LEGIBILITY AND READABILITY

Legibility and readability are fundamental to successful typographic design. Often the terms are used interchangeably. Yet, there is a difference between them.

LEGIBILITY
Legibility is concerned with how easy it is to distinguish individual letters. The simpler a type design is, the more legible it is. So why do less-than-legible typefaces even exist? Because typeface designers love to create unique and distinctive designs, of course. While it is generally better to always choose a legible type, there are times when distinctiveness may be more important than legibility. For example, when selecting a font for a unique and distinctive company logo.

There are three design features that make a typeface legible:

1. Large X-Height:
A large x-height increases the negative space within each letter. This makes it’s shape much more discernable.

2. Large Counters:
The negative space within a letter is called a counter. When a typeface has large counters, it is easier to distinguish the shape of each individual letter.

3. Simple Letterforms:
The simpler a letterform, the more legible it is. Sans serif types are generally more legible than their serif counterparts because they do not have any serifs interfering with the shapes of the letters. However, this does not mean that sans serifs are necessarily easier to READ in text. Actually, serif types are generally considered MORE readable. The exception to this rule is on-screen. Because of on-screen distortion, sans serif is the best choice for readability.

Some common typefaces which meet these three criteria are: Helvetica, Novarese, New Century Schoolbook, Cheltenham, Times Roman, Gill Sans, and Baskerville.

Here are some examples of fonts which may be fun, but are not very legible:

READABILITY
Readability refers to the ease with which a reader can scan over paragraphs of type. In other words, how easy it is to read! While legibility is basically dependent on the typeface design, readability is dependent on the manipulation or handling of the type. A highly legible typeface can be made unreadable by poor typographic design. Factors which affect readability include: line lengths, point size, leading, typeface selection, spacing, type alignment, and background.

RULE ONE - AVOID CAPITALS
Ninety-five percent of what we read is in lowercase letters. Not only are we much more used to reading them, but they also assist us because they create a recognizable shape (coastline). Words in capital letters have no distinctive shape (or coastline).

One of the most unreadable combinations is using capital letters and a typeface with reduced legibility. Using a script typeface in capital letters is definitely a big no-no:

And don't forget about the use of uppercase in email communication. Very bad etiquette! All caps in email means you are SHOUTING at someone, so don't do it!

RULE TWO: USE A REASONABLE POINT SIZE
Use a size suitable for your audience. Ideal text type size ranges from 9-12 point depending on the x-height. Remember older people may need a larger point size to read.

RULE THREE: DON’T USE A LINE LENGTH TOO SHORT OR TOO LONG
Very short or long lines disrupt the reader’s rhythm, making it harder to read. Very short lines run the risk of creating rivers if justified alignments used. If long lines are unavoidable, extra leading can help offset the problem.

Very long lines disrupt reading. When the eyes get tired, they are no longer able to find the beginning of the next line of type. An ideal line length can be estimated by doubling the point size. For instance, 12 point type should have a line length of 24 picas (or four inches). Generally, shorter lines should be used for typefaces with small x-heights and thick/thin designs, and also bold and italic fonts. Usually a serif typeface can tolerate a longer line than a sans serif.

RULE FOUR: CREATE EVEN WORD SPACING
If word spaces are too large, they break the lines up into separate elements and disrupt reading. This is especially true if justified type is used on a short line length. If the word spaces are too small, it becomes difficult to distinguish each separate word. A good trick to use to check word spacing is to turn the page upside down and squint at it. Excessively large word spaces will stand out. Be especially careful with condensed and expanded fonts, reversed type, and vertical, narrow typefaces (like Bodoni).

RULE FIVE: CREATE EVEN LETTER SPACING
When letters are correctly spaced, a paragraph of type takes on an even color. From a distance it should look like a screened gray block. The shade of gray will depend on the heaviness of the typeface. Any interference with normal letter spacing is very hard to read. If the letter spacing is uneven, darker spots stand out in places against the gray color. Often, tight tracking will create uneven letter spacing.

RULE SIX: THINK ABOUT THE BACKGROUND
An important factor in the readability of type is the background on which it is placed. This includes not only any printed blocks of color, screens or black backgrounds, but also the kind of paper the type appears on. When selecting a typeface, think carefully about what kind of background it will be placed on. For instance, a fine, light typeface will not stand out well on black or screened background, or on textured/glossy paper. To avoid readability problems, never place text type on black or screened backgrounds. It’s too hard to read!

A strong sans serif headline, however, is a good choice for a black or screen background:

RULE SEVEN:PROVIDE AMPLE LEADING (LINE SPACING)
Line spacing has an important function in readability; it acts as a guideline to the next line. If the leading is too tight, these guidelines are lost and readers are more likely to skip lines. In addition, the type looks dark and uninviting which makes reading more difficult. When the leading is too wide, it begins to compete with the type for the reader’s attention.

There are no firm rules for determening ideal leading. Many factors need to be considered including: x-height, weight of type, point size, case, line length, etc. Also keep in mind the function of the design. Text for prolonged reading should have wider leading, but when only a small piece of information needs to be read (e.g. directory), leading can be tighter.

As a general guideline, the ideal line space is considered to be 120% of the point size. For example, 10 point type would be set with 12 point leading. A page-layout program’s auto leading option is also 120% of the point size. Negative leading (when the point size is greater than the leading) should only be considered when using all uppercase letters, or lowercase letters without descenders.

Here are some general guidelines for selecting the right leading:

RULE EIGHT: SELECT THE MOST READABLE TYPE ALIGNMENT
As a general rule, the most readable type alignments are justified and flush left. The reason for this is that they both provide a straight left margin for the reader to return to. Centered and flush right alignments are ragged on the left and therefore much harder to read in large quantities.

However, justified and flush left alignments also have their readability problems. Although justified type is the preferred alignment for most books, magazines and newspapers, it can have bad word spacing problems if the type is set on too short a line length. Flush left, on the other hand, usually has even word spacing. Sometimes, though, a very ragged right edge can create readability problems too.

Another definition of Typography: