Kerning

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Kerning is the process of adjusting the space between two specific letters to make text look evenly spaced. It matters for readability and visual balance. This is different from tracking, which changes spacing uniformly across a range of characters.

In typography, good kerning makes the gaps between all pairs look about the same. “Keming” is a playful term for bad kerning, like when rn looks like m. The word kern originally comes from metal type, where small pieces overhung the edge of a type piece. Over time kerning referred to shaping those spaces rather than general letter spacing.

With metal type, kerning was hard and expensive, so it was used only for pairs that needed it. When digital fonts arrived, kerning became easy to apply to many pairs. In digital typography, kerning is a number that increases or decreases the space between two letters. The value is given in font units, often 1000 or 2048 units per em. A positive value adds space; a negative value reduces it. Each font can have different kerning values for different pairs.

Most kerning adjustments are negative, bringing certain letters like T, V, W, Y closer to neighboring letters, or fitting punctuation nearby. Positive kerning is used mainly with rare combinations or special characters. Some fonts show many kerning pairs; others use class-based systems to group letters into classes so the same value applies to many pairs.

Not all fonts need kerning. Non-proportional (monospaced) fonts typically don’t kerning because all characters have the same width. OpenType fonts use a sophisticated system (GPOS) to store kerning information efficiently, often with two-dimensional tables that apply a single value to many letter pairs sharing similar shapes. This can also include classes of glyphs to reduce storage.

There are several types of automatic kerning:
- Metric kerning uses the font’s built-in kerning table.
- Optical kerning uses an algorithm to adjust spacing based on how the shapes look, which can be better when mixing fonts.
- Contextual kerning adjusts spacing based on surrounding letters, not just the pair itself (rare in everyday use but important for high-quality typography).

Manual kerning lets a designer override automatic kerning for specific pairs. Some workflows also allow kerning changes without editing the font file, by applying document-level adjustments.

Web and typography tools also support kerning. CSS offers properties such as text-rendering: optimizeLegibility, font-feature-settings, and font-kerning to enable or tweak kerning in browsers. OpenType fonts are generally best for kerning, and many modern systems support their features automatically.

In short, kerning fine-tunes the space between specific letter pairs to improve readability and appearance. When automatic options aren’t ideal, designers can adjust kerning by hand or with external tools to achieve the perfect look.