Scale (ratio)

Common forms of scale

• Representative fraction (RF): a simple ratio like 1:25 or 1:250,000.
• Verbal scale: a sentence such as "one centimetre represents one kilometre." This makes units explicit.
• Graphic (bar) scale: a drawn line or bar subdivided to show ground distances; it remains useful when a reproduction changes size.

Practical examples

For a 1:50,000 topographic map, 1 cm equals 50,000 cm (that is, 500 m). A model produced at 1:25 scale of a 30 m tall building will be 30 m ÷ 25 = 1.2 m tall. Scales apply equally to photographs: a large-format aerial photograph may have a detailed scale while a general view has a smaller (more reduced) scale; see photograph.

Effects on area and volume

Linear scale factors extend non-linearly to area and volume. If the linear scale is 1:n, areas are reduced by 1:n^2 and volumes by 1:n^3. For example, a surface 1,000 m^2 at 1:100 scale appears as 0.1 m^2 in a plan.

History, conventions and best practices

Cartographers and designers choose scales to balance coverage and detail: "large-scale" maps show small areas with more detail, while "small-scale" maps cover large areas with less detail. Always check the scale format and units, use a graphic scale when possible to guard against resizing, and remember that projection and generalization can affect how accurately distances and areas are represented.

Other uses include architectural drawings, scale models and technical illustrations. When working with a drawing, a physical model or a measurement exercise, explicitly state the scale and unit conversions to avoid errors. For more resources on interpreting scales and measurements see examples and guides.