Scale, dimensioning and drawing conventions

Scale decides what a reader can see. Dimensions decide what a reader can build. Conventions decide whether two readers see the same thing. Get the first wrong and the set is hard to read. Get the second wrong and the shop builds the wrong size. Get the third wrong and the shop and the reviewer argue about a line.

This chapter covers all three. The numbers come from the Architectural Woodwork Institute's submittal standard, AWI 100, a published casework specification, a basic drafting handbook, the US National CAD Standard and NIST. The examples come from two real sets in hand, including two dimension strings that do not close.

Scale

How to read a scale

An imperial scale says how many inches on paper stand for one foot of the real thing. At 1/2"=1'-0", half an inch on the sheet is a foot in the room, so the drawing is 1/24 of full size. A metric scale is a ratio: 1:20 means one unit on paper stands for twenty in the room.

The architect's scale rule reads the imperial scales directly. The basic drafting handbook in hand describes it: "major divisions on the scale represent feet; those divisions are subdivided into 12ths or 16ths". The engineer's scale is decimal: on its 10 scale there are ten graduations to the inch, on its 50 scale fifty. Use the architect's scale on millwork drawn in feet and inches.

Imperial scale	Ratio	Where it appears in the sets in hand
1/4"=1'-0"	1:48	AWI 100 minimum for a reference plan
3/8"=1'-0"	1:32	AWI 100 minimum for plans and elevations
1/2"=1'-0"	1:24	Residential set: plans and elevations
3/4"=1'-0"	1:16	Residential set: the free-standing bar
1"=1'-0"	1:12	Residential set: sections through tall units
1 1/2"=1'-0"	1:8	Residential set: most sections; AWI 100 section minimum
3"=1'-0"	1:4	AWI 100 detail minimum; one university specification's detail minimum
12"=1'-0"	1:1	AWI 100: trim and scribe profiles "in full-sized profile"

The ratio column is arithmetic: 12 divided by the inch value. Check it yourself when a sheet mixes systems.

Which scale for which view

Pick the smallest scale at which the smallest thing the reader needs is still clear. An elevation has to show every door, drawer and trim piece on a wall. A section has to show a 3/4" panel, the edge on it and the hinge in it. A detail has to show a rebate, a reveal or a moulding profile. Each step in means a larger scale.

The standard puts floors under that judgement. AWI 100 sets a "universal minimum scale" for each view (§3.2.3 b):

View	Ratio	Scale, as printed
Reference plan	1:50	6.4 mm [.250"] = 305 mm [12"]
Plan & elevations	1:20	9.5 mm [.375"] = 305 mm [12"]
Sections	1:10	38.1 mm [1.50"] = 305 mm [12"]
Details	1:4	76.2 mm [3"] = 305 mm [12"]

It also asks for trim and scribes "shown in full-sized profile" for casework (§3.2.3.1 b) and trim profiles "at full scale" for panelling and door assemblies (§3.2.3.2 c, §3.2.3.5 b).

A specification can go further. One university's casework section sets "Minimum Scale of Detail Drawings: 3" to 1'". Read the specification's submittals article before you pick a single scale. Chapter 9 shows where it sits.

Print the scale under every view

The residential set prints AS NOTED in the title block and the scale under every view title. That is the right pattern for a sheet with more than one scale. A single scale in the title block of a mixed sheet is wrong for every view but one.

The residential set writes its scales as 1/2"=12" rather than 1/2"=1'-0". Both mean the same. Pick one form per set.

Never make the shop measure a print

The Woodwork Institute's sample says on its cover that the minimum sheet size is 11" × 17". The PDF of that sample is letter size, 8.5" × 11". A scale rule laid on a printout of it gives wrong answers, because the sheet was reduced. Any PDF can be printed at the wrong size. So write every dimension the shop needs. A dimension that has to be scaled off the sheet is a dimension you did not draw.

Dimensioning

Units and format

The two sets write dimensions differently:

• Residential: all inches, fractions, no inch marks. 196 3/8, 82 1/2, 20 7/16. Even a 64 1/2" height stays in inches.
• Woodwork Institute sample: inch marks on most figures, 21 3/4", 118 1/2". One of its bundled job sheets uses feet and inches, 2'-6". Its own sheet 9 marks cabinet heights as bare numbers in boxes: 82, 52, 32.5, 6.

