New:

AEC definitions

What Are CAD Standards?

Last reviewed: November 2026

CAD standards are the rules a firm or client sets for how drawings are built: layer names, colors and line weights, text and dimension styles, blocks and symbols, title blocks, plot styles, and file and sheet naming. In the US, most firm standards build on the National CAD Standard, which includes the AIA CAD Layer Guidelines and the Uniform Drawing System.

Start for freeView use cases
1234567ABCLAB301LAB302LAB303LAB304LAB305LAB306LAB SUPPORT307OPEN LAB308LAB SUPPORT309LAB SUPP310LAB SUPPORT311STAIRS2301302303304305306P127'-3"27'-0"27'-3"27'-3"27'-0"27'-3"94'-8"1AFLOOR PLANSCALE: 1/8" = 1'-0"N1234CONSULTING ENGINEERSREVISIONSPROJECTWESTFIELD LABSSCALE1/8" = 1'-0"DATE09/15/2026KEY PLANSHEET TITLEFLOOR PLANSHEET NUMBERA-101

What you're looking at

Floor Plan, annotated

An architectural floor plan with walls, doors, room tags, and the column grid every other discipline draws on.

  1. 1Exterior wall with window openings
  2. 2Door, swing, and door tag
  3. 3Room name and number
  4. 4Partition type tag
US baseline
National CAD Standard version 6, from the National Institute of Building Sciences
Layer format
Discipline, major group, optional minor groups, optional status, such as A-WALL-FULL
Sheet numbers
Discipline, sheet type, and sequence, such as A-101 or E-601
Text
Fixed plotted heights, commonly 3/32 inch for notes
Plotting
Color-dependent CTB or named STB plot style tables
Delivered as
A manual, a DWT template, a DWS file, and block libraries

Definition

CAD standards

A CAD standard exists so that anyone can open any file and know where things are, and so that every sheet in a set plots the same way. It is usually a written manual plus template files: a DWT drawing template with layers and styles preset, a DWS standards file for checking, a CTB or STB plot style table, and libraries of blocks and title blocks. Owners such as universities, hospital systems, and federal agencies often impose their own CAD standard for record drawings, so a consultant may draft to the firm standard during design and convert to the owner standard at closeout.

In depth

Layer names encode discipline, content, and status

Under the AIA CAD Layer Guidelines, which the National CAD Standard incorporates, a layer name starts with a discipline designator, then a four character major group, then optional four character minor groups. A-WALL is architectural walls, A-WALL-FULL is full-height partitions, E-LITE is lighting, and M-HVAC-SUPP is supply ductwork.

An optional single character status field marks phase, such as N for new, E for existing to remain, and D for existing to demolish. With status on the layer, one background can produce both the demolition plan and the new-work plan by freezing and screening layers. Without it, someone redraws or sorts linework by hand for each plan.

Text and dimension styles control how a sheet reads

A standard sets text styles by plotted height and font, commonly 3/32 inch for notes, 1/8 inch for room names, and larger heights for titles, along with dimension styles for each discipline. Annotative styles in AutoCAD keep those plotted heights consistent across viewports at different scales.

Mixed styles are the clearest sign that content was copied from another project. A detail pasted in with its own dimension style may show arrowheads where the firm uses architectural ticks, or round dimensions to a different precision than the rest of the sheet.

Plot styles turn colors into line weights

With a color-dependent CTB table, the color of an object decides the pen weight and screening when the sheet plots, so color 1 might plot at 0.25 mm and color 8 at a halftone. With a named STB table, each layer or object is assigned a plot style by name instead. A drawing uses one mode or the other, and the CONVERTPSTYLES command switches between them.

Because plot styles live in a separate file, a drawing sent without its CTB plots with default weights. Consultants exchange the plot style table along with the backgrounds so screened architectural linework plots light under their own work.

Sheet and file naming make a large set navigable

The Uniform Drawing System numbers sheets by discipline, sheet type, and sequence. In A-101, A is architectural, 1 is the plans sheet type, and 01 is the sequence. Sheet type 5 is details and type 6 is schedules and diagrams, so E-601 is where a reader expects the panel schedules.

File naming rules do the same job for DWGs, so a background named for its level and discipline can be found and xrefed without opening a dozen files. Owners with document control systems often dictate this part of the standard.

A standard only holds if someone checks it

AutoCAD can compare a drawing against a DWS standards file with the CHECKSTANDARDS command, flagging nonstandard layers, line types, text styles, and dimension styles. The Layer Translator maps a consultant's layer names onto the firm's names in one pass.

Automated checks catch names. A door drawn on the wall layer, or a symbol exploded into loose lines, passes a name check and still breaks the set, which is why standards reviews also include a person looking at plotted sheets.

Examples

CAD standards on a real project

  • 01

    A consultant receives backgrounds layered to the architect's office standard and uses the Layer Translator to map them to NCS names before freezing furniture and screening walls.

  • 02

    A hospital system requires record drawings on its own layer list and title block, so the engineer converts the design DWGs to that standard at closeout.

  • 03

    A plotted electrical sheet shows heavy architectural walls under the power layout because the CTB file was not sent with the backgrounds.

Tooling

Drafting to your standard and checking against it

Nomic drafts in CAD using your layers, blocks, line types, text styles, dimension styles, and title blocks, and follows how your firm drew the same items on past projects. The DWG files it saves use the names your sets already use.

Nomic checks its own drawings against your standard and the code edition you name, clouds what it drew, and lists anything it could not match. Your team reviews the sheets, and the professional of record stamps them.

Best AI for CAD automation

Best AI for CAD Automation in 2026

FAQ

Frequently asked questions

The US National CAD Standard, published by the National Institute of Building Sciences, combines the AIA CAD Layer Guidelines, the Uniform Drawing System, and plotting guidelines into one standard for organizing building drawings. Version 6 is the current edition.

A layer name has a discipline designator, a four character major group, optional four character minor groups, and an optional status code, separated by hyphens. A-WALL-FULL is architectural full-height walls.

A CTB table assigns plot weights and screening by object color. An STB table assigns them by named plot styles attached to layers or objects. A drawing uses one mode at a time.

A DWS is an AutoCAD drawing standards file. It stores the layers, line types, text styles, and dimension styles a drawing should use, and the CHECKSTANDARDS command compares a drawing against it.

Keep reading

Related terms and workflows

What Is CAD in Architecture and Engineering?

CAD, short for computer-aided design, is software that architects and engineers use to draw buildings and systems precisely at full size, then lay those drawings out on sheets at a chosen scale for permit and construction. In building design, CAD usually means 2D drafting in a DWG-based program such as AutoCAD, with lines, blocks, layers, and text standing in for walls, equipment, and notes.

What Is a Title Block?

A title block is the ruled area on a drawing sheet, usually along the right edge or the bottom, that identifies the project, the sheet number and title, the author, the date, the scale, and the revision history. It is how you tell one issue of a sheet from another.

What Are Line Weights in Architectural Drawings?

Line weights are the different thicknesses of line used on a drawing to tell the reader what matters most. Heavy lines mark what is cut, medium lines mark visible edges beyond the cut, light lines show surface detail, and the finest lines carry dimensions, grids, and leaders.

Drafting to your CAD standards

Layers, blocks, and text styles applied the way your firm draws.

Sheet setup and title blocks

Layouts, viewports, and title blocks set up from your template.

What Are CAD Standards? | Nomic