Basic Dimensioning
How to annotate simple drawings for
use in constructing an object
Learning Objectives



Be able to understand the basic rules of
dimensioning
Apply dimensions to objects in accordance
with engineering standards
Define the following items: Dimension line,
Extension line, Reference dimension, and
Leader
2
Basic Dimensioning



Dimensions allow a part to be manufactured
Dimensions are ALWAYS in real world units
Dimensions should be applied in a concise,
coherent manner
3
Dimension Terminology:
DIMENSION LINE
EXTENSION LINE
ARROWHEAD
3.00
1.80
.80
.90
1.00
EXTENSION LINE:
EXTENSION
LEADER
GAP
2.00
1.00
1.20
4
Extension lines
Extension lines
should be offset
from the part by
one half the text
height and should
extend one text
height beyond the
dimension line
5
Dimension Spacing
The first row of
dimensions must be
a minimum of 3 text
heights away from
the part.
Any dimensions
beyond it must be a
minimum of 2 text
heights apart
6
Arrowheads:
Should be 3 times longer than they are wide.
7
Dimensioning Rules



Avoid placing any dimensions
on the part (inside the view)
unless there is no other option.
Always place the dimension
where the characteristic shape
is shown in the most
descriptive view. (This means
don’t place a dimension on
object lines making a “T joint”.)
Always dimension holes in
their circular view by stating
the diameter of drilled holes.
Specify the hole depth of
special features such as
countersinking with a note
following the dimension.



Dimension cylindrical objects
as diameters in their
rectangular view.
Keep dimensions between the
views whenever possible
Extension lines may cross
each other and over other lines
on the part, but dimension
lines should never be crossed.
See Essentials of Engineering Design Graphics Chapter 4
8
Dimensioning Rules




Do not duplicate dimensions
and avoid using unnecessary
or superfluous dimensions
For metric drawings, omit the
use of the millimeter (mm)
notation following the numeral,
as millimeters are the default
units.
Dimension rounded corners
and arc features as radii where
they appear in their rounded
views.
Avoid dimensioning to hidden
features.



Extend leaders from the first of
last word in a note. Point them
toward the center of circular
features that they are
specifying.
Place dimensions among the
various views to avoid
crowding. Stagger horizontal
dimensions to avoid contact or
crowding of values.
The overall dimension should
always be given. It should be
placed outside of smaller
dimensions and be the furthest
dimension from the part.
See Essentials of Engineering Design Graphics Chapter 4
9
1. Avoid placing dimensions on the part (inside of the
view).
See Essentials of Engineering Design Graphics Chapter 4
10
2. Avoid dimensioning to hidden features
There is one
exception:……
When the hidden
line is a finished
(√) surface
See Essentials of Engineering Design Graphics Chapter 4
11
3. Always place dimensions where the characteristic
shape is shown in the most descriptive view
See Essentials of Engineering Design Graphics Chapter 4
12
4. Always dimension holes in their circular view with
the Ø. Specify special features (hole types) with a
note.
Also:
Remember to
locate hole
position with
ordinate
dimensions to
hole centers
See Essentials of Engineering Design Graphics Chapter 4
13
5. Dimension rounded corners and arc features as
radii where they appear in their rounded view.
See Essentials of Engineering Design Graphics Chapter 4
14
6. If the same value is repeated many times, then use a
general note for the feature.
(ALL FILLETS AND ROUNDS ARE .125R)
See Essentials of Engineering Design Graphics Chapter 4
15
7. Dimension cylinders in their rectangular view
with a diameter symbol….Ø.
See Essentials of Engineering Design Graphics Chapter 4
16
8. Place the first row of dimensions 3 text heights
(3/8 ”or 10 mm) away from the edge of the part.
Additional stacks
of dimensions can
be a minimum of
two text heights
(1/4 ”or 6 mm)
away from each
other
See Essentials of Engineering Design Graphics Chapter 4
17
9. Keep dimensions between views whenever
possible .
See Essentials of Engineering Design Graphics Chapter 4
18
10. Extension lines may cross each other and over
other lines on the part, but dimension lines should
never be crossed. (Hint no “arrow-headed” lines can
cross “arrow-headed” lines)
See Essentials of Engineering Design Graphics Chapter 4
19
11. The overall dimension should always be given. It
should be placed outside of smaller dimensions and
be the farthest from the part.
See Essentials of Engineering Design Graphics Chapter 4
20
12. Do not duplicate dimensions and avoid using
unnecessary or superfluous dimensions
See Essentials of Engineering Design Graphics Chapter 4
21
15. For metric dimensions less than 1 mm DO place a
zero in front of the decimal point.
See Essentials of Engineering Design Graphics Chapter 4
22
16. For metric drawings, omit the use of the
millimeter (mm) notation following the numeral, as
millimeters are the default units.
See Essentials of Engineering Design Graphics Chapter 4
23
18. Conserve space and time by using abbreviations
and standardized symbols whenever possible.
See Essentials of Engineering Design Graphics Chapter 4
24
20. Extend leaders from the first or last word in a
note. Point them toward (but not touch) the center of
the circular features that they are specifying.
See Essentials of Engineering Design Graphics Chapter 4
25
21. Place dimensions among the various views to
avoid crowding. Stagger horizontal dimensions to
avoid contact or crowding of the values
See Essentials of Engineering Design Graphics Chapter 4
26
Angular features:
Dimension angular features with either:
X,Y coordinate location
or
Vertex location & degrees
See Essentials of Engineering Design Graphics Chapter 4
27
Dimension Styles
Unidirectional dimensions Aligned dimensions align
are read from the lower left with individual dimension
lines.
corner of the sheet
See Essentials of Engineering Design Graphics Chapter 4
28
A short review on Dimension “elements”
•What is…
•an Extension line ?
•an Extension line gap ?
•an Extension line extension ?
•a Dimension line ?
•a Dimension numeral ?
•a leader ?
•When are…
•Decimals used ? Not used ?
•Unit designators (in. or mm) listed on dimension
lines ?
•What size…
•Is an Arrowhead ?
29