Rebar Size Table
| Bar size | Soft metric | Nominal diameter | Diameter (mm) | Area (sq in) | Weight (lb/ft) |
|---|---|---|---|---|---|
| #2 | No.6 | 1/4 in | 6.35 | 0.05 | 0.167 |
| #3 | No.10 | 3/8 in | 9.53 | 0.11 | 0.376 |
| #4 | No.13 | 1/2 in | 12.7 | 0.20 | 0.668 |
| #5 | No.16 | 5/8 in | 15.9 | 0.31 | 1.043 |
| #6 | No.19 | 3/4 in | 19.1 | 0.44 | 1.502 |
| #7 | No.22 | 7/8 in | 22.2 | 0.60 | 2.044 |
| #8 | No.25 | 1 in | 25.4 | 0.79 | 2.670 |
| #9 | No.29 | 1.128 in | 28.7 | 1.00 | 3.400 |
| #10 | No.32 | 1.270 in | 32.3 | 1.27 | 4.303 |
| #11 | No.36 | 1.410 in | 35.8 | 1.56 | 5.313 |
| #14 | No.43 | 1.693 in | 43.0 | 2.25 | 7.650 |
| #18 | No.57 | 2.257 in | 57.3 | 4.00 | 13.60 |
Rebar numbers are a measurement in disguise: the bar number is the diameter in eighths of an inch. A #4 bar is 4/8 inch across - half an inch, the most common bar in the world - and a #8 is 8/8, a full inch. The chart carries that code in the diameter column and adds what the number alone cannot tell you: cross-sectional area (which is what the concrete actually feels) and weight per foot (which is what the delivery truck feels). Both matter when you translate a drawings list like 'twelve #5 @ 12 in each way' into tons of steel and a trip to the supplier.
Two quirks in the table are not typos. First, the code breaks at #9: a #9 bar measures 1.128 inches across, not 9/8 = 1.125, because from #9 up the standard lets diameter drift to keep the area ladder clean - the fraction-accurate bars are #2 through #8. Second, the metric column (No.10, No.13, No.25...) is a soft conversion, not a separate standard: No.25 just means 'about 25 mm', the rounding of 25.4 mm. Countries on true metric rebar roll different bars entirely. And the gaps are real: there is no #12, #13, #15, #16 or #17 - ASTM A615/A706 simply defines #2-#11, #14 and #18, sizes inherited from the square-bar era.
How to use
- Read the bar number as eighths of an inch to sanity-check any order: #3 is 3/8 inch, #5 is 5/8 inch, #8 is one inch. If the bar you received measures a different diameter, the number on the tag is wrong.
- Pick size by area, not by feel: the load calculations were done on the area column, so a substitution like #4 for #5 (0.20 to 0.31 sq in) gives 55% more steel - fine where extra steel helps, not fine when spacing was designed around exact area.
- Estimate delivery weight with the lb/ft column: a 20-foot stick of #4 weighs about 13 lb, a 60-foot bundle of ten #5 sticks about 1,040 lb. A half-ton pickup hauls roughly forty #4 sticks and not much more.
Frequently asked questions
What is the difference between #4 and #5 rebar?
Half an inch versus five-eighths of an inch in diameter - but the number that matters is area: #4 carries 0.20 square inches, #5 carries 0.31, a 55% jump. #4 is the default for driveways, patios, sidewalks and slab-on-grade work on a 12-to-18-inch grid; #5 is the step up for driveway edges that take vehicles turning, short retaining walls, and footings where the plan calls for it. Weight scales the same way - 0.67 versus 1.04 lb/ft - so a job quoted in tons swings fast when the plan upgrades. What does not change is the mating hardware: chairs, ties and mesh overlap rules mostly span both sizes, so the upgrade is about steel, not accessories.
Why is there no #12, #13, #15, #16 or #17 rebar?
Because the US standard only defines certain sizes: #2 through #11, then #14 and #18 - nothing between. The surviving big bars trace to the square-twisted-steel era, when 1 3/8-inch and 2 1/4-inch squares converted to the round bars we now call #14 and #18. The in-between numbers were never issued, so a plan that calls for #16 is either using metric designation (which countries with true metric rebar do have) or a typo. Practically, the ladder jumps are deliberate: #11 is the practical top of the stick-market range, and beyond it engineers move to bundles of smaller bars, which bond better in concrete than one giant bar anyway.
What do grade numbers like Grade 40, 60 and 75 mean?
They are yield strength in ksi - thousands of pounds per square inch the bar yields at - and they are independent of the bar number. Grade 60 (60,000 psi) dominates US construction; Grade 40 bends easier and shows up in light or historical work; Grade 75 heads into columns and heavy structural members. Grade is stamped in the bar's rolling marks alongside the size and mill, so a delivered bar announces both: bar size first (the eighths code), then the grade letter or number. When substituting between grades the areas stay identical - a #5 is 0.31 sq in whether it yields at 40 or 60 ksi - so upgrades trade strength per pound, not geometry, and the rebar-size table below still applies.
Is No.25 rebar the same as 25 mm rebar?
Not exactly - No.25 is a soft-metric label on the US #8 bar: 25.4 mm rounds to 25, so the bar is 'about 25 mm' across. The diameter column shows the honest number: 25.4 mm. True metric countries roll bars on their own size ladder with different areas and weights, and a No.25 US bar does not automatically match a 25 mm European bar in area or bond rules. The soft conversion exists so US drawings can carry metric-looking tags without re-engineering the whole standard - which is why the metric column on this page is labeled 'soft'. Reading the imperial number as eighths of an inch stays the ground truth: No.25, #8, one inch across, 0.79 square inches of steel.