ISO 24509:2019 PDF

Ergonomics — Accessible design — A method for estimating minimum legible font size for people at any age

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Title (English):

ISO 24509:2019

Ergonomics — Accessible design — A method for estimating minimum legible font size for people at any age

Document status:: Active
Format:: Electronic (PDF)
Number of pages:: 37
Publication date:: October 4, 2019
Edition:: ISO IS 24509 edition 1 version 1
ICS:: 13.180

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Description (English):

This document provides a method for estimating minimum legible font size for single characters, but not for words or sentences, in self-luminous or reflected mode, used in documents, products labels, signs, and displays for people at any age and in any viewing condition in which viewing distance, luminance and contrast are varied. This document applies designing and evaluating legibility of single characters for people at any age who have no pathological disorders in their eyes, but not for people with visual impairments such as low vision. The application is specifically directed to, but not limited to, the cases of printed materials where fixed font size is used. Applicability of the method to other languages is given in Annex F.

Technical details

Technical committee: ISO/TC 159/SC 4 - Ergonomics of human-system interaction
SKU: ISO 24509:2019

Abstract

Overview

ISO 24509:2019 - Ergonomics - Accessible design - A method for estimating minimum legible font size for people at any age - defines a reproducible, vision‑based method to estimate the minimum legible font size for single characters across a wide range of viewing conditions. It addresses legibility in both self‑luminous and reflected modes for use in documents, product labels, signs and displays where viewing distance, luminance and contrast vary. The method is targeted at people without pathological eye disorders (not for low‑vision populations) and applies primarily to fixed‑size printed materials; applicability to other languages is provided in Annex F.

Key technical topics and requirements

Scope and limits: Applicable for ages 6–90 years, viewing distances 0.2 m–100 m, luminance 0.01–3000 cd/m2 and contrasts 0–100% (Michaelson contrast).
Core inputs: viewer age, viewing distance, luminance, and contrast - identified as the primary vision‑related determinants of single‑character legibility.
Calculation procedure:
- Use normative visual acuity data at 100 cd/m2 (Annex A).
- Apply a luminance correction coefficient (Annex B) to obtain acuity at the actual luminance (Formula (1)).
- Compute a size factor from acuity and viewing distance (Formula (2)).
- Convert the size factor to a minimum legible font size in points using formula Pmin = a + b·S with font‑type coefficients for serif and sans‑serif (Table 1 / Annex G).
- Apply a contrast correction multiplier from Table 2 when contrast

Related standards

Other ISO standards

Overview

Key technical topics and requirements

Scope and limits: Applicable for ages 6–90 years, viewing distances 0.2 m–100 m, luminance 0.01–3000 cd/m2 and contrasts 0–100% (Michaelson contrast).
Core inputs: viewer age, viewing distance, luminance, and contrast - identified as the primary vision‑related determinants of single‑character legibility.
Calculation procedure:
- Use normative visual acuity data at 100 cd/m2 (Annex A).
- Apply a luminance correction coefficient (Annex B) to obtain acuity at the actual luminance (Formula (1)).
- Compute a size factor from acuity and viewing distance (Formula (2)).
- Convert the size factor to a minimum legible font size in points using formula Pmin = a + b·S with font‑type coefficients for serif and sans‑serif (Table 1 / Annex G).
- Apply a contrast correction multiplier from Table 2 when contrast

ISO 24509:2019 PDF

Technical details

Abstract

Overview

Key technical topics and requirements

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Overview

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