Text sizes and standards in a technical drawing [Complete guide]

Every engineer, architect, and designer has encountered the frustration of squinting at technical drawings with illegible text.

While modern CAD software allows easy zooming on screen, the real test comes when drawings are printed.

Whether working on A0 or A4 paper, proper text sizing ensures your technical communication remains clear, professional and unambiguous.

So, understanding and implementing standard text sizes in technical drawings is crucial for effective project communication.

This comprehensive guide explores the principles and practices that ensure your technical drawings stay professional and meet industry standards.

The Foundation: Readability and Legibility

Technical drawing text serves two primary functions that must work in harmony.

Readability and Legibility.

Readability involves the strategic choice of words and symbols to communicate information efficiently.

For instance, expressing a gradient as “1:20” rather than “1 unit change in every 20 units change” saves valuable drawing space while maintaining clarity.

Legibility determines how comfortably text can be read at various distances and scales.

This aspect becomes critical when drawings are printed and viewed without the luxury of digital zoom capabilities.

The industry standard establishes a minimum text height of 3 mm (0.12″) as the baseline for clear communication.

But that’s not the only parameter you should consider, there are several other factors as well that influence text legibility in technical drawings.

Font style plays a crucial role, with simple, clean typefaces proving most effective.

Font size must balance space constraints with readability requirements.

Line weight affects text prominence and hierarchy.

Contrast between text and background ensures visibility under various lighting conditions.

Finally, paper size determines the practical limits of text reduction while maintaining legibility.

So, let’s talk about all of these parameters one by one.

Recommended Text Sizes:

Different standards and common practices provide specific text height recommendations for various elements on a drawing to ensure legibility, even if printed at half scale.

Metric Standards (ISO, BS):

The BS Standards define eight nominal lettering heights: 1.8, 2.5, 3.5, 5.0, 7.0, 10, 14, and 20 mm, calculated using a 1:√2 (≈ 1:1.4) formula, similar to paper sizes and line weights.

Essentially, each height is roughly √2 times the previous size.

As an example 1.8 mm × √2 ≈ 2.5 mm, 2.5 mm × √2 ≈ 3.5 mm, 3.5mm × √2 ≈ 5.0mm, and so on.

This method ensures that each larger letter is easier to distinguish and remains visually proportional to others which creates consitency in technical drawings.

1.8 mm:

Standard metric text heights of 1.8 mm (or sometimes 2.0 mm)  is used sparingly, primarily when standard text height won’t fit.

2.5 mm: 

The standard, general-purpose text height for almost everything, such as notes, dimensions, and elevations.

This is also recommended as a minimum for A1, A2, and A3 paper sizes for notes and dimensions.

3.5 mm: 

This text size is used for secondary titles (like SECTION A-A), schedule or table titles.

It is recommended for titles on A1, A2, A3, and notes/dimensions on A0 paper sizes.

5.0 mm: 

This text size is used for primary titles like ‘TYPICAL’, ‘FLY’, ‘BRACE’, ‘DETAIL’, drawing titles, axis numbering, and section letters. 

It is recommended for headings on A1, A2, A3, and titles on A0 paper sizes.

7.0 mm: 

This one is obviously used for big titles, often used on cover sheets or in the title block text. 

It is recommended for headings on A0 paper size.

For A3 size sheets, 2mm high text is suggested, while for sheets larger than A2 (A1, A0, B1), 2.5mm high text is recommended as a minimum, especially if the drawing might be printed at half scale.

The following table illustrates these text size standards for metric unit.

Imperial Standards (US Standard/ANSI):

3/32″ (approximately 0.09375″ or 2.5mm) is the minimum acceptable text size for technical drawings in US federal and military contracts, as it remains legible if the drawing is printed at half size.

Many firms use this for normal text, notation, and leaders.

1/8″ (approximately 0.125″) is a commonly required standard for most jurisdictions in the US.

