Webapp > Help > Text size understanding : comments on pt => px conversion

[ArnaudDelafosse]

Observed behaviour

In the "Help" > "Minimum ratio" > " Level AA" and "Text size understanding" sections, it is implied that 14pt is equivalent to 14px and that 18pt is equivalent to 18px.

Expected behaviour

I believe this is incorrect if you follow the W3C's own "Contrast (Minimum) Understanding SC 1.4.3" in the "Note 1" section where it says "The ratio between sizes in points and CSS pixels is 1pt = 1.333px, therefore 14pt and 18pt are equivalent to approximately 18.5px and 24px."

What I understand is that for a given standard font-size where body { font-size: 100%; } p { font-size: 1rem; } sets your paragraphs a font-size of (equivalent to) 16px, contrast ratios for level AA should be at least:

• 4,5 for body copy,
• 3 for text in bold with a font-size of at least (equivalent to) 18.5px or 120% of body copy,
• 3 for large text with a font-size of at least (equivalent to) 24px or 150% of body copy.

/!\ Reminder: do not use px to set your font sizes, these are pixel equivalences. Always use relative units like rem, em or %.

Steps to reproduce the behaviour

See this example on CodePen: https://codepen.io/ArnzWeb/full/WMdmGB/ (it's in French and I've voluntarily rounded 18.5 to 19px).

[mfaure]

Thanks @ArnaudDelafosse for your clever feedback! This note wasn't present at the time of the doc writing. I just grep'd some git logs and found it was introduced on May 23, 2016.

Would you feel comfortable with fixing the doc ?

[ArnaudDelafosse]

You're welcome, glad to bring a bit of help to this great tool.
Yes I'm fine with amending the doc, I'll try as soon as I can.

[dzc34]

files impacted:

• documentation/en/Howto-use.md ---> PR DOC - Howto-use.md / Update for the pt => px conversion section #143
• webapp (HTML in i18n file)
  • English i18n file
  • French i18n file
  • Korean i18n file

[ArnaudDelafosse]

Once the suggestions I made for the Howto page are validated or not, I'll mirror that on the 2 remaining files.

[dzc34]

Thanks @ArnaudDelafosse for your contributing!
I splited your merge request #140 in two part for more easy review:

• DOC - Howto-use.md improvements ( syntax corrections, match titles to application labels) #142 - DOC - Howto-use.md improvements (syntax corrections, match titles to application labels)
• DOC - Howto-use.md / Update for the pt => px conversion section #143 - DOC - Howto-use.md / Update for the pt => px conversion section

#142 is now merged in develop branch.

[dzc34]

other resources:

• w3c/wcag - "Large text" - using px rather than pt as unit
• DISIC/rgaa_referentiel - Meilleure indication de la taille de caractères pour le calcul des contrastes