Equals sign (=): meaning, history, and uses

Notation and appearance

Visually the sign consists of two short parallel horizontal strokes placed at roughly the same height on the line of writing. Typography and handwriting produce minor variations, but the basic form is consistent worldwide. In character encodings modern systems represent it as a standard code point: the Unicode code point is often referenced in technical documentation Unicode, and its position in ASCII is commonly noted in information about legacy encodings ASCII and hexadecimal tables hex codes. Computer keyboards and programming environments display and accept the same glyph for many practical purposes.

History and origin

The equals sign was introduced in the 16th century to provide a concise way to state equality without repeating words. One widely cited origin is the work of an early modern mathematician who proposed two short parallel lines to indicate that two things were "equal" because, in his words, they were of the same length. Earlier mathematical traditions had described equalities verbally or used alternative notations; the two-line sign proved compact and convenient, and it gradually became standard in printed texts and then in handwritten mathematics. For background on the underlying idea of equality see equality concept.

Use in mathematics and logic

In mathematics the equals sign denotes a relation: equality is reflexive (x = x), symmetric (if x = y then y = x), and transitive (if x = y and y = z then x = z). It appears in simple arithmetic statements, in algebraic equations that define unknowns, and in identities that hold for all values of variables. Mathematicians also use the sign to express definitions and substitutions.

Use in computing and programming

Computers and programming languages use the equals sign in several related but distinct ways. Many languages use "=" for assignment (store a value in a variable) and a different form such as "==" or "===" to test equality; others adopt ":=" or specific functions for assignment and comparison. This difference between mathematical equality and computational assignment is an important distinction when learning programming. General information about computing contexts is available at computing reference.

Related symbols and distinctions

• ≡ often denotes definitional equality or congruence in number theory.
• ≈ denotes approximate equality.
• ≠ denotes inequality (not equal).
• := used in some texts to mean "is defined as".
• Programming comparisons: "==" or "===" distinguish types or strict equality in different languages.

For typography and more on graphical variants see typography and discussions of line orientation horizontal form. Further technical references and character tables are collected under encoding notes and broader symbol catalogs symbol overview, ASCII.