Textbook of Usability

The golden ratio (denoted by the Greek letter φ, "phi") is approximately 1.618:1, defined as the proportion where the ratio of the whole to the larger part equals the ratio of the larger part to the smaller:

$$\frac{a+b}{a} = \frac{a}{b} = \varphi \approx 1.618$$

The ratio appears in classical architecture, Renaissance paintings, and many natural forms (nautilus shells, sunflower spirals). It has been claimed to underlie universal human aesthetic preference, though empirical evidence for such a preference is mixed — some studies find a mild preference for golden-ratio rectangles, others find no clear effect or culturally variable preferences.

What is less controversial is that systematic proportion — using a consistent ratio to derive dimensions — produces visual coherence. Whether the ratio is the golden ratio, the square root of 2, a musical interval, or a simple modular grid, consistent application prevents the arbitrary mishmash that makes a design feel uncoordinated.

Applications in design:

• Type scales derived by multiplying/dividing a base size by φ
• Spacing systems (the textbook uses golden-ratio spacing: 0.382, 0.618, 1, 1.618, 2.618 rem)
• Layout proportions for sidebar-to-content ratios
• Image aspect ratios for visual composition

The specific ratio matters less than its consistent application. Any consistent ratio system works; the golden ratio is a convenient and historically resonant choice.