Rebar Size Chart: US Bar Sizes, Diameter and Weight

What #4 rebar means, the diameter, area and weight of every standard US bar size, their metric and Canadian equivalents, which sizes go in slabs, footings and walls, and how to identify a bar on site.

Updated

Cross-sections of rebar sizes #3 to #8 drawn to scale with their ribbed outlines, each labeled with its bar number and diameter in eighths of an inch and millimeters

US rebar sizes are numbers: #3, #4, #5 and so on. Up to #8, the number is the diameter in eighths of an inch: #4 is 4/8 = 1/2 inch, #6 is 6/8 = 3/4 inch. Bars are marked on site by their raised ribs and rolled-in letters, not by color.

Rebar size chart

Bar size Diameter (in) Diameter (mm) Area (sq in) Weight (lb/ft) Metric bar
#3 0.375 (3/8) 9.5 0.11 0.376 #10
#4 0.500 (1/2) 12.7 0.20 0.668 #13
#5 0.625 (5/8) 15.9 0.31 1.043 #16
#6 0.750 (3/4) 19.1 0.44 1.502 #19
#7 0.875 (7/8) 22.2 0.60 2.044 #22
#8 1.000 25.4 0.79 2.670 #25
#9 1.128 28.7 1.00 3.400 #29
#10 1.270 32.3 1.27 4.303 #32
#11 1.410 35.8 1.56 5.313 #36
#14 1.693 43.0 2.25 7.650 #43
#18 2.257 57.3 4.00 13.600 #57

Sizes and weights are the nominal values in ASTM A615, the standard for US deformed rebar. The metric bar is the same physical bar with a soft-metric label (#4 is sold as #13 in metric projects); the number is roughly the diameter in millimeters. The diameter is nominal: with the ribs, a bar measures a little more across.

Weight of common lengths

Bar 10 ft 20 ft
#3 3.8 lb 7.5 lb
#4 6.7 lb 13.4 lb
#5 10.4 lb 20.9 lb
#6 15.0 lb 30.0 lb

Multiply the weight per foot by the total length for anything else.

Typical uses

Bar Common residential and light-commercial uses
#3 Patios, sidewalks, light slabs, ties and stirrups
#4 Driveways, garage slabs, footings, block walls
#5 Foundation walls, footings, retaining walls
#6 to #8 Beams, columns, heavier foundations
#9 and up Commercial structures, bridges, heavy columns

These are typical choices, not a design. Bar size, spacing and cover (the concrete between the bar and the surface, usually 1.5 to 3 inches) for anything structural come from the local building code or an engineer. To work out how much concrete and how many bags a slab or footing needs, use the concrete calculator for slabs and footings.

Canadian rebar sizes

Canada uses its own metric sizes, named by approximate diameter in mm:

Bar Diameter Close US size
10M 11.3 mm between #3 and #4
15M 16.0 mm #5
20M 19.5 mm #6
25M 25.2 mm #8
30M 29.9 mm #9
35M 35.7 mm #11

How to identify a rebar size

  1. Read the marks. US bars are rolled with a sequence of letters and numbers along one side: the mill’s mark, the bar size number, the steel type (S for A615 carbon steel, W for weldable A706) and often the grade (60 or a single line for grade 60).
  2. Measure across the bar between the ribs with calipers, or hold it against a ruler: about 1/2 inch is a #4, about 5/8 is a #5. Measuring over the ribs reads about 1/16 inch more.
  3. Weigh a known length if you have a scale: a 20 ft bar that weighs about 13 lb is a #4.

For other sizes on the job, see the pipe size chart and lumber sizes. To convert diameters, use inches to mm.

More DIY charts: sheet metal gauge · plywood and drywall thickness · nail sizes · wrench sizes.

Frequently asked questions

What size is #4 rebar?

#4 rebar is 1/2 inch (12.7 mm) in diameter and weighs 0.668 pounds per foot. US bar numbers count eighths of an inch, so #4 = 4/8 = 1/2 inch, #5 = 5/8 inch and #6 = 3/4 inch.

What rebar size for a concrete driveway or patio?

#3 (3/8 in) or #4 (1/2 in) bars on a grid about 18 to 24 inches apart are common for residential slabs, held up on chairs so they sit in the middle of the slab. Many driveways use welded wire mesh or fiber instead; local code and soil conditions decide.

How much does a 20 foot piece of #5 rebar weigh?

About 20.9 pounds: #5 rebar weighs 1.043 pounds per foot, and 20 × 1.043 = 20.86 lb. Rebar is commonly sold in 20 ft lengths, and 10 ft lengths at home centers.

What is the metric equivalent of #5 rebar?

#5 rebar is the same bar as metric #16 (16 mm nominal diameter) in the US soft-metric system. In Canada the nearest size is 15M, which is 16.0 mm.

Why are #9, #10 and #11 not exact eighths of an inch?

From #9 up, the bar number no longer equals the diameter in eighths. These sizes were originally based on square bars (1 in, 1 1/8 in and 1 1/4 in square), and the round bars that replaced them kept the same cross-section area, so #9 is 1.128 in across rather than 1.125.

More measuring guides