Rebar sizes and weight chart: every bar from #3 to #18, with a takeoff calculator

Rebar size chart: diameter, area and weight

These are the standard inch-pound bar sizes in ASTM A615 and A706, with the soft metric size stamped on bars made to the metric version of the same standard. The steel is identical; only the label differs.

Watch the overlap in names. A metric #10 bar is a 3/8 inch bar, the same as an inch-pound #3, while an inch-pound #10 is a 1-1/4 inch bar more than eleven times heavier. When a schedule mixes the two, or a supplier quotes in metric, confirm which system each size is in before converting to pounds.

Weight per bar, and how many feet are in a ton

Bars are commonly stocked in 20, 40 and 60 foot lengths, and rebar is bought and priced by weight. This table converts both ways.

What the size numbers mean

For #3 through #8, the bar number is the nominal diameter in eighths of an inch: a #3 is 3/8 inch, a #6 is 3/4 inch and a #8 is 1 inch. Above #8 that rule stops working. Sizes #9, #10 and #11 were set to match the cross-sectional area of the old 1, 1-1/8 and 1-1/4 inch square bars, which is why a #9 bar has an area of exactly 1.00 square inch and a diameter of 1.128 inches rather than 9/8. The same applies to #14 and #18, which match 1-1/2 and 2 inch square bars.

The metric names are the nominal diameter rounded to the nearest millimeter: #13 is 12.7 mm, #16 is 15.9 mm. That is why a metric bar number is always larger than the inch-pound number for the same bar.

There is no #12, #13 or #15 to #17 in the inch-pound series, and #14 and #18 are produced mainly for heavy columns, mat foundations, bridges and other civil work. On most buildings, the schedules use #3 to #11.

How to calculate rebar weight

Steel weighs about 490 pounds per cubic foot. A bar one foot long with an area of A square inches holds A ÷ 144 cubic feet of steel, so its weight is 490 × A ÷ 144, or 3.4 × A pounds. Written with the diameter, d, in inches, that becomes the formula estimators remember:

• Weight per foot (lb/ft) = 2.67 × d². For a #5 bar: 2.67 × 0.625² = 1.043 lb per foot.
• Weight per meter (kg/m) = d² ÷ 162, with d in millimeters. For a #16 bar: 15.9² ÷ 162 = 1.56 kg per meter.
• Total weight (lb) = total length (ft) × weight per foot. 1,200 feet of #4 is 1,200 × 0.668 = 802 lb.
• Tons = pounds ÷ 2,000. Fabricators and suppliers usually quote by the hundredweight (100 lb) or the ton.

For a slab or mat with bars both ways, the weight per square foot is 2 × (12 ÷ spacing in inches) × weight per foot. It is the quickest check on a slab takeoff:

Rebar grades and how to read the markings

The grade is the minimum yield strength in thousands of pounds per square inch. Grade 60, 60,000 psi, is the standard bar for building work. Grade 40 is still made in the smaller sizes, and Grades 75, 80, 100 and 120 are used where the engineer wants less steel or less congestion, mostly in columns, shear walls and heavily loaded foundations.

Every deformed bar is rolled with four marks, read from one end. The Concrete Reinforcing Steel Institute describes them in order:

• The mill that made the bar, as a letter or symbol.
• The size, inch-pound or metric.
• The type of steel: S for carbon steel to ASTM A615, W for low-alloy steel to ASTM A706, which is the bar specified when rebar has to be welded or when seismic detailing calls for it.
• The grade, as a number or as lines: one line for Grade 60, two for 75, three for 80 and 100, four for 120. Grade 40 bars carry no grade mark.

In an estimate, grade, type and coating each change the price, so they are separate lines. Epoxy-coated and galvanized bars cost more per pound than black bar, and they are fabricated and handled with more care.

