Staalgoed Handel B.V.

Converting rebar from imperial sizes (US) to European metric sizes

15-02-2024 | M.E. de Jong

Sometimes we receive projects where the diameters of rebar are shown in imperial diameters (US diameters). For these projects, we convert the imperial diameters to metric units. Below this text, you can easily download the table.


American/imperial sizing for rebar indicates diameter in units of 1⁄8 inch (3.2 mm) for bars from size #3 to #18. Where #8 equals 8 x 1⁄8 inch = 8⁄8 inches, or 1 inch (25 mm) diameter.

Some imperial sizes are not available such as #12-13, and #15-17, for example.

The "#" symbol stands for the number sign. In other words, "#6" means "number six". Use of the "#" symbol is common for US sizes, but sometimes "No." is used.

Substituting imperial measurements for metric units

When US/imperial sizes for rebar are used on the drawing, while metric rebar should be used in the project, you want to convert the sizes. How do you go about this?

First, a practical example to make things a bit clearer. If you look in the table at #9, "soft metric" will be No.29. "Hard metric" becomes D32. This is because this is a metric available rebar diameter.

Soft metric

When you convert the imperial diameter (#) to the metric size of the rebar (No.) it is called the soft metric. There is usually no bar available whose diameter is literally the number of millimetres it says in the column of the US nominal diameter converted to the metric value in mm.

Hard metric

The bars you actually convert to, i.e. the available metric sizes that is the 'hard conversion' also called 'hard metric'.

When you choose a higher available rebar diameter, you make the safe choice.

Useful table

For converting imperial diameters to the metric system, we have developed a table so that we do not have to calculate for each project.

We are happy to make this table available to you. You don't have to leave your e-mail address to download the table. Feel free to also share it with others who may benefit from it.

Download table for converting imperial (US) to (European) metric sizes 

 US rebar size chart