Dimensioning

Dimensioning is the orderly placement of measurements on a drawing so that the people building from it never have to guess. A dimension is made of extension lines, a dimension line, a terminator (arrow, tick or dot) and the figure itself. On a plan, dimensions are usually set out in strings from the outside in: the overall length first, then grid spacings, then openings and wall thicknesses closest to the building.

What good dimensioning looks like

A well-dimensioned sheet does the arithmetic for the builder. No size appears twice, the strings add up to the overall figure, and every chain is tied back to a grid line or a fixed surface. It should be obvious whether an opening is given as a structural size or a finished size. In sections and elevations, heights are mostly shown with level markers, and as the scale grows in detail drawings, millimetre figures take over.

• Text sits clear of the lines and reads in the expected direction.
• The unit is stated once on the sheet, usually centimetres or millimetres.
• The density of dimensions follows the drawing scale.

From drawing to model

Most 3D models begin from dimensioned sheets. Consistent figures mean fewer questions and fewer revisions once visualization starts. For more on how exterior drawings carry this information, see our piece on exterior architectural drawings.