Dimension Units

The millimeter is the common unit of measurement used on engineering drawings made to the metric system. The conventions used when specifying dimensions in metric units are discussed below.

1. When a metric dimension is a whole number the decimal point and zero are omitted.

(eg.) “12”

2. When a metric dimension is less than one millimeter, a zero precedes the decimal point.

(eg.) “0.3”

3. When a metric dimension is greater than a whole number by a fraction of a millimeter, the last digit to the right of the decimal point is not followed by a zero.

(eg.) ”13.2”

4. Where unilateral tolerancing is used and either the plus or minus value is ‘0’, a single ‘0’ shall be shown without a ‘+’ or ‘-‘sign for the zero part of the value.

(eg.)

5. Where bilateral tolerancing is used, both the plus and minus values have the same number of decimal places, using zeros where necessary.

(eg.)

6. Where limit dimensioning is used and either the maximum or minimum value has digits following a decimal point, the other value has zeros added for uniformity.

(eg.)

7. Angular Dimensions are established in degrees or decimal degrees, or in degrees, minutes and seconds.

(eg.) 250, 7.50, 300 15’ 30”

8. Where a dimension is less than one degree, a zero precedes the decimal point

(eg.) 0.50

9. Where only minutes or seconds are specified, a zero precedes the minutes and seconds.

(eg.) 00 15’ 30”

10. Where only whole number angle degree is specified, the value is followed by a degree symbol. A zero or decimal point is not shown after the degrees.

(eg.) 300

In industry a general note would be given on the engineering drawing to invoke the metric system. 

MILLIMETERS”