Rebar Sizes: Diameter, Area and Weight per Foot
Rebar is named by bar number: in CRSI's table a #4 bar has a nominal diameter of 0.5 in[1], an area of 0.2 in²[1] and a weight of 0.668 lb/ft[1], and the table below gives each size from #3 to #8.
Estimates for planning, not professional advice. Read the full notice.
Work it out for your own sizes
Count the rebar for a slabExample to try: Slab length 10 ft, Slab width 10 ft, Bar spacing 1 ft 6 in
Rebar sizes: diameter, area, weight and lap by bar number
Nominal diameter, area, weight per foot and feet of bar in one hundred pounds, for bars number three to number eight
| Bar number | Diameter | Area | Weight per foot | Feet in 100 lb |
|---|---|---|---|---|
| #3 | 0.375 in | 0.11 in² | 0.376 lb/ft | 265.96 ft |
| #4 | 0.5 in | 0.2 in² | 0.668 lb/ft | 149.7 ft |
| #5 | 0.625 in | 0.31 in² | 1.043 lb/ft | 95.88 ft |
| #6 | 0.75 in | 0.44 in² | 1.502 lb/ft | 66.58 ft |
| #7 | 0.875 in | 0.6 in² | 2.044 lb/ft | 48.92 ft |
| #8 | 1 in | 0.79 in² | 2.67 lb/ft | 37.45 ft |
Source: [1]
Diameter, area and weight are from CRSI's table of ASTM standard bars. Feet in one hundred pounds is one hundred divided by the weight per foot.
Reading the table
In this table each bar's nominal diameter in inches is its number divided by eight. The rebar calculator takes the bar number you pick and its weight per foot from these rows, and shows the CRSI lap length for the bar in its assumptions.
Questions
What does #4 rebar mean?
The number is the bar size designation. In CRSI's table of ASTM standard bars each number has a nominal diameter, area and weight per foot, listed above.
How much does rebar weigh per foot?
The weight per foot of each bar size is in the table, taken from CRSI. Multiply it by the length of bar to get the weight.
How many feet of rebar are in a pound?
The table gives feet of bar in one hundred pounds for each size, worked out as one hundred divided by the weight per foot.
How long is the lap for rebar?
The rebar calculator shows CRSI's Class B tension lap for the bar you pick, with the conditions its table states, and lets you type your own lap.
Calculate it for your project
Enter your own sizes to get the amount to buy or the layout figures, with the working shown and a page to print.
Try your own slab in the rebar calculatorSources (1)
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CRSI 2025 Spring Product Catalog (opens in new tab), Concrete Reinforcing Steel Institute, 2025 Spring; values read from the table image on p. 16 of the CRSI catalog (2025 Spring).
Standards or industry body.
“ASTM STANDARD REINFORCING BARS ... Bar Size Designation NOMINAL DIMENSIONS Area (in.2) Weight (lb/ft) Diameter (in.) #3 0.11 0.376 0.375 #4 0.20 0.668 0.500 #5 0.31 1.043 0.625 #6 0.44 1.502 0.750 #7 0.60 2.044 0.875 #8 0.79 2.670 1.000”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 1)
These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.