A metric scale is a measuring tool used in technical drawing that works with the International System of Units (SI) and is based entirely on decimal relationships. Unlike engineer’s or architect’s scales, which often use feet, inches, or fractions, a metric scale relies on units like millimeters and meters and scales such as 1:20, 1:25, 1:50, 1:100, and so on.
When using a metric scale, a ratio like 1:20 means that 1 unit on the drawing equals 20 units in real life. The unit itself—whether millimeters or meters—depends on the context of the drawing. In architectural and engineering drawings, the most common base unit is the millimeter, which simplifies measurement because there’s no need to convert between millimeters and centimeters or meters during layout or fabrication.
For example, at 1:50 scale, a wall that measures 100 millimeters on the drawing represents a real-world length of 5,000 millimeters, or 5 meters. The math is always straightforward: multiply the drawing dimension by the scale factor. If you’re working at 1:25, then 40 mm on paper means 1,000 mm (or 1 meter) in the actual structure.
These scales are commonly used in fields like architecture, civil engineering, and industrial design. The choice of scale depends on the size of the object or structure and the level of detail required. For small, detailed components, a scale like 1:10 or 1:5 may be used; for buildings or site plans, 1:50, 1:100, or even 1:500 may be more appropriate. Because all measurements are based on tens, metric scales are especially efficient for layout, dimensioning, and communication—whether on paper or in digital formats like CAD.
The PDF below is a printable set of metric scales designed to be printed 1:1 on standard US A-size (8.5 x 11) paper.