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MAKE IT BIG
The Effect of Font Size and Line Spacing on Online Readability.
Luz Rello Martin Pielot Mari-Carmen Marcos
CHI...
Online Reading is a daily habit for many
WHICH FONT SIZE FOR BEST READABILITY?
readability refers to the ease with
which a reader can read and
understand a written text. It only
refers to the propertie...
16 pixels 12 points
PIXELS AND POINTS
• Points (pts)
– resolution-independent unit
– 72 pts = 1 inch = 2.54 cm
• Pixels (px)
– used to be reso...
PREVIOUS SCIENTIFIC STUDIES
Authors Year Method Tested Sizes Best Size
Bernard et al. 2001,
2002,
2003
read-aloud 10-14 pt...
• Confusing, conflicting, and evidence-
lacking advice in forums
• Scientific research found „bigger is
better“ but we did...
IN THIS PAPER
• control group (n=104) of study to determine
optimal font size for people with dyslexia
• much larger font ...
methodology
STUDY SETUP
• screen : 17 inch TFT, 1024x768
• eye tracker : tobii 1750
• website : wikipedia (animals)
• browser : firefo...
INDEPENDENT MEASURES
• font size (pt) : 10, 12, 14, 18, 22, 26
within-subject factor
• line spacing : 0.8, 1.0, 1.4, 1.8
b...
Dependent Measures
MEAN FIXATION DURATION
as objective measure for readability
COMPREHENSION QUESTIONS
to avoid that participants just „skim“ the text
SUBJECTIVE READABILITY & COMPREHENSION
to identify mismatch between perceived and objective performance
reading
PARTICIPANTS
• 104 volunteers (61 female, 43 male)
• 92 studying or had finished university
• aged 14* – 54 (M = 30.24, SD...
results
Font Size
10 12 14 18 22 26
0.100.200.300.40
Font Size
FixationDurationMean(ms)
0.8 1
0.100.200.300.40
Line Sp
FixationDurationMean(...
sig. effect of font size
F(5,445) = 5.2489, p < .001
small effect size
(η2 = 0.025)
pairwise comparison
• 10pt <12pt
MEAN ...
sig. effect of font size
χ2 (5) = 135.85, p < .001
pairwise comparison
• 10pt < than all larger
• 12pt < than all larger
•...
sig. effect of font size
χ2 (5) = 27.29, p < .001
sig. less correct answers for
• 10 & 12 compared to 18 pt
• 12 pt compar...
sig. effect of font size
F (5, 363) = 18.614, p < .001
pairwise comparison
• 10pt < 14pt +
• 12pt < 14pt +
SUBJECTIVE COMP...
Line Spacing
0.8 1 1.4 1.8
0.100.200.300.40
Line Spacing
FixationDurationMean(ms)FixationDurationMean(s)
Line Spacing
no sig. effect of...
no sig. effect of font size
F (3, 365) = 2.074, p = .103
SUBJECTIVE READABILITY
no evidence re: line spacing
0%!
20%!
40%...
sig. interaction effect between
font size x line spacing
F (15, 445) = 4.098, p < .001)
small effect size
(η2 = 0.034)
no ...
sig. effect of line spacing
χ2 (3) = 19.56, p < .001
sig. less correct answers for
• 0.8 compared to all other
line spacin...
sig. effect of line spacing
F (3, 365) = 3.249, p = .022
pairwise comparison
• 1.0 > 1.8
SUBJECTIVE COMPREHENSION
 subj. ...
conclusions
USE 18 POINT FONT SIZE
• 18 pts and larger had best objective readability
• subjective readability was highest for 18 pts
...
STARK CONTRAST TO COMMON
RECOMMENDATIONS
Set Chrome or Firefox to 24 (pixels)
to have 18 points font size
MAKE IT BIG
The Effect of Font Size and Line Spacing on Online Readability.
CHI 2016: ACM Conference on Human Factors in C...
Make it Big! The Effect of Font Size and Line Spacing on Online Readability.
Make it Big! The Effect of Font Size and Line Spacing on Online Readability.
Make it Big! The Effect of Font Size and Line Spacing on Online Readability.
Make it Big! The Effect of Font Size and Line Spacing on Online Readability.
Make it Big! The Effect of Font Size and Line Spacing on Online Readability.
Make it Big! The Effect of Font Size and Line Spacing on Online Readability.
