Fractions

Fractions can be a regularly occurring element in text. They are routinely used in text for measurements and dimensions, recipes, math and science notation, as well as in manuals and other technical documentation. Fractions can be represented in several ways: spelled out, using decimals, by diagonal or slashed fractions, by stacked or nut fractions, or by horizontal fractions. Knowing which form to use and how to locate or create numerical fractions is key to creating the most visually pleasing typography.

The most common typographic treatment (unless otherwise requested) is the diagonal fraction. (Some clients and style manuals may prefer spelled-out fractions in running text, but guidelines for this are often inconsistent, and occasionally even contradictory.) Diagonal fractions can be categorized as prebuilt, automatic, or custom-made.

Prebuilt (also called precomposed) fractions are the most desirable, as they have been individually designed as part of a given typeface. This ensures that their weight, spacing and alignment are uniform and balanced. Additionally, they are built using the actual fraction bar glyph, instead of the slash glyph, which is not intended for this purpose. The best way to view the available prebuilt fractions in a given font is from your software’s glyph panel.

Fractional values can be typeset in several ways: spelled out, as decimals, as stacked or nut fractions, as diagonal or slashed fractions, as well as horizontal.

Unfortunately, prebuilt fractions in most fonts – especially Type 1 and TrueType® font formats – are often limited to the basic (or standard) 1/4, 1/2 and 3/4. An increasing number of OpenType fonts offer a more extensive assortment of prebuilt fractions, including 1/8, 3/8, 5/8, 7/8, and sometimes 1/3 and 2/3, all of which are referred to as extended fractions. But if you need less common or arbitrary fractions (such as 36/297), the prebuilt variety is not an option.

Fractions in typesetting are classified as basic, extended, and arbitrary, as shown in the ITC Galliard® typeface.

Building diagonal fractions on the fly is generally the next best option. Most design software can generate these fractions automatically when you use OpenType® fonts that offer this feature. The software uses numerators and denominators (also known as true-drawn superscript and subscript glyphs), separating them with the fraction bar from the font’s character set. Not all OpenType fonts have this fraction-making capability, but when they do, it is extremely useful for fractions not prebuilt in the font.

If the Fractions feature isn’t available for the font or software in use, you can make fractions manually. If the font includes a full set of true superscript and subscript numerals, use them. If not, full size numerals can be converted using the superscript and subscript option. This method can work in a pinch if you only have a few fractions to make, but your fractions will look lighter in weight than the surrounding text or other characters. Allow time to size, kern, and align the elements carefully, and remember to use the fraction bar rather than the more familiar forward slash.

Stacked fractions (also called nut or case fractions) are occasionally called for in measurements or mathematics, or when space is at a minimum. Unfortunately, they are rarely available prebuilt, and when they are, usually only for a limited number of standard fractions. Most software does not currently offer the ability to create nut fractions on the fly.

Horizontal fractions are harder to read than diagonal fractions, due to their full-sized numerators and denominators. They take up considerably more space and are rather clumsy in appearance. They should be considered a last resort rather than a first choice.

The best way to approach the issue of setting fractions is to determine at the outset of a project whether they will be required. Certain fonts can reduce, or even eliminate, the need to build a large quantity of fractions, either automatically or manually. If possible, select fonts and software that will allow you to set pleasing, consistent fractions that will not disrupt the harmony of the text.

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Editor’s Note:Ilene Strizver, founder of The Type Studio, is a typographic consultant, designer and writer specializing in all aspects of typographic communication. She conducts Gourmet Typography workshops internationally. Read more about typography in her latest literary effort, Type Rules! The designer's guide to professional typography, 4th edition, published by Wiley & Sons, Inc. This article was commissioned and approved by Monotype Imaging Inc.