What is an AutoCAD CTB file?

An AutoCAD CTB file (Color-Dependent plot style Table) is a file that controls how colors are printed or plotted in an AutoCAD drawing. CTB files map AutoCAD color indexes to lineweights, screening, plot style colors, and linetype scale so you can get consistent printed output from drawings that use color for on-screen clarity.

What is a CTB file and why it matters

• CTB = Color-Dependent Plot Style Table. It ties an AutoCAD color index (ACI 1–255) to specific pen settings (lineweight, color, screening, linetype).
• Use CTB files when you want print output based on object color rather than on named styles or per-object overrides.
• Typical uses: monochrome printing, ensuring specific lineweights on output, or matching a printer/plotter workflow that expects color-to-pen mappings.

Key concepts (quick explainer)

• Color-dependent: CTB maps by the object’s color (ACI). If a drawing uses named plot styles (STB) or objects are set to use named styles, CTB rules do not apply.
• Lineweight control: Assign thicker or thinner printed lines based on color, independent of on-screen appearance.
• Monochrome output: A CTB can force all colors to print in black (or another color) and with defined weights.
• Plot style types: CTB (color-dependent) vs STB (named plot styles). They are mutually exclusive in a single drawing — you use one system or the other.

Where CTB files are stored

Common locations (replace version/year with your installation):

• User plot styles folder: %appdata%\Autodesk\AutoCAD \Rxx.x\enu\Plotters\Plot Styles\
• Program folder: C:\Program Files\Autodesk\AutoCAD \Plotters\Plot Styles\

If AutoCAD can’t see a CTB file, place it in one of these folders and restart AutoCAD.

How to load and apply a CTB file — step by step (beginner-friendly)

1. Save or copy the .ctb file into your AutoCAD Plot Styles folder (see locations above).
2. Open the drawing in AutoCAD.
3. Open the Plot dialog:
   • Type PLOT and press Enter, or click the Plot icon.
4. In the Plot dialog find Plot style table (pen assignments) (often a dropdown).
5. Select the desired .ctb file from the list. If it does not appear, use the folder icon or place file in the Plot Styles folder and restart AutoCAD.
6. Make sure the checkbox Plot with plot styles (or similar option) is checked — CTB files only take effect when this is enabled.
7. Click Preview to confirm output looks as expected, then OK or Plot.

To assign a CTB to a layout permanently:

1. Right-click the layout tab → Page Setup Manager → Modify.
2. In the Page Setup dialog choose the CTB under Plot style table and click OK.

How to create or edit a CTB file

1. In the Plot dialog, next to the Plot style table dropdown, click Edit (or open Plot Style Manager from the AutoCAD menus).
2. This opens the Plot Style Table Editor.
3. Select a color (1–255) and set:
   • Color (what the pen prints as),
   • Lineweight (the printed thickness),
   • Screening (percent transparency on print),
   • Linetype and other options.
4. save as a new CTB or overwrite an existing one.
5. Apply the new CTB in the Plot dialog or Page Setup.

Alternative methods and workflows

• Use STB (Named Plot Styles) if you prefer assigning styles by name (easier for some CAD standards and for objects that aren’t colored via ACI).
• Use Page Setup templates to standardize CTB usage across multiple drawings.
• For PDF output, select your PDF driver in the Plot dialog and choose the CTB in the same way — CTB mapping works with most plotters and PDF drivers.
• Use the command CONVERTPSTYLES to convert drawings between color-dependent (CTB) and named plot styles (STB).

Common problems and how to fix them

Problem: CTB file not listed in Plot dialog

• Fix: Place the .ctb file in the AutoCAD Plot Styles folder (see locations above). Restart AutoCAD if needed.

Problem: Plot styles not applied / objects still print in color

• Fix: Ensure Plot with plot styles is checked in the Plot dialog or Page Setup. Confirm objects are using ACI color values (not necessarily TrueColor or by-layer if you intended CTB mapping).

Problem: Lineweights look wrong on print

• Fix:
  • Verify the CTB assigns the intended lineweight to the color.
  • In the drawing turn on lineweight display to preview.
  • Confirm the plotter/paper scale and plot parameters are correct.

Problem: Monochrome prints gray instead of black

• Fix: In the CTB set the pen color to black and screening to 100% (no screening). Also check PDF viewer color settings and plotter driver options.

Problem: Mixing CTB and STB in a drawing

• Fix: A drawing uses either CTB or STB. Use CONVERTPSTYLES to convert if you must switch systems. Remove named plot styles or color-dependent table as appropriate.

Problem: Duplicate CTB names or wrong version used

• Fix: Remove duplicate CTB files from other Plot Styles folders, keep only the intended one, and restart AutoCAD.

Practical tips and best practices

• Keep a central Plot Styles folder for office standards and instruct users to place CTB files there.
• Name CTB files clearly (e.g., OfficeName_Monochrome.ctb, A1_PlotWeights.ctb) for easy selection.
• Use Page Setup templates that reference a CTB to maintain consistency across sheets.
• Use Preview in the Plot dialog before final plotting.
• Document which color → lineweight mapping your CTB uses for team members.
• When collaborating, include the CTB file with the drawing package or store it in a shared network location.

FAQ

What is the difference between CTB and STB?

CTB (Color-Dependent Plot Style Table) maps print styles by color index (ACI). STB (Named Plot Styles) assigns named plot styles directly to objects or layers. You can use one system per drawing; use CONVERTPSTYLES to switch.

My CTB file isn’t showing up — what should I check first?

Make sure the .ctb file is in AutoCAD’s Plot Styles folder (user or program folder). Restart AutoCAD if necessary. Also verify you are looking at the correct Plot Styles folder for your AutoCAD version.

Do CTB files affect on-screen colors?

No — CTB files control printed/plot output, not how colors appear on screen. They assign printed pen colors, lineweights, and screening based on object colors.

Can I force everything to print black using a CTB?

Yes. Create or use a CTB (for example, Monochrome.ctb) that maps all colors to black and set screening to 100%. Also ensure Plot with plot styles is enabled.

How do I convert drawings that use CTB to STB?

Use the AutoCAD command CONVERTPSTYLES to convert color-dependent plot styles to named plot styles (or vice versa). Back up drawings before converting.

Why do my lineweights look different between printers?

Plotters and PDF drivers can interpret pen settings differently. Check the CTB pen assignments, the plotter’s driver settings, paper size and scale, and preview before final output.

Can CTB handle TrueColor or indexed color books?

CTB works with AutoCAD ACI (color indexes). TrueColor objects may not map reliably to ACI. If your drawings use TrueColor heavily, consider converting those colors to ACI or using STB named styles.

Where should I store CTB files for a team environment?

Store CTB files in a shared network Plot Styles folder and instruct team members to copy or map to that location, or place the CTB in the company standard installation folder so AutoCAD finds it automatically.