Rebar Size Chart — Bar Size, Diameter, Area & Weight
Every standard reinforcing bar, #3 through #18, with its nominal diameter, cross-sectional area and weight per foot — plus a take-off that turns a bar list into pounds, kilograms and tons.
Weights are the ASTM A615 nominal unit weights — the mill tolerance allows a small variation, so order by the load table, not by weight. The take-off is computed as quantity × length × the nominal lb/ft from the table on this page, and every figure re-derives the standard formulas area = π/4 × d² and weight = 2.67 × d². Laps and wastage are separate: add the lap length for each splice and a few percent for cut loss before you order.
What a rebar size chart is for
Rebar is sold and specified by a size number, and every other number about the bar — how big it is, how much steel is in it, how much it weighs — is derived from that one figure. That is why the same bar turns up as a "#4" on a drawing, a "½ inch" at the yard, a "No. 13" on a metric spec and an "0.668 lb/ft" on a bill of materials. This page is the translation table between all of those names, plus the two formulas that generate the numbers so you can check any of them by hand.
The chart matters for three practical jobs: converting a drawing that calls out bar numbers into a weight you can price and order, checking that the steel actually delivered matches the spec, and settling the "how much does rebar weigh" arithmetic that decides how many pieces go on a truck.
How the bar number works
A US rebar size is simply the nominal diameter in eighths of an inch. A #4 bar is 4/8 = ½ inch. A #8 is 8/8 = 1 inch. A #5 is ⅝ inch. Once you know the rule the mental conversion is instant, and it is the reason the numbers jump the way they do: #3, #4, #5, #6, #7, #8, #9, #10, #11, then a skip to #14 and #18 for the large bars used in heavy foundations.
The soft-metric designations — No. 10, No. 13, No. 16 and so on — are the same physical bars renamed for a metric market. The soft-metric number is the nominal cross-sectional area in square millimetres, rounded: a #4 bar has a 129 mm² area and is sold as a No. 13. The imperial and soft-metric bars are dimensionally interchangeable in US practice.
The full rebar size chart
Diameters and areas are nominal. The area in the fourth column is the value used in structural design; the last two columns convert the size into the numbers a take-off needs.
| Bar | Soft metric | Diameter | Area | Unit weight | 20 ft stick | Sticks / ton |
|---|---|---|---|---|---|---|
| #3 — ⅜″ | No. 10 | 0.375 in / 9.5 mm | 0.11 in² / 71 mm² | 0.376 lb/ft / 0.56 kg/m | 7.52 lb | 265 |
| #4 — ½″ | No. 13 | 0.5 in / 12.7 mm | 0.2 in² / 129 mm² | 0.668 lb/ft / 0.994 kg/m | 13.36 lb | 149 |
| #5 — ⅝″ | No. 16 | 0.625 in / 15.9 mm | 0.31 in² / 200 mm² | 1.043 lb/ft / 1.552 kg/m | 20.86 lb | 95 |
| #6 — ¾″ | No. 19 | 0.75 in / 19.1 mm | 0.44 in² / 284 mm² | 1.502 lb/ft / 2.235 kg/m | 30.04 lb | 66 |
| #7 — ⅞″ | No. 22 | 0.875 in / 22.2 mm | 0.6 in² / 387 mm² | 2.044 lb/ft / 3.042 kg/m | 40.88 lb | 48 |
| #8 — 1″ | No. 25 | 1 in / 25.4 mm | 0.79 in² / 510 mm² | 2.67 lb/ft / 3.973 kg/m | 53.40 lb | 37 |
| #9 — 1⅛″ | No. 29 | 1.128 in / 28.7 mm | 1 in² / 645 mm² | 3.4 lb/ft / 5.06 kg/m | 68.00 lb | 29 |
| #10 — 1¼″ | No. 32 | 1.27 in / 32.3 mm | 1.27 in² / 819 mm² | 4.303 lb/ft / 6.404 kg/m | 86.06 lb | 23 |
| #11 — 1⅜″ | No. 36 | 1.41 in / 35.8 mm | 1.56 in² / 1006 mm² | 5.313 lb/ft / 7.907 kg/m | 106.26 lb | 18 |
| #14 — 1.693″ | No. 43 | 1.693 in / 43 mm | 2.25 in² / 1452 mm² | 7.65 lb/ft / 11.38 kg/m | 153.00 lb | 13 |
| #18 — 2.257″ | No. 57 | 2.257 in / 57.3 mm | 4 in² / 2581 mm² | 13.6 lb/ft / 20.24 kg/m | 272.00 lb | 7 |
Note that #18 is the largest bar in the standard table carried into residential and light-commercial work; sizes above it are supplied by agreement. The two biggest sizes, #14 and #18, are common in heavy footings and mat foundations and are almost never found in a residential deck or slab.
