Is a 1500 upm ok?

ok_locksmith_8414 · July 10

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?

Thomas Phinney · July 10

Yes

For most purposes, that is absolutely fine. You can use any em value between, roughly 700 and 2500 and everything is fine. Maybe even 3000 or so.

There are a few players who might care (e.g. Microsoft) so different rules apply if you are making a font specifically for them. But generally, it is a non-issue in the real world today.

John Hudson · July 10

Back in 2008, when work first began on the Brill types, there was a known issue with some third party PDF tools and viewers incorrectly assuming that all CFF-flavour OpenType fonts would have a 1000 UPM, resulting in incorrect scaling and/or linespacing. That no longer seems to be an issue, so for v5.00 we scaled everything up to a 4000 UPM to enable easier handling of fine details.

Matthew Smith · July 10

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 · July 10

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.

Igor Petrovic · July 12

I follow 1000UPM wherever it is possible, because all reference numbers in a font (overshoot, stem thickness in thin and black master, etc.) are usually presented at that resolution (in my head and in other typefaces).

For example, I know that the lowercase vertical stem in the black master is usually somewhere around 200 units. In thin ~25 units. And gives me a general direction I like to have.

If a font requires more detailed resolution because of its design, then I go to 2000UPM because it is easier for me to count reference numbers that way. Also, it is usually quite sufficient in a technical sense.

Johannes Neumeier · July 14

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 · 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.

Aaron Muir Hamilton · August 21

I like 1 980 UPM, since it is the product of 2⁲ × 3⁲ × 5 × 11, it divides by 3, 4, 5, 6, 9, 11, and 15; these e.g. respectively:

three-per-em space
four-per-em space ― and therefore the en space and 1⁄2 em tabular figures.
six-per-em space
the thin space ― usually 1⁄5 em.
the medium mathematical space ― 2⁄9 em for some reason.
a common narrow punctuation width of 1⁄11 em ― shared between U+2008 Punctuation Space, period, comma, colon, semicolon, and interpunct... at least when tabular figures are enabled. If you don't like 1⁄11 em punctuation, 1 980 is also divisible by 12 and 10.
1⁄15 for hair spaces at exactly 1⁄3 of the thin space (another common definition is one 16ᵗʰ, but that would require a much bigger base somewhere north of 7000 units).

It also has very small residues when dividing by 7 or 8, and it looks cool in binary.

Is a 1500 upm ok?

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