Any of these works if the whole set uses it. What fails is a set where 30 means inches on one sheet and 2'-6" appears on the next. State the unit in the general notes if the figures carry no marks.

Which way the text reads

The drafting handbook names two systems. Unidirectional: every dimension reads from the bottom of the sheet, "typical for manufacturing drafting". Aligned: dimensions follow their dimension line and read from the bottom or the right side, "typical for architectural drafting". Both sets in hand are aligned: vertical heights read from the right side of the sheet.

Size and location

The handbook splits dimensions into two jobs: size dimensions give how big a thing is, and location dimensions give where it sits. A cabinet width is size. The distance from a wall to a sink centre is location. Every item on an elevation needs both. A shelf pin hole with a size and no location cannot be drilled.

The handbook also gives spacing for dimension lines on a plotted sheet: the first line 0.5" from the view, each further line 0.375" apart, and as many dimensions as possible between views rather than outside. That keeps strings readable at any scale, because the spacing is measured on paper, not in the room.

Strings that close

A dimension string is a row of part dimensions with an overall beside it. The parts must add up to the overall. This is the most important check in the chapter, and the easiest to skip.

Here are three strings from the Woodwork Institute's sample and its bundled job sheets. All three close:

String	Parts	Sum	Overall
Storage wall	1 1/2 + 21 3/4 + 36 + 36 + 21 3/4 + 1 1/2	118 1/2	118 1/2" — closes
Lounge top	1/2 overhang + 36 + 36 + 1 1/2	74	74" top — closes
Food lab, west	23 1/8 + 2 7/8 + 48 + 2 7/8 + 23 1/8	100	100" — closes

Here are two from the residential set. Neither closes:

Sheet	Parts	Sum	Overall printed	Gap
06, study wall	17 13/16 + 18 + 18 1/4 + 18 1/4 + 18 + 17 13/16	108 1/8	109	7/8
02, bar wall in plan	6 + 82 1/2 + 6 + 95 + 6	195 1/2	196 3/8	7/8

From the PDF alone, nobody can say which number is wrong. It could be a part, the overall, or a dimension whose text was typed over in CAD. That is the problem. The shop cannot tell either, and whoever cuts the parts decides alone. Chapter 23 covers what happens next.

Two habits prevent it:

• Never type over a dimension. Let the software measure. If the number looks wrong, the geometry is wrong. Fix the geometry.
• Add every string by hand before you issue. Fractions trip mental arithmetic. Convert to sixteenths, add, convert back.

Chain and running dimensions

A chain string gives each part end to end, like the strings above. It tells the shop the size of each box. A running or datum string measures every point from one reference, such as the floor or one end wall. It tells the installer where each thing sits, and errors do not stack up along the run.

Millwork elevations use both. Widths run as chains along the bottom, with an overall. Heights run from the floor as a datum. The Woodwork Institute sample draws horizontal dashed lines across its elevations at cabinet heights, each labelled with a number: 6, 32.5, 52, 82. One bundled job sheet marks backing centre lines at 31", 60", 75" and 86", and a counter "shim to 34" max A.F.F." AWI 100 asks for exactly this: blocking locations "shown on cabinet elevations with dimensions above finished floor (A.F.F.)" (§3.2.3.1 f).

Clear dimensions and field conditions

Some dimensions are about the gap, not the part. The residential set dimensions an appliance opening as 21 3/4 CLEAR wide and 34 CLEAR high, with the note "verify fitment". A clear dimension tells the shop what must stay empty. Use it wherever something made by someone else has to fit: appliances, sinks, equipment.

Dimensions taken from the architect's drawings are assumptions until someone measures the site. Mark them. An outsourcing vendor's article describes the contractor's part in validating "Verified-In-Field (VIF) dimensions". One published casework specification requires the shop to "field measure conditions where woodwork is indicated to be fitted to other construction" and to "show final field measurements on shop drawings". Where the floor may not be level, say how it will be taken up. A bundled job sheet in the sample carries a note: "4" high toekick may increase w/ shimming depending on job site floor conditions."

