英寸（英语：inch，众数：inches；缩写为 in 或 ″）（读音：cùn或yīngcùn），或英吋，简称吋，是使用于英国（联合王国）及其前殖民地和英联邦的长度单位，美国、加拿大、澳大利亚等前英国殖民地国家也用。

英寸的常用简写为 in或 "。

“吋”是近代新造的复音汉字（即单个汉字发两个音节，类似单位还有“哩”等），发音同“英寸”，借用中国传统的长度单位“寸”，并加口旁以示区别。中国大陆目前已很少使用单个汉字“吋”作单位，多直接使用词语“英寸”。

An inch (plural: inches; abbreviation or symbol: in or ″ – a double prime) is a unit of length in the imperial and United States customary systems of measurement. Historically, an inch was also used in a number of other systems of units. Traditional standards for the exact length of an inch have varied in the past, but since July 1959, when the international yard was defined as 0.9144 metres, the international inch has been exactly 25.4 mm. There are 12 inches in a foot and 36 inches in a yard.