Make it Big! The Effect of Font Size and Line Spacing on Online Readability.
Make it Big! The Effect of Font Size and Line Spacing on Online Readability.
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Make it Big! The Effect of Font Size and Line Spacing on Online Readability.

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Experiment highlighting the drastic effect of font size and line spacing on readability.
* readability improved significantly until 18 points
* comprehension was impaired for 10 and 12 points
* line spacing has little effect, but extreme deviations from default may impair comprehension
Presented at ACM CHI 2016: the top conference for Human-Computer Interaction.

Published in: Science
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Make it Big! The Effect of Font Size and Line Spacing on Online Readability.

  1. 1. MAKE IT BIG The Effect of Font Size and Line Spacing on Online Readability. Luz Rello Martin Pielot Mari-Carmen Marcos CHI 2016: ACM Conference on Human Factors in Computing Systems San Jose McEnery Convention Center, May 7 – 12 at San Jose, CA, USA Presenter: Martin Pielot, @martinpielot
  2. 2. Online Reading is a daily habit for many
  3. 3. WHICH FONT SIZE FOR BEST READABILITY?
  4. 4. readability refers to the ease with which a reader can read and understand a written text. It only refers to the properties of the presentation of the text, not the content of the text itself
  5. 5. 16 pixels 12 points
  6. 6. PIXELS AND POINTS • Points (pts) – resolution-independent unit – 72 pts = 1 inch = 2.54 cm • Pixels (px) – used to be resolution dependent – nowadays ¾ of 1 point 16 px = 12pt (*) * https://developers.google.com/speed/docs/insights/UseLegibleFontSizes
  7. 7. PREVIOUS SCIENTIFIC STUDIES Authors Year Method Tested Sizes Best Size Bernard et al. 2001, 2002, 2003 read-aloud 10-14 pts 14 Banerjee et al. 2011 read-aloud 10-14 pts 14 Bhatia et al. 2011 preference 10-14 pts - Beymer & Russel 2005, 2007, 2008 eye-tracker 10-14 pts 14
  8. 8. • Confusing, conflicting, and evidence- lacking advice in forums • Scientific research found „bigger is better“ but we did not find any test with fonts larger than 14 points.
  9. 9. IN THIS PAPER • control group (n=104) of study to determine optimal font size for people with dyslexia • much larger font sizes (up to 26 points) results challenge existing insights and recommendations
  10. 10. methodology
  11. 11. STUDY SETUP • screen : 17 inch TFT, 1024x768 • eye tracker : tobii 1750 • website : wikipedia (animals) • browser : firefox • font : arial
  12. 12. INDEPENDENT MEASURES • font size (pt) : 10, 12, 14, 18, 22, 26 within-subject factor • line spacing : 0.8, 1.0, 1.4, 1.8 between-group factor
  13. 13. Dependent Measures
  14. 14. MEAN FIXATION DURATION as objective measure for readability
  15. 15. COMPREHENSION QUESTIONS to avoid that participants just „skim“ the text
  16. 16. SUBJECTIVE READABILITY & COMPREHENSION to identify mismatch between perceived and objective performance reading
  17. 17. PARTICIPANTS • 104 volunteers (61 female, 43 male) • 92 studying or had finished university • aged 14* – 54 (M = 30.24, SD = 9.13) • normal or corrected-to-normal vision * Minors were accompanied by parents
  18. 18. results
  19. 19. Font Size
  20. 20. 10 12 14 18 22 26 0.100.200.300.40 Font Size FixationDurationMean(ms) 0.8 1 0.100.200.300.40 Line Sp FixationDurationMean(ms) FixationDurationMean(s) FixationDurationMean(s) Font Size Line Sp sig. effect of font size F(5,445) = 66.825,p < .001 large effect size (η2 = 0.159) pairwise comparison • 10pt > than all larger • 12pt > than all larger • 14pt > than all larger • 18pt > than 22pt MEAN FIXATION DURATION objective readability best for 18/22/26 pts
  21. 21. sig. effect of font size F(5,445) = 5.2489, p < .001 small effect size (η2 = 0.025) pairwise comparison • 10pt <12pt MEAN NUMBER OF FIXATIONS limited effect on number of fixations 10 12 14 18 22 26 0100200300400500600 Font Size FixN
  22. 22. sig. effect of font size χ2 (5) = 135.85, p < .001 pairwise comparison • 10pt < than all larger • 12pt < than all larger • 14pt < than 18pt • 26pt < than 18pt SUBJECTIVE READABILITY best subjective readability for 18 pt font size 0%! 20%! 40%! 60%! 80%! 100%! 10! 12! 14! 18! 22! 26! ReadabilityRating! Font Size! very good! good! neutral! bad! very bad!