What goes on the elevation, what goes on the section

Both sets split the numbers the same way:

On the elevation	On the section
Overall length of each run	Depth of each cabinet
Width of each cabinet, filler and end panel	Material thicknesses: top, sides, back, bottom
Counter, upper and tall cabinet heights from the floor	Drawer box heights and inside clear widths
Openings for appliances and equipment	Top overhang and edge profile
Blocking and backing heights A.F.F.	Base or toe height and setback
Section callouts	Hardware type and position

AWI 100 lists what casework drawings must carry: "dimensions necessary to construct cabinets", the "type and thickness of drawer members (including heights and depths)", door type and thickness, "a section of each cabinet type or configuration", joinery and connections, and "provision for field dimensions" (§3.2.3.1 b–d). If a number is on both views, it must match. If it can live on one, keep it on one.

Tolerances

The drafting handbook says that "in most blueprint systems", a fractional dimension implies ±1/64". That is a manufacturing convention for machined parts. Do not assume it on millwork. Millwork tolerances come from the grade named in the specification, and chapter 20 covers them. Where a fit matters, write the tolerance on the drawing. One published casework specification does this in words: scribe casework "with maximum gaps of 1/32"".

Lines and views

The handbook's "alphabet of lines" is the shared language. The ones a millwork set uses most:

Line	Looks like	Used for
Object	Thick, solid	Every visible edge
Hidden	Thin, short even dashes	Edges behind a surface: a drawer box behind a front, a shelf behind a door
Centre	Thin, long and short dashes	Centre of a hole, a sink, a backing line
Phantom	Thin, one long and two short dashes	Alternate positions and absent parts: an appliance by others, an open door
Dimension, extension, leader	Thin, solid	Numbers and notes. Extension lines stop short of the object.
Break	Zigzag on a thin line	A long run shortened to fit
Section lining	Thin parallel hatching	Cut surfaces, with a pattern per material
Cutting plane	Heavy, with arrows and letters	Where a section is taken

The sample uses a hidden line for exactly the case the handbook describes, with a note: "dotted line is where drawer occurs". Both sets also draw diagonal lines across door fronts on their elevations. Neither set carries a legend saying what they mean. The National CAD Standard's abbreviations guidance says to put the list of abbreviations on the General sheets; a symbols legend belongs there too.

The handbook also notes that the United States and Canada use third-angle projection, with the top view above the front and the right side to its right, while "most of the rest of the world" uses first-angle, which swaps them. A drawing from a European hardware maker or a metric job may use the other arrangement. Check the projection symbol before you read a side view.

Abbreviations and symbols

The standard's rules

The National CAD Standard's Terms and Abbreviations module is blunt: "It is not the objective of the Module to encourage the use of abbreviations." Its guidelines:

• "Do not abbreviate words of five letters or fewer, except in schedules."
• "Avoid the use of abbreviations with more than one meaning."
• "Show the source or a list of abbreviations on the General sheets."
• "When the meaning of an abbreviation is in doubt, spell it out!"

What the sets actually use

Abbreviations that appear in the sets in hand, with their meanings where the set makes them clear:

Abbreviation	Meaning	Seen in
TYP.	Typical: applies at every like location	Both sets
A.F.F.	Above finished floor	AWI 100; sample job sheet
O.C.	On centre	Sample
ADJ. SH.	Adjustable shelf	Both sets
B/O, BY OTHERS	Supplied by another trade	Both sets
N.I.C.	Not in contract	Sample specification sheet
E.B.	Edge band	Sample specification sheet
SIM.	Similar	Sample job sheet
VIF	Verified in field	Singh article
CLEAR	Clear opening	Residential set

Now the problems. The sample writes plastic laminate three ways: L/P on its specification sheet, P/L on an elevation, and P.L. on a section. A reader can work it out, but the standard's rule is one term, one abbreviation. The residential set calls up #2 BASE, #4 MOULDING and #4 TRIM. Those are the shop's own profile numbers. Nothing in the 16 sheets says what profile #4 is. Inside the shop, everyone knows. The reviewer approving the look does not.

Metric and imperial

The fixed point

One inch is exactly 25.4 mm. NIST states that the inch, "derived from the value of the Yard effective July 1, 1959, is exactly equivalent to 25.4 mm". Every conversion starts there.

How the standard handles both

AWI 100 "is written with the metric system of measurement followed by the U.S. Customary System of measurement in brackets" (§3.1 a). The customary figure "is typically a 'soft' conversion": under 6", rounded to the nearest 0.1 mm; above 6", to the nearest 1 mm (§3.1 c). That is why its table reads 9.5 mm [.375"]: 0.375 × 25.4 is 9.525, rounded.