Area and weight both come from the diameter
Both of the numbers people look up are simple functions of the nominal diameter, and writing them out is the whole point of a chart you can trust:
The 2.67 constant falls out of the unit weight of steel: a one-square- inch bar one foot long holds 12 in³ of steel, and 12 × 0.2836 = 3.40 lb/ft per square inch. Multiply that by the π/4 = 0.7854 shape factor and you get 3.40 × 0.7854 = 2.67. So the weight formula and the area formula are the same formula with the steel density folded in.
Check it against the table. A #6 bar has a diameter of 0.750 in. Area = π/4 × 0.750² = 0.4418 in², which rounds to the published 0.44 in². Weight = 2.67 × 0.750² = 2.67 × 0.5625 = 1.502 lb/ft, which is exactly the table figure. A #8 at 1.000 in gives area π/4 = 0.785 in² (published 0.79) and weight 2.67 lb/ft (published 2.670). The formulas and the table are the same numbers.
Worked example — pricing a footing mat
A 30 ft × 20 ft slab-on-grade is specified with #4 bar at 16 in. on centre both ways, two layers, and 20 ft stock. How much steel is that?
- Bars running the long way. A 30 ft run at 16 in. spacing needs 30 ÷ 1.333 = 22.5, rounded up to 23 bars per layer; each is 20 ft long to span the 20 ft width with hooks. Two layers is 46 bars.
- Bars running the short way. A 20 ft run at 16 in. needs 20 ÷ 1.333 = 15 bars per layer; each is 30 ft long to span the long direction. Two layers is 30 bars.
- Total. 46 + 30 = 76 bars. In 20 ft stock that is 76 × 20 = 1,520 ft of bar.
- Weight. 1,520 ft × 0.668 lb/ft = 1,015 lb. In short tons that is 1,015 ÷ 2,000 = 0.51 ton, or about 461 kg.
- Add laps and waste. Every splice adds a lap — at roughly 25 in. per #4 lap a handful of splices is one or two extra bars — and a cut list rarely comes out perfectly, so a 5% allowance on top (about 8 more bars) is standard. Order the load table, not the raw geometry.
Run those same inputs through the take-off above at #4, 76 bars and 20 ft and you will get 1,520 ft and 1,015.4 lb — the arithmetic is done the same way you just did it, from the nominal lb/ft.
Lap splices — the hidden bar in the order
A lap splice is where two bars overlap so the load passes from one to the other. The overlap is not a fixed distance; it grows with bar diameter, yield strength and concrete strength. For the common case — Grade 60 bar, Class B tension lap in normal foundation concrete — the simplified ACI 318 method gives the lengths below. The IRC refers designers to its own Table R608.5.4(1), so treat this as the estimate you plan with and the code the figure you build to.
| Bar | 3,000 psi | 4,000 psi | 5,000 psi |
|---|---|---|---|
| #3 | 22″ | 19″ | 17″ |
| #4 | 29″ | 25″ | 23″ |
| #5 | 36″ | 31″ | 28″ |
| #6 | 43″ | 37″ | 34″ |
The pattern is the one you would expect: a bigger bar needs a longer lap, and stronger concrete needs a shorter one. A #6 lap of 37 in. at 4,000 psi is a little over 3 ft — on a serial run of bars that adds up faster than people budget for, which is why laps belong in the take-off from the start.
Cover, grade and where rebar is actually required
Two misconceptions follow this chart around. The first is that every footing needs rebar. It does not, prescriptively: IRC R403.1.3 requires minimum footing reinforcement only in Seismic Design Categories D0, D1 and D2. In SDC A, B and C a plain-concrete footing is permitted by the code. That is a floor, not a ceiling — an engineer can still call for bar, and often does.
The second is that the bar can sit anywhere in the concrete. It cannot. Cover protects the steel from corrosion and fire, and IRC R403.1.3.5.3 sets it: 3 inches where concrete is cast against earth, 1½ inches for removable forms exposed to weather with #5 bar and smaller, 2 inches for #6 and larger, and ¾ inch where the concrete is not exposed. Cover is measured to the outside of the bar, so a chair or spacer that is off by half an inch moves the bar out of position.
Grade matters too. The same nominal size comes in Grade 40, 60, 75 and 80, and a higher grade carries more load in the same diameter. ASTM A615 covers carbon-steel bar; ASTM A706 covers the low-alloy, weldable bar used where bars must be welded or where seismic ductility is required. On the bar itself the specification is a printed letter — "S" for A615, "W" for A706 — and the grade is the number or the count of longitudinal grade lines.
Common mistakes with the rebar chart
- Treating nominal weight as exact weight. ASTM A615 allows a mill tolerance on diameter, so a load can weigh a percent or two off the nominal figure. For a small job it is noise; for a truckload it is why you buy on the load list and the mill cert, not on the chart alone.
- Confusing bar size with bar spacing. #4 at 16 in. means a ½ inch bar every 16 inches, not a 4 inch bar. The two numbers travel together on a detail and are read separately.
- Forgetting laps and cut loss. The geometry gives the minimum steel. The order needs laps, hooks, and a waste allowance on top, or the crew runs short at the pour.
- Assuming a bigger number is a bigger area proportionally. Area is π/4 × d², so area grows with the square of the diameter. Going from #4 to #8 doubles the diameter but quadruples the steel — and the weight.
