3x5

3x5 (three by five) is a shorthand used to denote a quantity or a two-dimensional dimension formed by a group of three units and a group of five units. In arithmetic, 3×5 equals 15. The expression also appears in various contexts to describe the size or shape of an object, typically stated as width by height or rows by columns.

In mathematics, a 3×5 matrix has three rows and five columns and contains fifteen entries. Such a matrix defines a linear transformation from R5 to R3. The transpose of a 3×5 matrix is a 5×3 matrix; multiplication rules require matching inner dimensions (for A as a 3×5 matrix and B as a 5×p matrix, the product AB is a 3×p matrix).

In everyday use, 3×5 inch cards are a standard size for index cards and flash cards. They are commonly used in education for studying and organizing information, and are smaller than many business cards and standard photographic formats. Other common applications include layout planning and design grids described as having 3 by 5 dimensions.

The term is sometimes used simply as a shorthand for "three by five" in discussions of grids, matrices, or measurements, and is typically written using the multiplication sign (3×5) or the word "3 by 5".