How a rebar takeoff is done

A rebar takeoff counts every bar on the structural drawings, element by element, and converts the length of each size to pounds. Done properly, it follows the order a detailer would:

• Read the general structural notes first. They set the grade, the concrete cover, the lap lengths and the standard hooks. A takeoff measured before the notes are read uses the wrong lengths everywhere.
• Work from the schedules. Footing, pier, column, beam, wall and slab schedules list the bar size, count and spacing for each mark. Typical details cover the rest: corner bars, bars around openings, dowels into walls and columns.
• Measure bar lengths net of cover. Under ACI 318, concrete cast against and permanently in contact with the ground needs 3 inches of cover; formed concrete exposed to earth or weather needs 2 inches for #6 bars and larger and 1-1/2 inches for #5 and smaller; interior slabs and walls need 3/4 inch for #11 and smaller.
• Add laps and hooks. A lap splice is taken from the lap schedule, which ACI 318 bases on bar size, grade, concrete strength and position. For Grade 60 bar in 4,000 psi concrete it typically works out to roughly 40 to 80 bar diameters, about 20 to 40 inches on a #4. A standard 90 degree hook adds a straight extension of 12 bar diameters beyond the bend.
• Total by size and by element, then convert to pounds. Keeping footings, walls, columns and slabs apart lets the price follow the labor, because placing column ties costs far more per pound than placing a slab mat.
• List the accessories separately: chairs and bolsters by count or linear foot, tie wire, mechanical couplers and dowel bar supports.

The method is the same one that runs through every trade; the general approach and its units are in what is a quantity takeoff.

Rebar weight calculator for slabs and mats

Enter a slab or mat reinforced both ways. The calculator counts the bars in each direction, adds the lap splices that the stock length forces, and returns the linear feet, the weight and the number of stock bars to order. It is meant for checking one element; a building needs every schedule and detail taken off.

Two takeoffs, worked through

A slab, by hand. A 60 by 40 foot slab on grade with #4 bars at 12 inches each way, bars stopping 3 inches short of each edge, in 20 foot stock with a 48 bar diameter lap (24 inches):

A real job. On a public trail project in Douglas County, Colorado, we took off 26,847 square feet of 6-inch concrete sidewalk with #4 bars at 16 inches each way. The straight bar alone is 26,847 × 1.002 = 26,901 lb. The delivered takeoff carried 32,313 lb, about 20 percent more, for laps, edge bars and waste. The rest of that takeoff, from the area to the 497 cubic yards of concrete, is in what is a quantity takeoff.

Pounds of rebar per cubic yard: why the ratio misleads

A common shortcut prices rebar as pounds per cubic yard of concrete. The two jobs above show why it fails. The sidewalk carried 32,313 lb in 497 cubic yards, about 65 lb per cubic yard. The slab, at 6 inches thick, holds 44.4 cubic yards and 3,494 lb, about 79 lb per cubic yard, with the same bar size. Columns, transfer beams and shear walls on the same building can carry several times either figure.

A ratio is useful only to check a finished takeoff against similar work. Priced on its own, it carries somebody else's building into your bid. That is why our concrete and rebar estimates take rebar off bar by bar from the schedules.

Common rebar takeoff mistakes

• Measuring bars to the face of the concrete instead of net of cover, which overstates every length.
• Leaving out lap splices, or using one lap length for every bar size.
• Missing dowels, corner bars and the extra bars around openings that only the typical details show.
• Counting a typical floor once instead of once per floor, or a typical footing once instead of once per mark.
• Pricing all rebar at one rate per pound, when ties, stirrups and small bent bars cost far more to fabricate and place than straight slab bar.
• Confusing metric and inch-pound sizes, so a #10 is priced at the wrong weight.
• Forgetting chairs, bolsters, tie wire and couplers, or the coating on epoxy or galvanized bars.

Getting a rebar takeoff done for you

We take off rebar for concrete contractors, rebar fabricators and general contractors in every state, bar by bar from the schedules and details, with the weight by size and by element and marked-up drawings showing where every bar was counted. Most jobs are delivered in 24 to 48 hours. See concrete and rebar estimating, or send the drawings for a free quote.

Common questions

Sources

• ASTM A615/A615M: Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement
• ASTM A706/A706M: Deformed and Plain Low-Alloy Steel Bars for Concrete Reinforcement
• Concrete Reinforcing Steel Institute (CRSI), Bar Identification
• Concrete Reinforcing Steel Institute (CRSI), Rebar Properties
• American Concrete Institute, ACI 318-19: Building Code Requirements for Structural Concrete