행의 길이 (Measure)

Measure is the length of a line of text — the horizontal distance from the left edge to the right edge of a text block. It is one of the most consequential decisions in typography because line length directly controls readability: if lines are too short, the eye interrupts its rhythm too frequently; if lines are too long, the eye struggles to locate the beginning of the next line.

The typographic consensus, backed by decades of readability research, is that optimal measure for running text falls between 45 and 75 characters per line, including spaces. The sweet spot is often cited around 66 characters. For narrow columns, 45 characters is a reasonable minimum. Beyond 85–90 characters, reading comprehension and eye tracking begin to degrade measurably.

/* The ch unit is ideal for controlling measure */
/* 1ch = the width of the '0' character in the current font */
.article-body {
  max-width: 65ch;
  /* Approximately 65 characters per line — within optimal range */
}

/* More conservative approach for complex or dense content */
.complex-content {
  max-width: 55ch;
}

/* Shorter measure for UI text and card content */
.card-description {
  max-width: 45ch;
}

/* Multiple columns can maintain measure even in wide containers */
.wide-article {
  columns: 2;
  column-gap: 3rem;
  max-width: 130ch; /* 2 columns × 65ch + gap */
}

/* Responsive measure that scales appropriately */
.responsive-text {
  width: min(65ch, 100% - 2rem);
  margin-inline: auto;
}

The ch unit in CSS is specifically designed for this purpose — one ch equals the width of the '0' character in the current font and size. It provides a typographically meaningful measurement unit. However, since character widths vary significantly between typefaces (a condensed sans-serif has much narrower characters than a wide display face), ch measurements are approximate guides rather than precise character counts. Testing with real content is always necessary.

Measure interacts directly with leading. When lines are long, the eye needs more vertical space (larger line-height) to easily find the beginning of the next line. Short-measure columns (newspaper columns, sidebars) can tolerate tighter leading because the eye has a short return trip. This relationship means that measure adjustments often require corresponding line-height adjustments.

Typefaces like Merriweather and Lora are specifically designed for comfortable long-form reading — their metrics work best within the 55–70ch range where their stroke contrast and x-height create maximum legibility.