  23. 23. sig. effect of font size χ2 (5) = 27.29, p < .001 sig. less correct answers for • 10 & 12 compared to 18 pt • 12 pt compared to 26 pt COMPREHENSION SCORES small fonts may impair comprehension 0%! 20%! 40%! 60%! 80%! 100%! 10! 12! 14! 18! 22! 26! CorrectResponses! Font Size! Wrong! Correct!
  24. 24. sig. effect of font size F (5, 363) = 18.614, p < .001 pairwise comparison • 10pt < 14pt + • 12pt < 14pt + SUBJECTIVE COMPREHENSION  subjective comprehension impaired for 10 & 12 pt 0%! 20%! 40%! 60%! 80%! 100%! 10! 12! 14! 18! 22! 26! ComprehensionRating! Font Size! very good! good! neutral! bad! very bad!
  25. 25. Line Spacing
  26. 26. 0.8 1 1.4 1.8 0.100.200.300.40 Line Spacing FixationDurationMean(ms)FixationDurationMean(s) Line Spacing no sig. effect of line spacing F (3, 89) = 0.064, p = .978 MEAN FIXATION DURATION no evidence re: line spacing
  27. 27. no sig. effect of font size F (3, 365) = 2.074, p = .103 SUBJECTIVE READABILITY no evidence re: line spacing 0%! 20%! 40%! 60%! 80%! 100%! 10! 12! 14! 18! 22! 26! ReadabilityRating! Font Size! very good! good! neutral! bad! very bad! 0%! 20%! 40%! 60%! 80%! 100%! 0.8! 1! 1.4! 1.8! ReadabilityRating! Line Spacing! very good! good! neutral! bad! very bad!
  28. 28. sig. interaction effect between font size x line spacing F (15, 445) = 4.098, p < .001) small effect size (η2 = 0.034) no interact. effect for 10-18 pt marginal effect for 10-22 pt MEAN FIXATION DURATION  larger fonts are affected by line spacing 0.000.100.200.30 Fontsize FixationDuration(mean) 10 12 14 18 22 26 ● ● ● ● ● ● ● ● ● ● ● ● ● ● 1.4 1.8 0.8 1
  29. 29. sig. effect of line spacing χ2 (3) = 19.56, p < .001 sig. less correct answers for • 0.8 compared to all other line spacings COMPREHENSION SCORES  small line spacings may impair comprehension 0%! 20%! 40%! 60%! 80%! 100%! 0.8! 1! 1.4! 1.8! CorrectResponses! Line Spacing! Wrong! Correct!
  30. 30. sig. effect of line spacing F (3, 365) = 3.249, p = .022 pairwise comparison • 1.0 > 1.8 SUBJECTIVE COMPREHENSION  subj. comprehension impaired for largest spacing 0%! 20%! 40%! 60%! 80%! 100%! 0.8! 1! 1.4! 1.8! ComprehensionRating! Line Spacing! very good! good! neutral! bad! very bad!
  31. 31. conclusions
  32. 32. USE 18 POINT FONT SIZE • 18 pts and larger had best objective readability • subjective readability was highest for 18 pts USE 1.0 or 1.4 LINE SPACING • comprehension scores were lower for 0.8 • subjective comprehension was affected for 1.8 AVOID 10 AND 12 POINT FONT SIZE • comprehension scores were lowest • readability (subj + obj) was worst
  33. 33. STARK CONTRAST TO COMMON RECOMMENDATIONS
  34. 34. Set Chrome or Firefox to 24 (pixels) to have 18 points font size
  35. 35. MAKE IT BIG The Effect of Font Size and Line Spacing on Online Readability. CHI 2016: ACM Conference on Human Factors in Computing Systems San Jose McEnery Convention Center, May 7 – 12 at San Jose, CA, USA 18 POINT FONT SIZE (24 px) default OR slightly larger LINE SPACING 10 AND 12 PTS IMPAIRED UNDERSTANDING Presenter: Martin Pielot, @martinpielot Luz Rello Martin Pielot Mari-Carmen Marcos

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