Reinforcing bar in the United States is sold by bar number. The number is the nominal diameter in eighths of an inch, so a #4 bar is 4/8 = 1/2 in and a #5 bar is 5/8 in. That rule holds from #3 to #8; the larger bars (#9, #10, #11, #14 and #18) are sized by their cross-section area instead. This chart gives the diameter, area, weight per foot and per 20 ft stick, and the metric designation of every standard bar, all in the ASTM A615 system. Use our rebar calculator to lay out a slab grid and count the sticks.
Rebar size chart
| Bar size | Metric size | Nominal diameter | Diameter (mm) | Area | Weight | Weight per 20 ft stick | Perimeter |
|---|---|---|---|---|---|---|---|
| #3 | 10 | 0.375 in (3/8) | 9.5 mm | 0.11 in² (71 mm²) | 0.376 lb/ft (0.560 kg/m) | 7.5 lb | 1.178 in |
| #4 | 13 | 0.500 in (1/2) | 12.7 mm | 0.20 in² (129 mm²) | 0.668 lb/ft (0.994 kg/m) | 13.4 lb | 1.571 in |
| #5 | 16 | 0.625 in (5/8) | 15.9 mm | 0.31 in² (200 mm²) | 1.043 lb/ft (1.552 kg/m) | 20.9 lb | 1.963 in |
| #6 | 19 | 0.750 in (3/4) | 19.0 mm | 0.44 in² (284 mm²) | 1.502 lb/ft (2.235 kg/m) | 30.0 lb | 2.356 in |
| #7 | 22 | 0.875 in (7/8) | 22.2 mm | 0.60 in² (387 mm²) | 2.044 lb/ft (3.042 kg/m) | 40.9 lb | 2.749 in |
| #8 | 25 | 1.000 in (1) | 25.4 mm | 0.79 in² (510 mm²) | 2.670 lb/ft (3.973 kg/m) | 53.4 lb | 3.142 in |
| #9 | 29 | 1.128 in | 28.7 mm | 1.00 in² (645 mm²) | 3.400 lb/ft (5.060 kg/m) | 68.0 lb | 3.544 in |
| #10 | 32 | 1.270 in | 32.3 mm | 1.27 in² (819 mm²) | 4.303 lb/ft (6.404 kg/m) | 86.1 lb | 3.990 in |
| #11 | 36 | 1.410 in | 35.8 mm | 1.56 in² (1006 mm²) | 5.313 lb/ft (7.907 kg/m) | 106.3 lb | 4.430 in |
| #14 | 43 | 1.693 in | 43.0 mm | 2.25 in² (1452 mm²) | 7.650 lb/ft (11.384 kg/m) | 153.0 lb | 5.319 in |
| #18 | 57 | 2.257 in | 57.3 mm | 4.00 in² (2581 mm²) | 13.600 lb/ft (20.239 kg/m) | 272.0 lb | 7.091 in |
How to read a bar
Deformed bars are rolled with raised marks that identify them. Reading along the bar you usually find a letter or symbol for the mill that made it, the bar size number (in inch-pound or metric), a letter for the type of steel (S for carbon steel to A615, W for weldable low-alloy steel to A706) and a grade mark. Grade is the minimum yield strength in thousands of psi: Grade 40, 60 and 80 bars have minimum yield strengths of 40,000, 60,000 and 80,000 psi. Grade 60 is the usual grade for houses and slabs. Grade is shown either as a number or by extra longitudinal lines; ask the supplier if the marks are unclear.
Metric and inch bars are the same bars with two names. A #4 bar is a 13 (13 mm, rounded from 12.7 mm); a #5 is a 16. Canadian and European metric bars (10M, 15M, N12 and so on) are a different series with different diameters, so do not substitute them by name.
Weight of a rebar grid
| Bar | 12 in on center each way | 16 in | 18 in | 24 in |
|---|---|---|---|---|
| #3 | 75 lb | 56 lb | 50 lb | 38 lb |
| #4 | 134 lb | 100 lb | 89 lb | 67 lb |
| #5 | 209 lb | 156 lb | 139 lb | 104 lb |
Worked example: slab weight and stick count
A 20 x 24 ft garage slab with #4 bar at 18 in on center both ways, kept 3 in from the edges, needs 17 bars 19 ft 6 in long one way and 14 bars 23 ft 6 in long the other (the count rounds up so the spacing is never wider than 18 in). That is about 660 ft of bar before laps, or 441 lb of steel at 0.668 lb/ft. In #5 bar the same layout would weigh 689 lb. The 23 ft 6 in runs are longer than a 20 ft stick, so each needs a lap splice; the rebar calculator adds the laps and gives the number of sticks to buy.
Choosing a size: what this chart cannot tell you
Bar size, spacing, lap length and concrete cover are structural decisions. For footings, foundation walls, retaining walls, columns and suspended slabs they are set by the building code and by an engineer’s design, and they depend on loads, soil, the concrete strength and the grade of steel. For a simple slab on ground, many builders use #3 or #4 bar at 18 to 24 in each way, mainly to control cracking, but local practice and code requirements vary. Check with your building department, and use a licensed engineer for anything that holds up a structure.
- Concrete cover. Bar must have enough concrete around it to protect it from rust and to bond properly. Concrete cast against soil needs more cover than formed concrete. Support bars on chairs or dobies so they end up in the slab, not on the ground underneath.
- Laps. Where two bars overlap to continue a run, the overlap length is usually specified as a multiple of the bar diameter, so bigger bars need longer laps. Tie laps with wire.
- Bending. Bars can be bent cold to a minimum radius that grows with bar size; tight bends crack the steel. Corner bars and stirrups are usually ordered pre-bent.
Frequently asked questions
What size is #4 rebar?
1/2 in (12.7 mm) nominal diameter, metric size 13. It weighs 0.668 lb per foot, or 13.4 lb for a 20 ft stick.
How much does #5 rebar weigh?
1.043 lb per foot (1.552 kg/m), about 20.9 lb per 20 ft stick. Its diameter is 5/8 in.
What do rebar numbers mean?
From #3 to #8 the number is the diameter in eighths of an inch: #3 is 3/8 in, #6 is 3/4 in, #8 is 1 in. Larger bars keep the number series but are sized by area: a #9 bar has an area of 1.00 in².
What is the metric equivalent of #3 rebar?
Size 10 in ASTM A615M (9.5 mm nominal). Note that Canadian 10M bar is a different size (11.3 mm).
Why is rebar marked with letters and numbers?
The rolled marks identify the mill, bar size, type of steel and grade, so inspectors can check that the right bar was used.
Sources and method
- ASTM A615/A615M, Standard Specification for Deformed and Plain Carbon-Steel Bars for Concrete Reinforcement: bar designations, nominal diameters, areas and weights, grade marks (values as published in mill certificates and supplier tables; the standard itself is not reproduced here).
- ASTM A706/A706M, Low-Alloy Steel Deformed and Plain Bars for Concrete Reinforcement (weldable bars, marked W).
- Our computation: area = π/4 × d², weight = area × 490 lb/ft³ (density of carbon steel) ÷ 144, metric = inch × 25.4, grid weight as shown in its caption.
Last reviewed: 24 October 2026. How we build and check our data: methodology and corrections. Related: rebar calculator, concrete slab calculator, footing calculator, all calculators. Spotted an error? Please let us know.