ASTM A615 · Rebar sizes explained

How rebar sizes work

What the bar number means, how to read the marks on the bar, what Grade 40/60/80 means, and how to work out area and weight per foot yourself — with worked examples.

Where the official numbers live

Nominal bar dimensions and grades are set by ASTM A615/A615M (carbon-steel bar) and ASTM A706/A706M (low-alloy, weldable bar), published by ASTM International. For day-to-day work, your rebar fabricator's submittal, the mill test report, and the Concrete Reinforcing Steel Institute (CRSI) manuals list every size. The structural drawings govern bar size, grade, spacing, and cover.

Standards are revised periodically and your project spec names the edition that applies. Not engineering advice.

Reading the marks rolled onto a bar

Mark	What it tells you
Bar size mark	The number rolled onto the bar. On soft-metric bar it is the approximate diameter in mm (a #4 is marked 13); on inch-pound bar it is the U.S. bar number.
Producing mill	A letter or symbol identifying the mill that rolled the bar — this ties the bar back to its mill test report.
Type of steel	Usually "S" for carbon steel (A615) or "W" for low-alloy weldable steel (A706). Other letters cover rail and axle steel.
Grade	Shown by a number (for example 60) or by extra longitudinal grade lines. Grade = minimum yield strength in ksi.

What the grade means

Grade / type	What to know
Grade 40	40,000 psi minimum yield. Lower strength, more ductile; seen in some residential and older work, and in smaller bar sizes.
Grade 60	60,000 psi minimum yield. The default for most U.S. commercial, industrial, and residential structural concrete.
Grade 80	80,000 psi minimum yield. Used where the engineer wants less steel congestion (columns, walls, heavy foundations). Recent editions of the standards also cover higher grades.
A706 vs. A615	A706 bar has controlled chemistry for welding and tighter ductility requirements — often specified for seismic frames or when bars will be welded. Do not substitute A615 for A706 without the engineer's approval.

Worked examples — area and weight from the diameter

Example	Input	Steps	Result
A. #4 bar	Diameter 0.500 in (4/8").	Area = π × 0.500² ÷ 4 = 0.1963 in². Weight = 0.1963 × 3.403 = 0.668 lb/ft.	≈ 0.20 in² and 0.668 lb/ft
B. #5 bar	Diameter 0.625 in (5/8").	Area = π × 0.625² ÷ 4 = 0.3068 in². Weight = 0.3068 × 3.403 = 1.044 lb/ft.	≈ 0.31 in² and 1.04 lb/ft
C. Takeoff	1,200 LF of #5 bar.	1,200 × 1.044 lb/ft = 1,253 lb. Divide by 2,000 for tons.	≈ 0.63 tons (add laps and waste)

3.403 lb/ft per in² comes from steel's density (490 lb/ft³ ÷ 144 in²/ft²). Published nominal weights may differ in the last digit from rounding. Confirm diameters for other sizes with your supplier or the standard.

Common field mistakes

Mistake	What to do instead
Assuming the eighths rule for big bars	It is a rule of thumb for #3–#8 only. Get larger-bar diameters from the supplier or standard.
Forgetting lap and hook length in takeoffs	Linear feet from the plan view is not what you order. Add lap splices, hooks, and development length — see the lap splice guide.
Mixing up soft-metric marks	A bar stamped 16 is a #5, not a 16 mm "M" bar from a Canadian series. Check the mark against the submittal.
Substituting grade	A lower grade or a non-weldable bar is not an equal substitution. It needs an approved RFI or submittal.
Skipping the mill cert	Keep mill test reports with the delivery ticket. Inspectors and owners on commercial work routinely ask for them.

Need the pour quantity too? Try the free concrete calculator.

📋 Embed this chart on your site — freeGet the code →

Paste this where you want the live chart to appear. It works on any site that allows iframes, and includes a link back to Field PM.

<iframe src="https://www.field-pm.com/embed/charts/rebar-size-chart" title="Rebar Sizes & Weights Explained — Field PM" width="100%" height="640" loading="lazy" style="border:1px solid #e5e7eb;border-radius:12px;max-width:560px;width:100%"></iframe>
<p style="font:13px/1.5 system-ui,sans-serif;margin:8px 0;color:#6b7280"><a href="https://www.field-pm.com/charts/rebar-size-chart" target="_blank" rel="noopener">Rebar Sizes & Weights Explained</a> by <a href="https://www.field-pm.com" target="_blank" rel="noopener">Field PM</a></p>

Reading rebar sizes in the field

U.S. reinforcing bar is identified by a bar number. For #3 through #8 the number is a handy rule of thumb for the nominal diameter in eighths of an inch — a #5 is about 5/8". Soft-metric bar carries the same steel with a millimeter mark instead (a #4 is marked 13).

You rarely need a table to get the two numbers that matter for takeoff and checking drawings. Area = π × d² ÷ 4, and because steel weighs about 490 lb/ft³ (490 ÷ 144 ≈ 3.40 lb per ft for every in² of steel), weight per foot is just area × 3.40.

Lap lengths come from the structural drawings — see how rebar lap splices are calculated. The concrete calculator handles pour yardage, and Field PM keeps rebar inspections, pour cards, and mill certs in the QA/QC job book.

FAQ

What does the rebar number mean?+

For the common small bars (#3 through #8), the bar number is a good rule of thumb for the nominal diameter in eighths of an inch — a #4 is about 4/8" (1/2") and a #5 about 5/8". Above #8 the numbering continues, but the eighths rule no longer holds, so read the diameter from the mill certificate, the bar supplier, or the ASTM standard.

What is the diameter and weight of #4 rebar?+

A #4 bar is nominally 1/2" (0.500") in diameter. Its area is π × 0.5² ÷ 4 ≈ 0.196 in², usually rounded to 0.20 in², and its nominal weight works out to about 0.668 lb per foot.

How do I calculate rebar weight per foot?+

Steel weighs about 490 lb per cubic foot, which is about 3.40 lb for every square inch of cross-section per linear foot. Multiply the bar's nominal area (in²) by 3.40 to get lb/ft, then multiply by the total linear feet for your takeoff.

What does Grade 60 rebar mean?+

The grade is the minimum specified yield strength in thousands of psi (ksi). Grade 60 bar has a minimum yield of 60,000 psi and is the most common grade in U.S. building work. Grade 40 is lower-strength and Grade 80 higher; the structural drawings specify which one to use.

What are soft-metric rebar sizes?+

Soft-metric bars are the same physical bar labeled by approximate diameter in millimeters: a #4 bar is marked #13 and a #5 bar #16. The steel is identical — only the mark rolled onto the bar differs. Hard-metric (Canadian "M") bars are a different series.

Built by a contractor, for the field

Field PM runs daily reports, job costing, QA/QC, and billing in one platform — $99/month with unlimited foremen, QA/QC, and safety free. 30-day trial, no credit card.

Start free trial →

The Field PM platform

Construction project management software →Electrical contractor software →Software for subcontractors →Daily field reporting app →GPS construction time clock →AIA G702 / G703 billing software →Weld mapping & tracking software →

More reference charts

Rated by contractors on