- Metric rulers:
- 15 centimeters (cm) / 150 millimeters (mm)
- 20 cm / 200 mm
- 30 cm / 300 mm
- Imperial rulers:
- 6 inches (in)
- 12 in
- 18 in
- 24 in
However, there are rulers available in lengths that differ from these common sizes. It's best to refer to the markings on the ruler itself to determine its specific length.