A triangular scale is a ruler that has a 3-lobed cross-section with 6 different types of scales on the edges (2 on each face) used for measuring and preparing scale drawings such as blueprints and maps. It is also called an architect’s scale. Some types have a bamboo core and are coated with other material on the surface. Others are made of synthetic resin or aluminum. But they are usually 15cm or 30cm long. They should not be confused with set squares (triangular squares) which have a different shape and function altogether.

Most blueprints are drawn scaled down rather than in their actual size. A triangular scale allows the user to check the dimensions without having to do the calculations to convert the measurements. For example, when drawing a 1:50 blueprint, to represent a line which is 1.8m in actual size, one would have to divide 1800mm by 50 to get 36mm before drawing the line if only an ordinary ruler is available. With a triangular scale, 1:50 scale markings are already provided so the user can simply look for 1.8 on the markings. The scale factor is indicated on the left. Using the wrong scale will result in major errors so the scale factor should be checked carefully before measuring. In some triangular scales, the three faces are painted in different colors to prevent mistakes like these.

A single triangular scale is scored with 6 different types of scales but the combination depends on whether it is for architectural use or for land and property surveys, etc. This needs to be confirmed at the time of purchase. There is also a more portable fan shaped five blade scale ruler which has the same functions. A triangular scale is a tool for checking the dimensions and scale and should not be used to draw lines as an alternative for a ruler. Triangular scales can be purchased at drafting supply and art supply stores.