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17/03 — 2020
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32.36
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3.2
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<h1>
Font Size Fallacies
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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 class="footnotes" role="doc-endnotes">
<hr />
<ol>
<li id="fn1" role="doc-endnote"><p>https://github.com/nerdypepper/scientifica<a href="#fnref1" class="footnote-back" role="doc-backlink">↩︎</a></p></li>
<li id="fn2" role="doc-endnote"><p>https://en.wikipedia.org/wiki/Dots_per_inch<a href="#fnref2" class="footnote-back" role="doc-backlink">↩︎</a></p></li>
<li id="fn3" role="doc-endnote"><p>https://www.sven.de/dpi/<a href="#fnref3" class="footnote-back" role="doc-backlink">↩︎</a></p></li>
<li id="fn4" role="doc-endnote"><p>https://en.wikipedia.org/wiki/Sony_Xperia_1<a href="#fnref4" class="footnote-back" role="doc-backlink">↩︎</a></p></li>
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<p>I'm Akshay, I go by nerd or nerdypepper on the internet.</p>
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I am a compsci undergrad, Rust programmer and an enthusiastic Vimmer.
I write <a href="https://git.peppe.rs">open-source stuff</a> to pass time.
I also design fonts:
<a href="https://git.peppe.rs/fonts/scientifica">scientifica</a>,
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