What does the rebar number mean?

The bar number is the nominal diameter in eighths of an inch. #4 bar is 4/8 = 0.500 inches, #5 is 5/8 = 0.625 inches, and #8 is 8/8 = 1.000 inch.

How much does #4 rebar weigh per foot?

0.668 lb per foot. A 20 ft stick weighs about 13.4 lb. #3 is 0.376 lb/ft, #5 is 1.043 lb/ft and #6 is 1.502 lb/ft.

What is the metric equivalent of #4 rebar?

No. 13, a soft metric designation naming the diameter in millimetres: #3 is No. 10, #4 is No. 13, #5 is No. 16 and #6 is No. 19.

What is the cross-sectional area of #5 rebar?

0.307 square inches, from pi x d² / 4 with d = 0.625 inches. Area matters because tensile capacity scales with it.

Rebar Size Chart

Diameter, cross-sectional area, weight per foot, stick weights and metric designation for US deformed bar #3 through #11.

Quick answer

A rebar number is its diameter in eighths of an inch — #4 bar is 4/8 = 0.500 in and weighs 0.668 lb per foot. Residential slabs use #3 or #4; footings and foundation walls use #4 or #5.

US rebar sizes

Bar	Metric	Diameter (in)	Diameter (mm)	Area (in²)	Weight (lb/ft)	20 ft stick	Typical use
#3	No. 10	0.375	9.5	0.11	0.376	7.5 lb	Slabs on grade, sidewalks, small footings
#4	No. 13	0.5	12.7	0.196	0.668	13.4 lb	Driveways, patios, residential footings
#5	No. 16	0.625	15.9	0.307	1.044	20.9 lb	Foundation walls, heavier slabs, piers
#6	No. 19	0.75	19	0.442	1.503	30.1 lb	Structural footings, grade beams
#7	No. 22	0.875	22.2	0.601	2.046	40.9 lb	Columns and beams
#8	No. 25	1	25.4	0.785	2.673	53.5 lb	Columns, heavy beams
#9	No. 29	1.125	28.6	0.994	3.383	67.7 lb	Heavy structural work
#10	No. 32	1.25	31.8	1.227	4.176	83.5 lb	Heavy structural work
#11	No. 36	1.375	34.9	1.485	5.053	101.1 lb	Heavy structural work

Diameter is bar number / 8 inches; area is pi x d²/4; weight is area x 12 in x 0.2836 lb/in³.

Published figure

Lap splice lengths at 40 bar diameters

Bar	30d	40d	50d
#3	11.3 in	15 in	18.8 in
#4	15 in	20 in	25 in
#5	18.8 in	25 in	31.3 in
#6	22.5 in	30 in	37.5 in
#7	26.3 in	35 in	43.8 in

A residential rule of thumb only. Structural splices follow code development lengths.

Reading the chart

Two properties do the work. Diameter tells you whether the bar will fit your cover and bend radius; area tells you how much tension it can carry, and since area goes with the square of the diameter, #5 bar carries about 56 percent more than #4 rather than 25 percent more.

Weight matters for ordering and for what you can carry. A 20 ft stick of #4 is a one-person lift at 13 lb; a 20 ft stick of #8 is 53 lb and awkward. Big-box stores usually stock 10 and 20 ft lengths of #3 through #5.

Grade is separate from size. Grade 40 and Grade 60 bar of the same number are physically identical — the grade is the yield strength in ksi. Grade 60 is the common default.

Source & method: All figures are derived, not transcribed: diameter comes from the bar designation, area from pi x d²/4, and weight per foot from area x 12 in x the density of steel (0.2836 lb/in³). This reproduces the published nominal weights to three decimals without copying a specification table.

Rebar and accessories

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Frequently asked questions

What does the rebar number mean?: The bar number is the nominal diameter in eighths of an inch. #4 bar is 4/8 = 0.500 inches, #5 is 5/8 = 0.625 inches, and #8 is 8/8 = 1.000 inch.
How much does #4 rebar weigh per foot?: 0.668 lb per foot. A 20 ft stick weighs about 13.4 lb. #3 is 0.376 lb/ft, #5 is 1.043 lb/ft and #6 is 1.502 lb/ft.
What is the metric equivalent of #4 rebar?: No. 13, a soft metric designation naming the diameter in millimetres: #3 is No. 10, #4 is No. 13, #5 is No. 16 and #6 is No. 19.
What is the cross-sectional area of #5 rebar?: 0.307 square inches, from pi x d² / 4 with d = 0.625 inches. Area matters because tensile capacity scales with it.