Application of Dimensions

  1. Dimension Lines
  2. Extension (Projection) Lines
  3. Limited Length or Area Indication
  4. Leader Lines
  5. Reading Direction
  6. Reference Dimensions
  7. Overall Dimensions
  8. Dimensioning Within the Outline of a View
  9. Dimensions Not to Scale

Dimensions are applied by means of dimension lines, extension lines, chain lines, or a leader from a dimension, note, or specification directed to the appropriate feature. See Fig. 1-6. General notes are used to convey additional information. For further information on dimension lines, extension lines, chain lines, and leaders, see ASME Y14.2.

Dimension Lines

A dimension line, with its arrowheads, shows the direction and extent of a dimension. Numerals indicate the number of units of a measurement. Preferably, dimension lines should be broken for insertion of numerals as shown in Fig. 1-6. Where horizontal dimension lines are not broken, numerals are placed above and parallel to the dimension lines.

NOTE: The following shall not be used as a dimension line: a center line, an extension line, a phantom line, a line that is part of the outline of the object, or a continuation of any of these lines. A dimension line is not used as an extension line, except where a simplified method of coordinate dimensioning is used to define curved outlines. See Fig. 1-35


Dimension lines shall be aligned if practicable and grouped for uniform appearance. See Fig. 1-7.


Dimension lines are drawn parallel to the direction of measurement. The space between the first dimension line and the part outline should be not less than 10 mm; the space between succeeding parallel dimension lines should be not less than 6 mm. See Fig. 1-8.

NOTE: These spacings are intended as guides only. If the drawing meets the reproduction requirements of the accepted industry or military reproduction specification, nonconformance to these spacing requirements is not a basis for rejection of the drawing.

Where there are several parallel dimension lines, the numerals should be staggered for easier reading. See Fig. 1-9.

Angle Dimensions.

The dimension line of an angle is an arc drawn with its center at the apex of the angle. The arrowheads terminate at the extensions of the two sides. See Figs. 1-3 and 1-6.

Crossing Dimension Lines.

Crossing dimension lines should be avoided. Where unavoidable, the dimension lines are unbroken.

Extension (Projection) Lines

Extension lines are used to indicate the extension of a surface or point to a location preferably outside the part outline. See para. 1.7.8. On 2D orthographic drawings, extension lines start with a short visible gap from the outline of the part and extend beyond the outermost related dimension line. See Fig. 1-8. Extension lines are drawn perpendicular to dimension lines. Where space is limited, extension lines may be drawn at an oblique angle to clearly illustrate where they apply. Where oblique lines are used, the dimension lines are shown in the direction in which they apply. See Fig. 1-10.

Crossing Extension Lines.

Wherever practicable, extension lines should neither cross one another nor cross dimension lines. To minimize such crossings, the shortest dimension line is shown nearest the outline of the object. See Fig. 1-9. Where extension lines must cross other extension lines, dimension lines, or lines depicting features, they are not broken. Where extension lines cross arrowheads or dimension lines close to arrowheads, a break in the extension line is permissible. See Fig. 1-11.

Locating Points or Intersections.

Where a point is located by extension lines only, the extension lines from surfaces should pass through the point or intersection. See Fig. 1-12.

Limited Length or Area Indication

Where it is desired to indicate that a limited length or area of a surface is to receive additional treatment or consideration within limits specified on the drawing, the extent of these limits may be indicated by use of a chain line. See Fig. 1-13.

Chain Lines

In an appropriate view or section, a chain line is drawn parallel to the surface profile at a short distance from it. Dimensions are added for length and location. If applied to a surface of revolution, the indication may be shown on one side only. See Fig. 1-13, illustration (a).

Omitting Chain Line Dimensions

If the chain line clearly indicates the location and extent of the surface area, dimensions may be omitted. See Fig. 1-13, illustration (b).

Area Indication Identification.

Where the desired area is shown on a direct view of the surface, the area is section lined within the chain line boundary and appropriately dimensioned. See Fig. 1-13, illustration (c).

Leader Lines

A leader is used to direct a dimension, note, or symbol to the intended place on the drawing. Normally, a leader terminates in an arrowhead. However, where it is intended for a leader to refer to a surface by ending within the outline of that surface, the leader should terminate in a dot. A leader should be an inclined straight line except for a short horizontal portion extending to the mid-height of the first or last letter or digit of the note or dimension. Two or more leaders to adjacent areas on the drawing should be drawn parallel to each other. See Fig. 1-14.

Leader-Directed Dimensions

Leader-directed dimensions are specified individually to avoid complicated leaders. See Fig. 1-15. Where too many leaders would impair the legibility of the drawing, letters or symbols should be used to identify features. See Fig. 1-16.

Circle and Arc

Where a leader is directed to a circle or an arc, its direction should be radial. See Fig. 1-17.

Reading Direction

Reading direction for the following specifications apply:


Notes should be placed to read from the bottom of the drawing with regard to the orientation of the drawing format.


Dimensions shown with dimension lines and arrowheads should be placed to read from the bottom of the drawing. See Fig. 1-18.

Baseline Dimensioning

Baseline dimensions should be shown aligned to their extension lines and read from the bottom or right side of the drawing. See Fig. 1-50.

Feature Control Frames

Feature control frames should be placed to read from the bottom of the drawing.

Datum Feature Symbols

Datum feature symbols should be placed to read from the bottom of the drawing.

Reference Dimensions

The method for identifying a reference dimension (or reference data) on drawings is to enclose the dimension (or data) within parentheses. See Figs. 1-19 and 1-20.

Overall Dimensions

Where an overall dimension is specified, one intermediate dimension is omitted or identified as a reference dimension. See Fig. 1-19. Where the intermediate dimensions are more important than the overall dimension, the overall dimension, if used, is identified as a reference dimension. See Fig. 1-20.

Dimensioning Within the Outline of a View

Dimensions are usually placed outside the outline of a view. Where directness of application makes it desirable, or where extension lines or leader lines would be excessively long, dimensionsmay be placed within the outline of a view.

Dimensions Not to Scale

Agreement should exist between the pictorial presentation of a feature and its defining dimension. Where a change to a feature is made, the following, as applicable, must be observed.

(a) Where the sole authority for the product definition is a hard-copy original drawing prepared either manually or on an interactive computer graphics system, and it is not feasible to update the pictorial view of the feature, the defining dimension is to be underlined with a straight thick line. Where a basic dimension

(b) Where the sole authority for the product definition is a model (digital), refer to ASME Y14.41.

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