Where sets go wrong at the boundary

• Scales do not convert. 1/2"=1'-0" is 1:24. It is not 1:20 or 1:25. A metric reviewer who reads "half-inch scale" as 1:20 will misjudge every size on the sheet. Write the ratio beside an imperial scale on a job that crosses systems.
• Fractions do not round-trip. A 5 mm dimension is 0.197". The nearest sixty-fourth is 13/64", which is 5.16 mm. Convert a metric hardware dimension to a fraction, then back, and it has moved. Keep hardware dimensions in the unit the manufacturer publishes.
• Sheet size names do not agree. The drafting handbook calls 18" × 24" a "C" sheet and 24" × 36" a "D" sheet. The National CAD Standard's mock-up figure calls 34" × 44" "ANSI D". Two sources in hand, two different "D" sheets. Name a sheet by its size in inches or millimetres, as AWI 100 does: "279 mm x 432 mm [11″ x 17″]".
• One primary unit per set. A Revit template checklist from one design studio sets project units to "Millimeters (0 decimal places) for precision joinery" and names millwork views at 1:20. That suits a metric job. On an imperial job, pick inches. If the set must show both, follow AWI 100: primary first, secondary in brackets, everywhere.
• Projection may change too. See third-angle and first-angle above.

What to check before you issue

• Every view prints its scale, and each scale meets the minimum in the specification or AWI 100, read in the job's unit system.
• Profiles and scribes are drawn full size where the standard asks.
• Every dimension string adds up to its overall. Checked by hand, in sixteenths.
• No dimension text is typed over.
• Every item has a size and a location. Heights run from the floor.
• Blocking and backing heights appear on elevations A.F.F.
• Assumed dimensions are marked; field-verified ones say so.
• Clear openings are dimensioned for everything supplied by others.
• One unit format across the set, stated if the figures carry no marks.
• Every abbreviation and house code is defined in a legend, or spelled out.
• On a job that crosses systems: ratios beside scales, hardware in its own unit, sheet sizes in real dimensions.

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Sources

• Architectural Woodwork Institute, AWI 100 – Submittals, §3.1 a–e, §3.2.3 b–c, §3.2.3.1 b–f, §3.2.3.2 c, §3.2.3.5 b, awinet.org, read 21 September 2026. Minimum scales table, full-size profiles, measurement system and soft conversion, least-restrictive rule, sheet size in both units, casework dimension requirements, blocking A.F.F. Primary.
• NIST, "SI Units – Length", nist.gov/pml/owm/si-units-length, read 21 September 2026. The inch is exactly 25.4 mm, effective 1 July 1959. Primary.
• National Institute of Building Sciences, US National CAD Standard v6, UDS Module 5 §5.1 (abbreviation rules) and Module 2 §2.4 (mock-up sheet sizes, "ANSI D 34" x 44""), nationalcadstandard.org. Primary.
• Student Handbook for Basic Drafting (research/ptech_drafting_handbook_new.pdf). Architect's and engineer's scales, alphabet of lines, aligned and unidirectional dimensioning, size and location dimensions, dimension spacing, the ±1/64" fractional convention, first- and third-angle projection, sheet size names. Written for general and manufacturing drafting, not millwork. Document (textbook).
• University of Texas at Dallas, Design Guidelines, Section 06 41 00 Architectural Wood Casework, issued 21 June 2011. 3"=1' minimum detail scale, field measurements shown on shop drawings, 1/32" maximum scribe gap. Document.
• Woodwork Institute, Sample Shop Drawings and bundled job sheets. Closing dimension strings, height datum lines, backing centre lines A.F.F., shim and toe-kick notes, hidden-line note, abbreviations including three forms for plastic laminate, letter-size PDF against the 11" × 17" minimum. Document.
• A residential millwork submittal, 16 sheets. Scales as printed, inch-only dimension format, the two strings that do not close, CLEAR dimensions, "verify fitment", undefined house profile numbers. Not reproduced: live job. Document.
• Ripudaman Singh, "Essential Details You Should Look For in Millwork Drawings", hitechdigital.com, 2 July 2024 — an outsourcing vendor's blog. VIF dimensions and who validates them. Claimed.
• Albe Studio, Revit Architecture & Interiors Template Checklist v01. Millimetres at 0 decimal places; millwork views named at 1:20 — one studio's template advice. Claimed.