- Mixing imperial and soft-metric on one detail. A #4 and a No. 13 are the same bar, but the metric and inch tables round areas differently. Keep a job in one system end to end.
- Reading the chart as a design. A size chart tells you what a bar is, not how much bar a footing needs. That is an engineering calculation, and this table is only its raw material.
Rebar size FAQ
What size is #4 rebar?
#4 rebar is ½ inch (0.500 in / 12.7 mm) in nominal diameter, with a cross-sectional area of 0.20 in² and a unit weight of 0.668 lb per foot. The number is the diameter in eighths of an inch — a #4 bar is 4/8 = ½ inch — so the same rule gives #3 = ⅜ inch, #5 = ⅝ inch and #8 = 1 inch. There is no such thing as a "half-inch" bar that is different from a #4; they are the same bar.
How much does rebar weigh per foot?
Unit weight in pounds per foot is 2.67 × d², where d is the nominal diameter in inches. For a #4 bar that is 2.67 × 0.25 = 0.668 lb/ft. The table on this page lists the exact nominal weight for every size from #3 (0.376 lb/ft) to #18 (13.600 lb/ft). A 20 ft stick of #4 weighs 13.36 lb.
How many #4 rebar are in a ton?
About 149. A short ton is 2,000 lb, and one 20 ft #4 bar weighs 0.668 × 20 = 13.36 lb, so 2,000 ÷ 13.36 = 149.7 — 149 whole bars. In 30 ft sticks it is 99 bars and in 60 ft sticks 49. The count changes with bar size: a #3 runs about 265 sticks per ton at 20 ft, a #8 about 37.
What does the number on rebar mean?
The size number is the nominal diameter in eighths of an inch: #4 = 4/8 inch. A deformed bar is also rolled with three other marks — a mill or manufacturer mark, the bar size, and a grade marking. The grade appears either as a number (60, 75, 80) or as longitudinal "grade lines": one line is Grade 60, two lines Grade 75, three lines Grade 80 or 100, and no line is Grade 40. A letter at the end identifies the specification — "S" for carbon steel (ASTM A615) or "W" for low-alloy steel (ASTM A706).
What is the difference between #4 and 12 mm rebar?
They are almost the same bar. Soft-metric designations describe the same physical sizes: a #4 (½ in, 12.7 mm) is sold as a No. 13, and a #5 (⅝ in, 15.9 mm) as a No. 16. The soft-metric number is the nominal area in square millimetres rounded — a No. 13 bar has a 129 mm² area. The US #4 and its soft-metric No. 13 equivalent are interchangeable in US design, but the mill tolerances differ slightly, so a metric job stays metric.
How long should a rebar lap splice be?
For Grade 60 bars in a footing or wall, a Class B tension lap is commonly taken from the simplified ACI 318 method: about 25 inches for a #4 and 31 inches for a #5 at 4,000 psi concrete, tightening as the concrete gets stronger. The IRC points to its own Table R608.5.4(1) for the exact figure. This is one area where a rule of thumb is genuinely unsafe — lap length depends on bar size, grade, concrete strength and bar condition, so confirm it against the code your inspector is using.
Does the IRC require rebar in a footing?
Usually not, and that surprises people. IRC R403.1.3 requires minimum reinforcement in concrete footings only in Seismic Design Categories D0, D1 and D2. In Seismic Design Categories A, B and C a plain-concrete footing is permitted. That is the prescriptive minimum, not a recommendation — many footings are reinforced by specification or by an engineer's design regardless of the seismic category, and a foundation supporting concentrated loads, poor soil or expansive clay needs engineering, not the table minimum.
Where these numbers came from
The bar sizes, diameters, areas and unit weights were read on 2026-10-03 from two independent reproductions of the ASTM A615 / A706 table, which agree cell-for-cell on every size from #3 to #18, and every value was re-derived from the standard formulas π/4 × d² and 2.67 × d² as a second check. The Grade 60 lap-splice figures are the simplified ACI 318 Class B method, cross-checked against the 48·db rule and against the set already shipped in this site's rebar calculator (verified 2026-09-01). The cover and seismic-category rules are quoted from IRC R403.1.3 and R403.1.3.5.3. Bar identification markings are per CRSI and ASTM A615.
This is a working reference, not engineering. A size chart tells you what a bar is; it does not tell you how much of it your footing needs. Confirm quantities, laps and cover against your drawings, the code your authority having jurisdiction enforces, and a licensed designer where the loads are anything but ordinary.
Related pages
- Rebar & footing calculator — the IRC footing size table, bar take-off, laps and a bag count
- Concrete calculator — volume, bags and cost for the footing or slab the bar sits in
- Concrete for a slab — the slab thickness, mesh and where reinforcement is actually specified
- Wire ampacity chart — NEC Table 310.16 — the electrical counterpart, a table people get wrong by the column
- Reference tables — every code table, with its source and verification date
- Roof pitch chart — degrees, slope multiplier and rafter length — the other table people look up by number