Post 602 by Gautam Shah 



These are rules per ISO, and also better methods of writing measurements on DESIGN RELATED DRAWINGS. These apply to manual drawings and also CAD representations.

All decimal numbers must be preceded by a zero if no other digit exists. e.g. 0.121 (and not as .121 )

No thousand or hundred markers are to be used, e.g. 1000 (and not 1,000), but where large number of digits are involved a blank or space (equal to 1 digit or not less than ½ digit in width) may be used as a separator, in place of a marker. However, where only four digits are used no space as a separator need be provided. e.g. 100 000, 10 000 or 1000 (but not 1 00 000 or 1 000).

▪ For Length units recognized measures are km / m / mm which may if at all required must be in small letters. For example architectural plans have nearly all measures in mm, so the mention of mm should be avoided. However, in the same drawing if weight or volume or such other measures are to be indicated, then identifiers for such units may be indicated.


Architectural drawings nominally have dimensions of maximum 5 digits (for mm ) unless a detail requires indicating a fraction of a millimeter, signifying measures up to 99999 mm or 99.999 mts (-but unit identifiers are not to be used). Plans larger then 99mts sizes are considered of Map Category.

▪ Full names of units even when these are named after a person, are written in small letters: ampere, volt etc., with the exception W for watt and J for Joule.

▪ For liquid measure (Litre) however lt may be written as Lt (to differentiate between 1 and l ).

▪ Plurals of measures need not be used. (kms, mts, kgs).

Point or Full stop for abbreviation may not be used, for example as in m.g. or ml.

▪ Where cubic or square measures are to be shown: 3m3 = will mean three cubic metres and not 33 i.e. 3 x 3 x 3 = 27cmt.

▪ Following common units are acceptable

Length  mm m  km (all 1000 factored=103)

Weight  gm  kg  mt or t (all 1000 factored=103)

Liquid  mlt  Lt  klt (all 1000 factored=103).


Where traditionally only one unit is accepted, and if there are no chances of ambiguity, the measure nomenclature (mm, km, gm etc.) may not be mentioned. (E.g. cloth width = 1.200). If in one sheet of drawing (or a document) only one scale and one mode of measure are used, the nomenclature may be mentioned as a general instruction for the drawing.

Where drawings or details are likely to be graphically reduced or enlarged in processing / copying, a graphical scale preferably showing 100 mm bar may be shown. If 100 mm size is not suitable due to micro reduction or macro enlargement, suitable multiples of 100 mm for upwards scaling and 10x fractions of 100 mm for downwards scaling maybe used.



When both mt & mm are used on drawings, it will be less confusing if the dimensions are always written to three places of decimals, i.e. 3.450. No unit symbol need be shown unless a lesser number of decimal places are used; i.e. 3.450 or 3.45 m and under some circumstances 3.5 m, are all correct. Of the options, 3450 and 3.450 both are preferred. Where no ambiguity can arise, symbols may be discarded, according to following rules:


▪ Whole numbers indicate mm

▪ Decimated fractions to three palaces of decimals indicate m (and also by implication, mm)

All other dimensions or measures must be followed by the unit symbol.

▪ Where dimensions refer to different types of measures (lengths, weights, temperature etc.), preferably all units should be indicated or all units other than the major one should be indicated.

▪ Main dimensions and the tolerance (fitments, limits, margins etc.) etc. should be in the same unit system.

▪ Where main dimensions are accompanied by + or – range, both should be in the same unit.


All architectural drawings follow ISO modular preferences and these are as follows:

ISO’s Four Preferences for Modular Coordination:

       First Preference            30 cm or 300 mm = 12″

      Second Preference      10 cm or 100 mm = 4″

      Third Preference           5 cm or 50 mm = 2″

      Fourth Preference        2.5 cm or 25 mm = 1″

First Preference is favoured by the building materials’ industry. Plywoods and other wood products are available in modules of 300 such as 600, 900, 1200, 1800, 2400 etc. Large buildings are designed with 300 as the modular measure. But, for smaller spaces such as Bedrooms, toilets, second preference of 100 is used as a module.

Second Preference is considered to be the most appropriate one for Building components and Planning. Glazed Tiles are available in multiples of 100 mm, with sizes like 100 x 200, 200 x 200, 200 x 300 etc., and also in sizes such as 150 x 150, 150 x 200 etc. as a carry over from the old system. Fabrics have widths of 600, 900, 1000, 1200, 1800 etc. When we order Windows or Doors the width x height are measured in 100 mm increments.

Third and Fourth Preferences are more preferred for objects smaller then 300 sizes. These preferences are not to be used for basic object sizes of more than 300, unless there are strong economic or functional reasons for doing differently.