# Dimensioning

The dimension describes the dimensions of a single part or an assembly . Dimensions are given in numerical values on technical drawings or in CAD programs (2D, 3D). To this end, the following specifications must be observed:

• The unit of measurement generally used ( millimeter , also meter in architecture ) does not have to be specified.
• The actual numerical value is called the nominal dimension .
• The nominal dimension can, however, be provided with various additions such as tolerances and fits . Preceding characters indicate that the dimension is a diameter (Ø), a radius (R), a spherical shape (S), an arc (Bg) or a square cross-section (a square in front of the size of the font used) acts.
• If no further additions are added to the nominal dimension, a general tolerance that is specified in the title block applies .
• An underlined dimension indicates that the drawing deviates from the dimension figure at this point.
• A frame around the dimension defines that this dimension is of particular importance and must be checked after production.

## Dimensioning in construction drawings

In construction drawings , the dimensions have a special feature: All dimensions under 1 meter are given in the unit of centimeters on the dimension lines, dimensions over 1 meter in the unit of meters , without this being specifically marked. The units can be distinguished from the fact that all measurements from one meter always have a comma with two decimal places, possibly also two zeros after the decimal point, and that centimeters never have a comma symbol. Thus the dimension “50” means 50 cm; the dimension "50.00" means 50 m. Millimeters are always added to the dimension as a small exponent and usually rounded to 5 mm. Length measurements are always above a dimension line. Dimension entries below a dimension line indicate the clear height of window and door openings. The parapet height is shown with the prefix BRH = directly at the respective opening.

Dimension chains are placed around the floor plan on the edge of the sheet, the labeling is legible from below for horizontal dimension lines and from the right for vertical dimension lines. The limits of the dimensions on the chains consist of short lines at right angles to the dimensional chain and optionally a point at the intersection of the lines or another short diagonal line that always points upwards to the right in relation to the dimension line. In contrast to other technical drawings, the boundary lines of the individual dimensions of a dimensional chain are not extended to the component. Arrows as delimitation are unusual, as is the interruption of the dimension line in order to insert the dimension number in between at the same height.

In addition to the dimensions on the dimension chains, there are other dimensions that are entered when dimensioning a drawing. These include details of the level marks as the finished floor level ( FFL ), the upper edge of soffit ( OKRD ), etc. of a projectile, which are registered with the respective abbreviations and symbols directly at a suitable point in the drawing.

The display methods are specified in the drawing standards (including DIN 406 dimension entry in drawings ).

Drawings from CAD systems often deviate from these standardized representation methods that are common in Germany and instead use the simplified American conventions.

## literature

• Hans Hoischen, Wilfried Hesser: Technical drawing . 30th edition. Cornelsen Verlag, Berlin 2005, ISBN 3-589-24110-1 .
• Ulrike Portmann, Dieter Portmann: Symbols and symbols in architectural drawings according to standards. 5th edition. Wiesbaden; Berlin: Bauverlag 1993, ISBN 3-7625-2982-5
• Ernst Neufert: building design theory. Manual for construction professionals, builders, teachers and students. Friedr. Vieweg & Sohn Verlag / GWV Fachverlage GmbH, Wiesbaden 2005, ISBN 3-528-99651-X