A ruler is a stationery item and drafting tool used when drawing lines, as a guide for cutting, and for various other uses. It is available in different shapes and materials, depending on the type of lines the user wishes to draw. Some rulers have measurement gradations and can be used for measuring length. In general, those used for drawing lines and as a cutting guide are referred to as straight edges, and those used for taking measurements, rulers.

Commonly-used rulers include the straight edge for drawing straight lines and the set square. When two set squares are used in combination, they can be used to draw horizontal and perpendicular lines. Although used less frequently in recent years, when drafting, a T square is used with set squares on the drafting board to draw parallel and perpendicular lines. Another drafting instrument is the dashed-line ruler for drawing dotted or broken lines. But this is rarely used in ordinary settings. The French curve and the adjustable ruler are special tools for drawing curved lines. Some rulers have cut-out circles, ellipses, text, symbols and shapes on them. These are called templates and there are various types. The L-shaped carpenter’s square is a typical Japanese carpenter’s tool used for checking right angles, drawing lines and various other purposes. Another tool for ensuring consistency is the protractor, used to measure angles. In this way, there are countless types and uses for what we simply call the “ruler”. Rulers can be purchased at stores selling drafting tools, art supply shops and DIY stores.