En Iso 13920-bf Jun 2026
Therefore, a callout of indicates that a workshop must meet medium precision constraints across all dimensional, angular, and geometric orientations. Linear Dimension Tolerances (Class B)
EN ISO 13920 is a European standard titled, "Welding — General tolerances for welded constructions — Dimensions for lengths and angles — Shape and position" . It is the European adoption of the international standard ISO 13920:2023, having been approved by CEN (European Committee for Standardization) without any modification. This standard is a critical tool in the manufacturing and engineering industries, as it specifies general tolerances for all welded structures, including weldments, welding assemblies, and other fabricated constructions.
Do you need help choosing between and a tighter standard like Class AE ? Share public link
To avoid disputes, the tolerance class should be a formal part of contractual agreements. The client should specify the required class in the Request for Quotation (RFQ), and the fabricator should price the work according to the effort required to achieve that precision. This practice sets clear expectations and creates a fair link between cost and accuracy. en iso 13920-bf
The first letter denotes the allowed variance for overall sizes, distances, step configurations, and intersecting weld corners. The standard defines four classes: : Fine B : Cool/Medium C : Coarse D : Very Coarse.
While Class B is versatile, it is not always the right choice.
Therefore, defines a "Medium-Medium" requirement—a standard level of precision suitable for general fabrication, where high precision is necessary, but not as extreme as specialized machinery. Scope of EN ISO 13920 The standard applies to: Therefore, a callout of indicates that a workshop
: Represents Medium Accuracy . This is the most widely assigned class for industrial equipment, general fabrication, and construction engineering. It balances reasonable workshop manufacturing costs with tight operational control.
For example, a 1,000 mm beam manufactured to Class B may allow a few millimeters of variation in straightness, whereas the same beam in Class A would demand significantly less. A steel plate with a nominal dimension of 2,500 mm and a specified flatness tolerance of Class F would allow a deviation of 6 mm across its length.
The component of EN ISO 13920-BF ensures that the final geometry of the assembly does not twist or bow excessively out of shape. These metrics dictate the maximum gap allowed between the surface of the weldment and a perfect reference plane or straightedge. Over 30 up to 120 mm : Maximum deviation of Over 120 up to 400 mm : Maximum deviation of Over 400 up to 1,000 mm : Maximum deviation of Over 1,000 up to 2,000 mm : Maximum deviation of Over 2,000 up to 4,000 mm : Maximum deviation of Over 4,000 up to 8,000 mm : Maximum deviation of Practical Implementation in Engineering Drawings This standard is a critical tool in the
To make this standard useful, we must look at the specific numerical allowances it grants. All tolerance tables in the standard are based on the "nominal dimension," which in the case of a length is the measured size, and for parallelism, it's the length of the shorter surface being measured.
Source: DIN EN ISO 13920 Standard.
A common way to denote general tolerances on an engineering drawing is to list them in the drawing's title block. A typical example is . This is a shorthand code that communicates a great deal of information to the manufacturer and quality control personnel.
Specifying acceptable deviation limits on drawings.
