Rebar Size Converter
Look up rebar bar numbers and their diameter in inches, millimeters, and cross-sectional area.
Select a bar size for full details.
Select a rebar size — see diameter, area, and weight details.
Rebar (reinforcing bar) sizes use a numbering system based on diameter.
US bar sizes (imperial):
- Bar number = diameter in 1/8 inch increments
- Example: #4 bar = 4/8 inch = 0.5 inches diameter
Common rebar sizes:
| Bar # | Diameter (in) | Diameter (mm) | Area (in2) | Weight (lb/ft) |
|---|---|---|---|---|
| #3 | 0.375 | 9.525 | 0.11 | 0.376 |
| #4 | 0.500 | 12.700 | 0.20 | 0.668 |
| #5 | 0.625 | 15.875 | 0.31 | 1.043 |
| #6 | 0.750 | 19.050 | 0.44 | 1.502 |
| #7 | 0.875 | 22.225 | 0.60 | 2.044 |
| #8 | 1.000 | 25.400 | 0.79 | 2.670 |
| #9 | 1.128 | 28.651 | 1.00 | 3.400 |
| #10 | 1.270 | 32.258 | 1.27 | 4.303 |
| #11 | 1.410 | 35.814 | 1.56 | 5.313 |
Metric rebar uses the diameter in mm directly (e.g., 10M = 10 mm).
The elegance of the imperial system is that the number is the size: a #4 is 4/8 inch, a #8 is a full inch, so you never need a chart to know the diameter. Metric keeps it even simpler by naming the bar after its millimeter diameter outright.
The trouble starts when a project mixes drawings from both systems, because the bars don’t line up one-to-one. A #4 (12.7 mm) and a 10M (10 mm) sound close but differ in cross-sectional area, and area is what actually carries load. Reinforced concrete is engineered around the total steel area in a section, so substituting a near-size bar quietly changes the strength of the structure. When converting, match on diameter and area rather than a number that merely looks similar, and when in doubt follow the engineer’s spec, not what happens to be on the truck.
How we build and check this converter
This converter runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.