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17/03 — 2020
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32.37
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3.3
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<h1>
Font Size Fallacies
</h1>
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<p>I am not an expert with fonts, but I do have some experience <a
href="#fn1" class="footnote-ref" id="fnref1"
role="doc-noteref"><sup>1</sup></a>, and common sense. This post aims to
debunk some misconceptions about font sizes!</p>
<p>11 px on your display is <em>probably not</em> 11 px on my display.
Let’s do some quick math. I have two displays, 1366x768 @ 21” and
another with 1920x1080 @ 13”, call them <code>A</code> and
<code>B</code> for now.</p>
<p>Display <code>A</code> has 1,049,088 pixels. A pixel is a square, of
side say, <code>s</code> cm. The total area covered by my 21” display is
about 1,066 cm^2 (41x26). Thus,</p>
<pre><code>Display A
Dimensions: 1366x768 @ 21" (41x26 sq. cm)
1,049,088 s^2 = 1066
s = 0.0318 cm (side of a pixel on Display A)</code></pre>
<p>Bear with me, as I repeat the number crunching for Display
<code>B</code>:</p>
<pre><code>Display B
Dimensions: 1920x1080 @ 13" (29.5x16.5 sq. cm)
2,073,600 s^2 = 486.75
s = 0.0153 cm (side of a pixel on Display B)</code></pre>
<p>The width of a pixel on Display <code>A</code> is <em>double</em> the
width of a pixel on Display <code>B</code>. The area occupied by a pixel
on Display <code>A</code> is <em>4 times</em> the area occupied by a
pixel on Display <code>B</code>.</p>
<p><em>The size of a pixel varies from display to display!</em></p>
<p>A 5x11 bitmap font on Display <code>A</code> would be around 4 mm
tall whereas the same bitmap font on Display <code>B</code> would be
around 1.9 mm tall. A 11 px tall character on <code>B</code> is visually
equivalent to a 5 px character on <code>A</code>. When you view a
screenshot of Display <code>A</code> on Display <code>B</code>, the
contents are shrunk down by a factor of 2!</p>
<p>So screen resolution is not enough, how else do we measure size?
Pixel Density! Keen readers will realize that the 5^th grade math
problem we solved up there showcases pixel density, or, pixels per cm
(PPCM). Usually we deal with pixels per inch (PPI).</p>
<p><strong>Note:</strong> PPI is not to be confused with DPI <a
href="#fn2" class="footnote-ref" id="fnref2"
role="doc-noteref"><sup>2</sup></a> (dots per inch). DPI is defined for
printers.</p>
<p>In our example, <code>A</code> is a 75 ppi display and <code>B</code>
is around 165 ppi <a href="#fn3" class="footnote-ref" id="fnref3"
role="doc-noteref"><sup>3</sup></a>. A low ppi display appears to be
‘pixelated’, because the pixels are more prominent, much like Display
<code>A</code>. A higher ppi usually means you can view larger images
and render crispier fonts. The average desktop display can stuff 100-200
pixels per inch. Smart phones usually fall into the 400-600 ppi
(XXXHDPI) category. The human eye fails to differentiate detail past 300
ppi.</p>
<p><em>So … streaming an 8K video on a 60” TV provides the same clarity
as a HD video on a smart phone?</em></p>
<p>Absolutely. Well, clarity is subjective, but the amount of detail you
can discern on mobile displays has always been limited. Salty consumers
of the Xperia 1 <a href="#fn4" class="footnote-ref" id="fnref4"
role="doc-noteref"><sup>4</sup></a> will say otherwise.</p>
<p>Maybe I will talk about font rendering in another post, but thats all
for now. Don’t judge a font size by its screenshot.</p>
<section id="footnotes" class="footnotes footnotes-end-of-document"
role="doc-endnotes">
<hr />
<ol>
<li id="fn1"><p>https://github.com/nerdypepper/scientifica<a
href="#fnref1" class="footnote-back" role="doc-backlink">↩︎</a></p></li>
<li id="fn2"><p>https://en.wikipedia.org/wiki/Dots_per_inch<a
href="#fnref2" class="footnote-back" role="doc-backlink">↩︎</a></p></li>
<li id="fn3"><p>https://www.sven.de/dpi/<a href="#fnref3"
class="footnote-back" role="doc-backlink">↩︎</a></p></li>
<li id="fn4"><p>https://en.wikipedia.org/wiki/Sony_Xperia_1<a
href="#fnref4" class="footnote-back" role="doc-backlink">↩︎</a></p></li>
</ol>
</section>
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<div class="intro">
Hi.
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<p>I'm Akshay, programmer and pixel-artist.
I write <a href="https://git.peppe.rs">open-source stuff</a>.
I also design fonts:
<a href="https://git.peppe.rs/fonts/scientifica/about">scientifica</a>,
<a href="https://git.peppe.rs/fonts/curie/about">curie</a>.
</p>
<p>Reach out at [email protected].</p>
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