Some designers use it if 3/32″ receives complaints.

However, using 1/8″ for everything can look “goofy big”.

Apart from that a 9 pt (9/72″ or 0.125″) looks good for important notes and 3/16″ is commonly used for titles.

For key text in title blocks, like the sheet title and sheet number, sizes like 0.18″ to 0.2″ are suggested.

So to summarize it all…

• 5 mm to 7 mm (3/16″ to 1/4″) is recommended for title block headings (e.g., project title, drawing number).

• 3.5 mm to 5 mm (1/8″ to 3/16″) is recommended for drawing labels (e.g., plan titles, section heads).

• 2.5 mm to 3.5 mm (3/32″ to 1/8″) is recommended for general notes, dimensions, and labels.

The following table illustrates these text size standards for imperial unit.

Font Types

Now let’s talk about the next imporatnt feature of text in technical drawings which can impact legibilty of the drawing and it’s font type.

Commonly used fonts for technical drawings include Arial, Tahoma, Simplex, Roman, TXT, ISOCP, ISOCPEUR, and Helvetica.

No matter what font you are using it is crucial to use the same font consistently across the entire drawing.

For example, in your company you can make a standard practice to use Arial for title block text and Simplex for all remaining drawing text.

Also stick with Sans Serif fonts for clarity as they don’t look cramped even when text size is small.

Following illustration shows differnce between serif and sans serif font.

Text Placement and Formatting

Now let’s talk about the way text should be added in the draiwng and it’s formatting settings.

Notes and Annotations: 

Notes are used to simplify or complement the graphic presentation. 

They should be stated in the present tense, in imperative or permissive mood, and lengthy, complex, or indefinite notes should be avoided.

General notes refer to the part or drawing as a whole and should be placed centrally below the relevant view or in a general note column.

Local notes apply to specific local requirements and are connected by a leader line to the feature.

Dimensions: 

When dimensions include subscripts or superscripts (such as in tolerances), some ISO formats render these as very small characters.

For better readability, tolerances should ideally use the same font size as the associated dimension.

Alignment:

Text is typically left-aligned for general notes, right-aligned for dimension strings, and title block information is often centered.

Structure you should follow in a drawing

When it comes to the design and presentation, there are various factors that you should consider and understand the reason behind the different sizes within the same document.

Irrespective of the of the discipline that one is working in, when it comes to final presentation of technical designs a title block is usually used.

A title block, as shown above, is a section of the sheet that provides details about the design, including the drawing or illustration, related notes, information about the depicted items, and details of the drafter, designer, company, checker, and others involved.

There are different considerations for the different sections of a title block which I have mentioned below:

Title:

This text is usually the largest to convey what the drawing’s subject matter is all about.

Subtitles and Section Headings: They are smaller than the main title, but they are still easy to single out.

They usually communicate what each viewport has in the drawing.

Dimensions:

They indicate the measurement of different components in the drawing as e.g. length, degrees, etc.

The font is usually dependent on the part of the dimension; if it is the overall dimension, the font is bolder and more legible compared to the break dimensions.

Notes and Specifications:

This is used to convey crucial information about the components in the drawing, such as the materials used, the main parameters to be considered, etc.

The font size is usually smaller than the above three, as it is usually considered as fine print.

Call out and Leader’s line text:

These are used to mark or tag different components in the drawing that can now be captured in the Notes area.

The font used should be clear and legible, avoiding any overlapping of text in every single area of the title block.

Compliance with Industry Standards

National standards bodies like ANSI, ISO, BS, JIS, and AS/NZS publish specific guidelines for text height and formatting.

Adhering to these standards is essential for professionalism and meeting client or regulatory requirements.

The BS Standards define a range of eight nominal lettering heights: 1.8, 2.5, 3.5, 5.0, 7.0, 10, 14, and 20 mm, which are calculated using a 1:√2 formula as mentioned previously in the article.

