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Choosing the Right Font for Optimal Medical Device Usability

Don’t overlook these important factors.

Image courtesy of StarFish Medical

Choosing the right font, size, color, and spacing not only defines aesthetic design but also has a profound impact on the usability of the medical device you are developing. This can affect components such as Graphical User Interfaces, Instructions for Use, and labels that often contain important information.

When we determine the usability of text material, three factors play a key role: legibility, readability, and comprehension.


Legibility is the ease with which a reader can recognize individual characters. Font size, line height, and line length can affect a user’s ability to see, distinguish, and recognize each character and words. If users are squinting, holding the material closer, or commenting that it’s difficult to read, then the legibility is poor.

HE75 contains a good guidance on font size in relation to various viewing distances and angles.

High color contrast between the text and background is good for legibility. Avoid busy or textured backgrounds.


Readability is the quality of being easy to read. The readability of text depends on the complexity of the vocabulary, syntax, and presentation. 

Readability of a material is presented as a Nth grade reading level. For example, an 8th grade reading level means that a person who has completed an 8th grade education can easily read the text. Microsoft Word has a useful tool for checking the reading level.

Balanced color contrast is best for readability. High contrast black text on a white background is helpful for users who are prone to skimming instead of reading carefully. But high contrast can cause eye strain if read for an extended period. The same is true of white text on a black background. White has 100% color brightness, and black has 0%. The large contrast in light level means that the eyes need to work harder to adapt.

A balanced contrast such as dark gray text on white background has better readability than black on white. If you are designing a screen to be used in a setting where the lights are intentionally kept off or low, you may not want to use a white background as the screen will emit lot of light. A light gray text on dark background might be more appropriate.


Reading comprehension is the ability to process and understand the meaning of the text read. The text must guide the intended user to understand the meaning and draw the intended conclusion. When it comes to instruction manuals or action-oriented content in a GUI, we want the users to perform the correct actions after reading the text.

It is important to test the comprehension of the text by conducting usability studies with the intended user groups. You must ensure the users can comprehend and carry out the instructions correctly.

Serif vs Sans Serif Fonts

Which type of font should you use?

A serif is the short line stemming from the end of a stroke of a letter.  (See below.)

The most recognizable serif font is probably Times New Roman.

Sans serif fonts on the other hand do not have the extending features at end of strokes. Arial is a frequently used sans serif font.

Best Fonts for Print

Grab any book, newspaper, or magazine nearby. Most likely, the inside content will be a serif typeface. For printed materials, it’s widely accepted that serif fonts are easier to read. Serifs make the letters flow together. Therefore, they are easier to transition from one letter to the next.

Serif fonts are for "readability," while sans serif fonts are for "legibility." That is why sans serif are often used for headlines and serif for the body text.

A book titled Cashvertising cites a 1986 study, where three different fonts were tested for reading comprehension: two serifs (Garamond and Times New Roman) and one sans serif (Helvetica). They found 66% comprehended Garamond, 31.5% Times New Roman, and 12.5% Helvetica (out 1,010,000 people surveyed).

The participants who read the sans-serif version said they had a tough time reading the text and repeatedly had to go back to regain comprehension.

Best Fonts for Digital

What works on a printed paper does not always work on a digital screen.

A high degree of resolution is required to legibly render a serif font. A screen resolution of 800 x 600 pixels is not great for displaying the details of serif fonts; therefore, simple sans serif fonts are recommended. In 1996, Microsoft introduced Verdana as one of the first fonts designed for on-screen legibility. Since then, they have introduced more elegant and screen-friendly fonts such as Calibri.

If you are designing a medical cart with a high-resolution large screen monitor, legibility shouldn’t be a problem for serif typefaces (if using an appropriate font size). If you visit popular news and magazine websites such as NBC, ABC, Fast Company, and Forbes, you will see both serif and sans serif being used for the body text. Thus, for high-resolution screens you have more freedom to make the font choice based on aesthetics.

Designing for Seniors

It’s very common for people to experience decreased contrast sensitivity, inability to focus, and visual field loss as they age. recommends a minimum of 12 point text with 14 points of leading (explained below). Keep in mind some fonts are smaller than others. For example, 12 point Times New Roman is smaller than 12 point Verdana.

Spacing is important for legibility to all ages but especially for seniors as characters and lines of text may seem like they are blending with each other. Different types of spacing to consider are listed below (and shown in the image at top):

  • Leading: Vertical spacing between the lines.
  • Kerning: Horizontal spacing between a pair of letters.
  • Tracking: Horizontal spacing between all the letters in a large block of text.

When it comes to color, high contrast is helpful for seniors. Because many seniors experience decreased contrast sensitivity, high color contrast is not perceived as eye straining and it helps separate the text from the background.


Many different elements can influence the usability of a text. After designing text material with the appropriate font, size, spacing, and colors, don’t forget to verify the legibility, reading level, and comprehension by testing the material with intended user groups.

Christine Park

Christine Park

Christine Park is an industrial designer at StarFish Medical, a medical device design company headquartered in Victoria, British Columbia. She believes that product design has the power to change a society’s behavior. She uses her knowledge of color, material, and finish to design innovative and empathetic medical devices.

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