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Briem’s notes on type design: Font metrics can help you

Groups and pairs

A font metrics file, sometimes called AFM, comes with many fonts. It is a text document. Any word processor can open it. At first glance it may look confusing, but it’s worth a look. A font metric file has useful information.

To begin with, you’ll find the width of every character. It also has a list of kerning pairs. Both can be useful to you.

Kerning pairs

Some letter combinations can look awkward in a well-spaced typeface. The letters H and e may look just right. But the letters W and e can look too far apart. That’s when you need exceptions from usual character width.

Some typefaces have a dozen or two kerning pairs. Others use hundreds. You may like to see how other people arrange their handiwork. Each font of the BriemOperina family has 88. Here are the first five.

StartKernPairs 88
KPX A T -20
KPX A V -30
KPX A Y -40
KPX A quoteright -60
KPX F comma -40

The letters KPX at the beginning of each line tell you that you’re looking at kerning pairs. The numbers at the end (-20, -30, etc) are kerning values, and won’t be of much practical use to you. But between the KPX and the numbers is useful information.


These are kern pairs: character combinations that usually look awkward unless you give them a helping hand. When you want to edit your own kern pairs, a list of likely troublespots can save you a great deal of effort.

Width groups

The AFM information about the four letters X Y Z and the bracket character looks like this.

C 88 ; WX 343 ; N X ; B 0 0 343 410 ;
C 89 ; WX 311 ; N Y ; B 0 0 311 410 ;
C 90 ; WX 326 ; N Z ; B 0 0 326 410 ;
C 91 ; WX 217 ; N bracketleft ; B 0 -162 185 478 ;

The first part, C 88, is the ascii number. The second, WX 343, is the width. The third, N X, is the name.

When is a width table useful to you? Let me give you an example. When your type is used for tables, you want some of your characters to have the same width as the numerals. Otherswise, the columns won’t be straight. A narrow equal sign can cause a lot of unnecessary trouble.

How to find width groups

I suggest you use a spreadsheet. First, use search-and-replace to substitute the ” ; ” (wordspace, semicolon, wordspace) by the TAB character. Then copy and paste what you want to sort into a spreadsheet. The width will land in the second column.

Sort the spreadsheet data by the values of the second column. The characters that belong together will form clusters. You can expect these on your list.

N numbersign
N less
N equal
N greater
N cent
N sterling
N yen
N florin
N currency

Some designs have these as well.

N underscore
N section
N endash
N dagger
N daggerdbl

You should also look for characters that are half the width of numerals, such as the period and the comma.

A word of warning

By coincidence, a few characters may have the same width as numerals. If you find the letter w among them, for example, toss it out.

When in doubt, use your eyes. Common sense also helps.

Notes on type design. Copyright © 1998, 2001, 2022 Gunnlaugur SE Briem. All rights reserved. Republished with permission in 2022 by Fontlab Ltd.