, or 32 twenty-foot sticks.
3. Cost — figure $0.75-1.50 per linear foot at retail for common sizes in 2026; a 20-ft #4 stick runs about $8-13 depending on region and current steel pricing. Buying full sticks from a rebar or masonry supplier beats big-box per-foot pricing at any real quantity.

Lap splices add real footage. Wherever a run is longer than one stick, the joining bars must overlap by 40 bar diameters, tied with wire at both ends:

On a small slab where every bar fits a single 20-ft stick, you can skip splices entirely and trim the allowance. On anything larger, budget roughly 8-10% extra footage for laps and cutting waste — which is exactly what the rebar calculator applies automatically when you enter your slab dimensions and spacing.

Worked example — 24×30 ft slab, #4 bar, 16 in o.c.: the grid needs 41 bars total (18 running one way, 23 the other) for about 1,072 linear feet before allowance. Add the standard 10% for laps and waste and you're ordering roughly 1,179 linear feet — about 59 twenty-foot sticks, weighing close to 788 lbs of steel. At $0.75-1.50 per linear foot, that's $885-1,770 in bar stock alone, before tie wire and chairs. Tightening the same footprint to 12-in spacing pushes the order up by roughly 30%; opening to 24-in spacing cuts it by a similar margin — spacing moves the shopping list far more than switching between adjacent bar sizes does.

Common Rebar Size Mistakes

Undersizing a driveway or garage floor. #3 rebar controls cracking in a patio; it's thinner than most driveways need. #4 is the practical minimum anywhere vehicles will park or drive.

Confusing bar number with actual inches. #10 rebar is 1.270 inches in diameter, not 10 inches or 10/8 — the /8-inch shortcut only applies cleanly through #8. Above that, use the chart.

Ignoring weight when hauling steel yourself. A bundle of #5 rebar for a modest footing project can run 200-400 lbs. Check your vehicle's payload before loading sticks that long and that heavy — most 20-ft bars won't fit in a standard truck bed without hanging past the tailgate.

Skipping the lap-splice allowance when ordering. Buying exactly the calculated grid footage with no allowance leaves you short once splices are tied in on any run longer than 20 ft.

Using an unstamped or unknown-grade bar for structural work. Scrap or unmarked rebar might be Grade 40 dressed up as Grade 60 stock — fine for a decorative garden edge, risky for a footing or foundation wall. Match grade to the engineered spec, not to what's cheapest at the yard.

Mixing up soft-metric and imperial designations on a spec sheet. "13M" and "#4" are the same physical bar — if a plan calls out metric bar numbers and your supplier quotes imperial, convert with the chart above rather than guessing.

Key Takeaways

• Rebar sizes #3-#8 follow the /8-inch rule — the number is the diameter in eighths of an inch (#4 = 4/8″ = ½ inch)
• #3-#4 covers most residential work: patios and light slabs use #3, driveways and garage floors use #4
• #4 rebar weighs 0.668 lb/ft — a 20-ft stick weighs about 13.4 lbs and costs roughly $8-13 at retail
• Grade 60 (60,000 PSI yield) is the US residential/commercial standard; check the stamped mark before assuming grade
• Lap splices need 40 bar diameters of overlap — 20 inches for #4 — tied with wire at both ends
• Bar size and spacing on structural work should always follow engineered drawings or local code, not a general chart

Next Steps

Run your slab or footing dimensions through the rebar calculator to get exact bar counts, linear feet, weight, and cost for the size and spacing you've chosen. For the decision on whether a project needs rebar at all, see when to use rebar; for a full comparison against wire mesh and fiber reinforcement, see rebar vs mesh vs fiber. To size the concrete itself once your steel plan is set, use the concrete slab guide or the concrete footing calculator for continuous footings.