The multiplication sign (×), also known as the times sign or the dimension sign, is a mathematical symbol used to denote the operation of multiplication, which results in a product.^[1] While similar to a lowercase X (x), the form is properly a four-fold rotationally symmetric saltire.^[2]

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The symbol is also used in botany, in botanical hybrid names.

The earliest known use of the × symbol to represent multiplication appears in an anonymous appendix to the 1618 edition of John Napier's Mirifici Logarithmorum Canonis Descriptio.^[3] This appendix has been attributed to William Oughtred,^[3] who used the same symbol in his 1631 algebra text, Clavis Mathematicae, stating:

"Multiplication of species [i.e. unknowns] connects both proposed magnitudes with the symbol 'in' or ×: or ordinarily without the symbol if the magnitudes be denoted with one letter."^[4]

Two earlier uses of a ✕ notation have been identified, but do not stand critical examination.^[3]

In mathematics, the symbol × has a number of uses, including

• Multiplication of two numbers, where it is read as "times" or "multiplied by"^[1]
• Cross product of two vectors, where it is usually read as "cross"
• Cartesian product of two sets, where it is usually read as "cross"^[5]
• Geometric dimension of an object, such as noting that a room is 10 feet × 12 feet in area, where it is usually read as "by" (e.g., "10 feet by 12 feet")
• Screen resolution in pixels, such as 1920 pixels across × 1080 pixels down. Read as "by".
• Dimensions of a matrix, where it is usually read as "by"
• A statistical interaction between two explanatory variables, where it is usually read as "by"

In biology, the multiplication sign is used in a botanical hybrid name, for instance Ceanothus papillosus × impressus (a hybrid between C. papillosus and C. impressus) or Crocosmia × crocosmiiflora (a hybrid between two other species of Crocosmia). However, the communication of these hybrid names with a Latin letter "x" is common, when the actual "×" symbol is not readily available.

The multiplication sign is also used by historians for an event between two dates. When employed between two dates – for example 1225 and 1232 – the expression "1225×1232" means "no earlier than 1225 and no later than 1232".^[6]

A monadic × symbol is used by the APL programming language to denote the sign function.

The lower-case Latin letter x is sometimes used in place of the multiplication sign. This is considered incorrect in mathematical writing.

In algebraic notation, widely used in mathematics, a multiplication symbol is usually omitted wherever it would not cause confusion: "a multiplied by b" can be written as ab or a b.^[1]

Other symbols can also be used to denote multiplication, often to reduce confusion between the multiplication sign × and the common variable x. In some countries, such as Germany, the primary symbol for multiplication is the "dot operator" ⋅ (as in a⋅b). This symbol is also used in compound units of measurement, e.g., N⋅m (see International System of Units#Lexicographic conventions). In algebra, it is a notation to resolve ambiguity (for instance, "b times 2" may be written as b⋅2, to avoid being confused with a value called b₂). This notation is used wherever multiplication should be written explicitly, such as in "ab = a⋅2 for b = 2"; this usage is also seen in English-language texts. In some languages, the use of full stop as a multiplication symbol, such as a.b, is common when the symbol for decimal point is comma.

Historically, computer language syntax was restricted to the ASCII character set, and the asterisk * became the de facto symbol for the multiplication operator. This selection is reflected in the numeric keypad on English-language keyboards, where the arithmetic operations of addition, subtraction, multiplication and division are represented by the keys +, -, * and /, respectively.

• U+00D7 × MULTIPLICATION SIGN (×)

Other variants and related characters:

• U+002A * ASTERISK (*, *)
• U+2062 INVISIBLE TIMES (⁢, ⁢) (a zero-width space indicating multiplication)
• U+00B7 · MIDDLE DOT (·, ·, ·) (the interpunct, may be easier to type than the dot operator)
• U+2297 ⊗ CIRCLED TIMES (⊗, ⊗)
• U+22C5 ⋅ DOT OPERATOR (⋅)
• U+2715 ✕ MULTIPLICATION X
• U+2716 ✖ HEAVY MULTIPLICATION X
• U+2A09 ⨉ N-ARY TIMES OPERATOR
• U+2A2F ⨯ VECTOR OR CROSS PRODUCT (⨯) (intended to explicitly denote the cross product of two vectors)
• U+2A30 ⨰ MULTIPLICATION SIGN WITH DOT ABOVE (⨰)
• U+2A31 ⨱ MULTIPLICATION SIGN WITH UNDERBAR (⨱)
• U+2A34 ⨴ MULTIPLICATION SIGN IN LEFT HALF CIRCLE (⨴)
• U+2A35 ⨵ MULTIPLICATION SIGN IN RIGHT HALF CIRCLE (⨵)
• U+2A36 ⨶ CIRCLED MULTIPLICATION SIGN WITH CIRCUMFLEX ACCENT (⨶)
• U+2A37 ⨷ MULTIPLICATION SIGN IN DOUBLE CIRCLE (⨷)
• U+2A3B ⨻ MULTIPLICATION SIGN IN TRIANGLE (⨻)
• U+2AC1 ⫁ SUBSET WITH MULTIPLICATION SIGN BELOW (⫁)
• U+2AC2 ⫂ SUPERSET WITH MULTIPLICATION SIGN BELOW (⫂)

• Division sign
• List of mathematical symbols
• Plus and minus signs
• Reference mark
• X mark