Is a 1500 upm ok?

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Ok so long story short, I’ve posted here before about a typeface I’m designing. The typeface has a units per em value of 1500. I know some of you might say that the most common values are 1000 and 2048.

When I first started working on this project, I was still very new to using Glyphs App and thought that changing the units per em was a way to scale the glyphs up which is what I wanted to do at the time. That was about 1 year ago, and I hadn’t really thought about it again until recently, when I heard that typefaces can run into issues in some environments if they don’t use 1000 or 2048 units per em.

However, I hear with modern technology, using values other than 1000 or 2048 isn’t necessarily a problem. The good news is that my typeface interpolates wonderfully at 1500, and the sizing looks fine when I test it alongside other fonts like Inter and Helvetica.

I really don’t want to go through the hassle of scaling everything down, fixing errors, and learning new metrics. Should I just leave it at 1500 and hope for the best?

Best Answers

Answers

  • I can’t speak to the technical limitations of how high you can go, but if it means anything to you, Sharp Type’s Carta Nueva has a UPM of 4096.
  • Thomas Phinney
    Thomas Phinney Posts: 3,037
    There have been some historical issues, one of which John mentions. But as far as I know, they have been long since resolved.

    Google’s icon fonts have a non-standard em square, as well. Material Symbols have a 960-unit em square (with TrueType outlines, not CFF), and their predecessor Material Icons had a 480-unit em. I did end up doubling the em square when developing Material Symbols (which started in 2020), but only late in the game, and purely for design reasons — not because of bug reports with either the new font or its predecessor.
  • Nowadays any UPM value is technically fine. Note that fonts with higher UPM value have marginally bigger file sizes. It hardly matters, even in a web context, but it's worth noting. It's easy enough to compare the difference with a quick export from your font editor.
  • Thomas Phinney
    Thomas Phinney Posts: 3,037
    edited July 14
    Well, not any UPM value! Maybe Johannes means “any arbitrary value within certain limits).

    For a maximum, there are both format limitations and implementation-support limitations.

    But as long as all glyph and metadata coordinates are within +/- 4096, you are unlikely to trip over any such limit.