Concrete (C-8) · Lesson 1 of 7

Reading a Rebar Callout

"Reading a Rebar Callout" is lesson 1 of 7 in the Concrete (C-8) Learning Hub. It opens with "A Callout Packs Three Facts Into One Line" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. A Callout Packs Three Facts Into One Line
  2. Decode the Bar Number - Nominal Diameter in Eighths of an Inch
  3. Decode the Spacing - O.C. Means Center to Center
  4. Decode the Direction - E.W. Means Each Way
  5. Use the Callout to Count How Many Bars You Need

The worked example in the course applies this lesson to a realistic job in 6 steps, from "Decode the callout" through "Length in plan".

What you'll be able to do

  • Explain the main idea of "Reading a Rebar Callout" in plain language you can use on the exam.
  • Apply this step with confidence: "Decode the Spacing - O.C. Means Center to Center".
  • Apply this step with confidence: "Decode the Direction - E.W. Means Each Way".
  • Apply this step with confidence: "Use the Callout to Count How Many Bars You Need".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
READING A REBAR CALLOUTSlab Plan Note: "#4 rebar @ 12" O.C. E.W."12" O.C.12" O.C.E.W. = Each Way (both directions)#4bardiameter = 1/2 inchKEY FACT (Caltrans 52-1.04)Bar number = diameter ineighths of an inch.#4 = 4/8" = 1/2"#3=3/8" #4=1/2" #5=5/8" #6=3/4" #8=1"Source: 2025 Caltrans Std Spec §52-1.04 bar table; "on center": 2025 CRC R403.1.3.1CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: A Callout Packs Three Facts Into One Line

A structural plan note like "#4 rebar @ 12\" O.C. E.W." is shorthand that packs three separate facts into one short line: what size bar to use, how far apart to place it, and which directions to run it. 2025 CBC 1901.5 requires the construction documents for structural concrete to show the size and location of structural elements, reinforcement and anchors (item 3), and a callout like this is how a plan does it for a slab or wall. Decode each piece separately and the whole callout becomes simple.

Step 2: Decode the Bar Number - Nominal Diameter in Eighths of an Inch

The 2025 Caltrans Standard Specifications, Section 52-1.04, print a table of deformed bar designation numbers with nominal diameters: #3 = 0.375 in, #4 = 0.500, #5 = 0.625, #6 = 0.750, #7 = 0.875, #8 = 1.000 (and #9 = 1.128, #10 = 1.270, #11 = 1.410). Its note says bar numbers approximate the number of eighths of an inch in the nominal diameter, so #4 is 4/8 = 1/2 inch and #6 is 6/8 = 3/4 inch. The residential code uses the same designations, written "No. 4" (for example 2025 CRC R403.1.3.1 calls for not fewer than one No. 4 vertical bar).

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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