Keep chart text at or above 9 pt / 12 px

Set every chart text element to at least 9 pt / 12 px. For example, keep only minor text such as axis labels at 9 pt, and make other chart text larger than that minimum.

Small chart text is harder to discriminate and read, so labels and other chart text become less accessible, especially for readers with low vision.

Mechanism: Raising text to at least the minimum size improves legibility and reduces the chance that readers miss or struggle to read chart text.

Evidence: Chartability treats small text as a critical perceivable failure and states that text must not be smaller than 9 pt / 12 px, with only minor text ideally rendered at that minimum (Elavsky et al., 2022). The linked research summary reports that text smaller than about 9 pt significantly reduces readability and reading speed, supporting that threshold for chart labels and annotations (Arditi, 2017).

Notes: The 9 pt / 12 px threshold is a minimum, not a default size for all text.

• User Goal: Read chart text directly from the visualization.
• Chart Setting: The visualization includes rendered text, and its font size can be set or reviewed.
• Audience: Readers include people with low vision.
• Success Criterion: No chart text is smaller than 9 pt / 12 px, and only minor text sits at that minimum.

Break it when: the rendered font size cannot be determined from design specs, code, or metadata. Why: the source says font-size testing is highly complex and difficult without that information, so compliance cannot be verified reliably.

Sacrifice: Font-size review becomes a manual audit task when size is not stored or documented. Risk: Visual spot checks can misjudge whether text actually meets the minimum. Mitigation: Keep font sizes available in design specs, code, or metadata so reviewers can verify them.

Mistake: Using 9 pt / 12 px as the default size for all chart text. Why it fails: the source defines that size as the minimum and says only minor text should ideally be rendered at that size.

Failure Sign: Any chart text is smaller than 9 pt / 12 px. Quick Check: Inspect code, design specs, or metadata for font-size values and flag anything below the minimum. Stronger Test: If size data is missing, confirm the rendered font size with the designer or developer instead of relying only on visual estimation.

• Increase any chart text below 9 pt / 12 px until it meets the minimum.
• Keep only minor text, such as axis labels, at 9 pt / 12 px.
• Increase other chart text beyond the minimum instead of leaving it at 9 pt / 12 px.
• Record font sizes in design specs, code, or metadata so the chart can be audited reliably.