Construction Knowledge Series: Guide to Rebar Sizing

In blueprints and specifications, rebar size is always called out by number without any other descriptions as to the size of the rebar.  For those who are not in the concrete or rebar industry, rebar numbering and sizing can seem intimidating.  However, standard rebar numbering is pretty straight forward once you know how the sizing works.

Rebar sizing up to a #8 Rebar is done in increments of 1/8” diameter.  1/8” and 1/4" would be fairly inconsequential so standard rebar starts at 3/8” diameter => #3 Rebar.  This simple system is incredibly useful when onsite and trying to determine what size rebar you are looking at.  If your tape measure says 3/4" diameter, you are dealing with #6 bar.  1/2" diameter => #4 bar. 

The 1/8” increments end at #8 bar, but the rule closely approximates #9 bar (1.128” diameter) and #10 bar (1.27” diameter).  If you encounter rebar larger than 1.27” diameter, just know that it’s big and track down your nearest ironworker to tell you what you’re dealing with.

Try to see if you can determine the rebar size number the next time you come across a piece of rebar.