Good drawing practice is demonstrated on the sample
Several questioned our use of mm for large dimensions.
drawings in this document.
In response, we have utilized both m and mm in
specifications in the interim period, and have found little
Centimeters shall not to be used.
difficulty or confusion using either.
Dual dimensions shall not be used.
Our new general rule is to use m or mm, whichever you
Example, 200 mm (7-7/8")
Dual dimensions are a complete waste of time in
Concrete to be 200 mm thick. (0.2 m could be used)
construction documents. When english units are there,
readers use them and ignore the metric.
Clearance shall be 1500 mm. (1.5 m could be used)
Use preferred scales:
This practice differs from drawing usage where mm are
1:1 1:2 1:5 1:10 1:20 1:50 1:100 1:200 1:500 1:1000
used exclusively in many areas.
Many state DOTs use 1:250 for urban plan sheets.
In specifications, the unit (ex, m or mm) is almost
always present. Little room exists for confusion. On
ISO Paper Sizes are the standard international paper
drawings, using mm eliminates the need to write m or
sizes, and are often available within a few weeks,
mm, and eliminates decimal usage for all but large scale
anywhere in our country, from domestic sources.
civil and road design drawings.
Many state and federal agencies, such as Army Corps,
Centimeters should not be used. A small class of items
Huntsville Division, are now using them.
reference standards using cm or cm2, such as fire ratings
for some products. These areas only, which account for
We are now generating designs in this region around A1
less than 2 % of specification references, should make
size. Designs are to now use ISO sizes, see below.
reference to cm or cm2.
The Government Printing Office now stocks A4 paper
It is recommended that each region establish a directory
for purchase by other agencies.
of pure SI specifications, as we have done, and not mix
SI and english specifications.
Many state highway groups have adopted A1 as their
standard drawing size.
It is also not recommended to have both metric and
english in a guide specification section, as this requires
A0 1189 x 841
A3 420 x 297
spec writers to edit english out of the document.
A1 841 x 594
A4 210 x 297
Nominal Technique Many spec references can
A2 594 x 420
effectively use nominal mass, nominal volume, or
nominal length technique. Ex, if 1 gallon of product x is
required (or, 3.785 L) the spec could be rewritten using
nominal volume, requiring 4 L (+/- 0.25 L). People can
then say 4 L when referencing this item, yet still allow
current product to be submitted.