Rebar Size Chart: Diameter, Area and Weight (#3 to #18), Plus How to Estimate Rebar

That rule covers most questions. The full chart below adds weight, area and metric equivalents for every standard size, and the second half of this guide shows how estimators turn a rebar schedule into pounds, tons and pieces to order.

Rebar Size Chart (ASTM A615)

Standard US inch-pound bar sizes per ASTM A615 / A706, with the matching soft-metric bar designations. Values as published by the Concrete Reinforcing Steel Institute (CRSI).

Sizes #9 and up no longer match the “eighths of an inch” rule exactly. Their diameters were set so each bar has a round-number area: #9 has 1.00 sq in, and #18 has 4.00 sq in. #12, #15, #16 and #17 are not produced as standard bars.

Most Common Rebar Sizes and Where They Are Used

On residential and light commercial jobs, #4 and #5 bars make up most of the tonnage we take off. Heavier sizes appear mainly in commercial frames, mat foundations and infrastructure.

Rebar Diameters Explained: #3, #4, #5 and #6

These four sizes generate most of the questions, so here they are side by side:

Metric Rebar Sizes

US mills label bars with either inch-pound numbers or “soft metric” numbers. The steel is identical; only the stamp changes. A #13 metric bar is the same as a #4, a #16 is a #5, and a #19 is a #6. The metric number is the diameter rounded to the nearest millimeter. Projects outside the US often use different metric series (10M, 15M, 20M in Canada, or 10, 12, 16 mm bars elsewhere), so always check which system the drawings use.

Rebar Grades and Markings

Size tells you how big a bar is. Grade tells you how strong it is, as its minimum yield strength in thousands of psi:

• Grade 40 (40,000 psi): lighter residential and non-structural work.
• Grade 60 (60,000 psi): the standard for most building construction.
• Grade 80 and higher: heavily loaded columns and high-rise work, where it reduces congestion.

Each bar is rolled with markings in this order: the producing mill, the bar size, the steel type (S for ASTM A615, W for weldable A706) and a grade mark (for Grade 60, either the number 60 or one continuous longitudinal line). Inspectors check these marks against the specs, so the size you order must match what the drawings call for.

Standard Rebar Lengths

Most suppliers stock straight bars in 20 ft, 40 ft and 60 ft lengths. Home centers usually carry 10 ft and 20 ft #3, #4 and #5. Longer bars mean fewer laps but are harder to ship and handle, so commercial projects usually order bars cut and bent to a schedule rather than stock lengths.

How to Estimate Rebar Quantities

Rebar is bought by weight and installed by the piece, so an estimate needs both. This is the sequence our estimators follow:

1. Read the reinforcing schedule and general notes. Note bar sizes, spacing, cover, lap splice lengths and hook requirements for each element.
2. Count bars from spacing. Number of bars = (length to cover / spacing) + 1, for each direction and each layer.
3. Find each bar’s length. Element length minus cover at both ends, plus hooks and bends.
4. Add lap splices. Wherever a run is longer than the stock length, add one lap per splice. Use the splice length on the drawings; a common rule of thumb is 40 to 48 bar diameters, but the engineer’s number governs.
5. Total the linear feet by bar size.
6. Convert to weight. Linear feet x weight per foot from the chart. Divide by 2,000 for tons.
7. Add waste and accessories. Allow about 5% for cut-off and waste on straight stock, and take off chairs, bolsters and tie wire separately.

A quick check for weight per foot: weight (lb/ft) = 2.67 x diameter squared (in). Our guide to concrete reinforcement weight calculation goes deeper on the weight math and lap splices.

Worked Example: Rebar for a 40 ft x 30 ft Slab

A 40 ft x 30 ft slab on grade with #4 bars at 12″ on center each way, using 20 ft stock bars and a 24″ lap (48 bar diameters). Cover is ignored here to keep the math clear.

Two things change this number on a real job: cover, which shortens every bar by a few inches, and edge or thickened-slab bars, which add to it. A slab plan that calls for bars “each way, top and bottom” doubles the whole takeoff.

Fiberglass (GFRP) Rebar vs. Steel Rebar

Glass fiber reinforced polymer (GFRP) rebar is sold in the same nominal sizes as steel and is now covered by its own ACI design code (ACI 440.11). It is worth knowing how it differs before you price it:

GFRP is not a one-for-one swap. Because it is less stiff, an engineer has to design for it, and a #4 GFRP bar is not equivalent to a #4 steel bar. Price it only when the drawings call for it.

Need a Rebar Takeoff or Bar Bending Schedule?

Design Estimation prepares rebar takeoffs and bar lists for general contractors, concrete subcontractors and fabricators across the US, with tonnage by bar size and element, lap and hook allowances, and accessories. Turnaround is typically 24 to 48 hours. See our rebar estimating services, or send your structural drawings for a quote.