Federal and military contracts mandate, a minimum of 3/32″ text size, Local building departments mandate text size of 1/8″, some companies may enforce their own text size standards.

So, you should know these standards and adhere to them.

This demonstrates that external requirements can override internal preferences when it comes to text standards.

It also highlights how firms establish specific font standards for different elements of a drawing to maintain consistency and professionalism.

Mistakes you should avoid

Now that we know about the standards let’s talk a little bit about common mistakes that you should avoid in your technical drawings.

Mistake 1: Using Too Many Text Sizes, making drawings look cluttered and inconsistent.How to avoid: Limit yourself to three standard text sizes (commonly 2.5mm for notes and details, 5mm or 7.5mm for titles and section letters) throughout the drawing.

This keeps annotations clear and professional.Mistake 2: Using multiple fonts or switching between cases within the same drawing, leading to poor legibility and a non-unified appearance.How to avoid: Use the same font (preferably Arial or simplex) throughout your drawing, and always write text in CAPITAL letters.Mistake 3: Selecting text that is too small, which becomes illegible when the drawing is printed, scaled down, or viewed digitally.How to avoid: Never use text smaller than 2.5mm for general notes or labels.

Always test the legibility of your smallest text by printing or viewing the drawing at the intended reproduction scale.Mistake 4: Overloading the drawing with excessive text, symbols, or notes, making key information hard to locate.How to avoid: Prioritize essential information. Use part drawings or separate views to break up crowded areas. Keep annotations concise and focused.Mistake 5: Placing text on inappropriate or merged layers, which complicates edits and can make it difficult to distinguish different types of annotation.How to avoid: Always organize text on dedicated annotation layers to streamline collaboration and future modifications.Mistake 6: Not Using Annotative Styles and manually scaling text for each viewport, resulting in mismatched sizes between different drawing views.How to avoid: Use annotative text styles in CAD software so your text automatically scales correctly based on the viewport or paper size.

Most CAD software uses the Annotative scaling option that allows the text and other annotations to appear with a consistent size regardless of the viewports, as shown in the illustration below.

Here is a table summarizing these common mistakes and what you can do to avoid them.

Frequently Asked Questions

Before I wrap up here are some frequently asked questions that I see quite often.

Question: What is the minimum text size for technical drawing as per ASME?

Answer: The minimum text size for ASME technical drawings according to the ASME Y14.2 standard is 0.12 inches (3 mm) in height for dimensions and notes within the drawing. 

This size ensures legibility and reproducibility of technical information on the drawing though in some cases users may use slightly larger sizes depending on the drawing scale or format.

Question: What is the standard text height in AutoCAD drawings?

Answer: There is no fixed universal “standard” text height in AutoCAD, but the default starting size is often around 0.12 inch or 3 mm for MTEXT if you use default template.

The size of text however varies from template to template and you can customize it as well in text style settings.

Question: What is the standard text size for architectural drawings?

Answer: The minimum standard text size for architectural drawing is typically 1/10 of an inch or 0.1 inch.

This size ensures legibility when drawings are reduced in size.

Other frequently used size for architectural drawings are 1/10″, 1/8″, 5/32″, and 3/16″.

This is about 2.5 mm for general notes and dimensions, and up to five mm or more for headings and titles.

Summary

Improper text scaling undermines both the clarity and accuracy of technical documentation.

Adhering strictly to standardized text sizes and consistent scaling methods ensures professional, readable, and reliable drawings that reduce errors and improve efficiency in technical workflows.

So, in summary:

• You should use only standard font heights like 1.8–20mm for ISO/BS standard and 2.5 mm range for ANSI and ASME standard.

• Stick to one font, sans-serif and monospaced where possible examples are Arial, Simplex, and ISOCP.

• Limit to three text sizes per drawing for hierarchy.

• Never drop below minimum standards for note or label size.

Did we missed anything that should be added in the article? Let me know in the comments down below.