Index card
An index card is a small, rectangular piece of thick paper or card stock, typically measuring 3 by 5 inches (76 by 127 mm), designed for recording, organizing, and storing concise bits of information such as notes, references, or data entries.[1] These cards are often ruled or blank and can be arranged in boxes or files for easy sorting and retrieval, forming systems like card catalogs or personal indexes.[2] The origins of index cards trace back to the 18th century, when Swedish botanist Carl Linnaeus adapted standardized slips of paper—possibly inspired by playing cards—for cataloging plant species in his taxonomic work, enabling flexible reorganization of information.[3] By the late 1700s, libraries began implementing card-based catalogs, with the Viennese Imperial Library creating one containing 300,000 slips by 1780, marking a shift from bound volumes to modular systems for knowledge management.[2] Standardization advanced in the 19th century; American librarian Melvil Dewey established uniform 3-by-5-inch cards in 1877 through his Library Bureau company, which also promoted their use in offices and businesses for efficient record-keeping.[2] In the 1920s, index cards revolutionized administrative practices in Europe, particularly in Germany, where they were adopted for production tracking, sales management, and government population registries, creating specialized roles like "Karteiführer" (card-file operators).[4] Index cards have been employed across diverse fields for their portability and adaptability. In libraries and archives, they powered card catalogs until the digital era, facilitating quick searches via alphabetical or subject ordering.[2] Scholars and writers, including Vladimir Nabokov, used them for note-taking and outlining complex works, with Nabokov plotting novels like Pale Fire (1962) on such cards to allow nonlinear arrangement.[3] In law enforcement, 19th-century police adopted them for biometric records, classifying traits like height and eye color to aid investigations.[3] Businesses and educators continue to value them for tasks like recipe storage, study aids, and brainstorming, as seen in J.C. Hall's use of 3-by-5-inch cards to develop Hallmark greeting cards in the early 20th century.[3] Despite the rise of digital alternatives, index cards persist in creative and analog workflows for their tactile benefits and resistance to obsolescence.[2]Physical Characteristics
Standard Dimensions and Sizes
Index cards are typically produced in rectangular shapes with straight edges, though some variations feature rounded corners to enhance durability and prevent wear in filing systems. The thickness of standard index cards is generally measured in pounds of card stock weight, ranging from 65 lb for lighter, more flexible cards to 110 lb for heavier, more rigid ones, ensuring they can withstand frequent handling without bending or tearing.[5] The most common size in the United States is 3 by 5 inches (76 by 127 mm), which was adopted as the 'postal size' due to its similarity to early postal card dimensions and became the predominant standard for library cataloging.[6] Other widely used U.S. sizes include 4 by 6 inches (102 by 152 mm) for moderately larger notes and 5 by 8 inches (127 by 203 mm) for more detailed entries. In Europe and regions adhering to metric standards, the ISO A7 size of 74 by 105 mm serves as an equivalent for compact indexing.[7][8] Historical standardization began in 1877 when the American Library Association adopted two sizes—2 by 5 inches and 3 by 5 inches—at its inaugural conference to promote uniformity in catalog sharing among libraries, with the 3 by 5 inch format eventually prevailing due to its balance of compactness and legibility. The Library of Congress further solidified this in 1901 by initiating the distribution of pre-printed 3 by 5 inch catalog cards, facilitating nationwide interoperability in library systems. Larger sizes like 4 by 6 and 5 by 8 inches emerged later as extensions for specialized applications requiring more space.[6] These sizes maintain aspect ratios close to 3:5 (0.6) for the 3 by 5 inch card, approximately 2:3 (0.667) for 4 by 6 inches, and 5:8 (0.625) for 5 by 8 inches, allowing consistent stacking and sorting in drawers or boxes. Uniform dimensions across cards enable seamless integration in filing systems, reducing errors in organization and supporting efficient retrieval in both manual and semi-automated setups.[6][7]| Size | Imperial Dimensions (inches) | Metric Dimensions (mm) | Common Use |
|---|---|---|---|
| Standard | 3 × 5 | 76 × 127 | Compact notes, library catalogs |
| Medium | 4 × 6 | 102 × 152 | Flashcards, outlines |
| Large | 5 × 8 | 127 × 203 | Detailed records, bibliographies |
| Metric Equivalent | 2.9 × 4.1 (A7) | 74 × 105 | European indexing |