index card 3x5 to mm Converter
Convert index card 3x5 to mm instantly with a reference conversion table.
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How to convert index card 3x5 to mm
Enter your value
Type the number of index card 3x5 you want to convert into the left box. The result in mm appears instantly in the right box. You can also type into the right box to convert in the other direction.
Use the swap button
Click the ⇄ Swap button to reverse the conversion — mm to index card 3x5. Your current value carries across so you don't have to re-enter anything.
About index card 3x5 and mm
A 3x5 index card is a standard inch-based paper size (3 inches × 5 inches), which converts to 76.2mm × 127mm using the exact 25.4mm-per-inch standard. Because a named card size describes two dimensions rather than a single linear quantity, converting it to millimeters really means converting each of the width and height separately, rather than applying one scalar multiplication factor.
Index card sizes for study, crafts, and cataloguing
Choosing the right size for flashcards
3x5 (76.2 × 127mm) is the standard size for compact flashcards and quick reference notes, while 4x6 (101.6 × 152.4mm) suits longer study notes or recipe cards, and 5x8 (127 × 203.2mm) works better for detailed outlines or larger handwriting. Knowing the metric equivalents helps when sourcing cards, sleeves, or storage boxes from suppliers that list dimensions in millimeters.
A legacy of library cataloguing
The 3x5 index card size dates back to 19th-century library card catalogues and became so standardized in offices, schools, and printing that it persists globally today, even in countries that otherwise use ISO metric paper sizes (A4, A5, A6) for everything else.
Comparing to metric paper sizes
A 3x5 card (76.2 × 127mm) is noticeably smaller than the closest ISO paper size, A6 (105 × 148mm), so the two aren't interchangeable despite both being roughly "postcard-sized." Anyone designing printable templates for both markets needs to treat these as genuinely separate sizes rather than approximating one with the other.
Frequently asked questions
How do I convert index card 3x5 to mm?
A standard 3x5 index card measures 3 inches by 5 inches, which converts to 76.2mm by 127mm using the exact 25.4mm-per-inch standard. Use the calculator above for other sizes and custom values.
What are the exact millimeter dimensions of a 3x5 index card?
A 3x5 index card is 76.2mm × 127mm exactly. Because index cards are a two-dimensional paper size, both width and height need converting separately rather than using one multiplication factor.
Is the index card 3x5 to mm converter free?
Yes, the index card 3x5 to mm converter is completely free with no sign-up required, no downloads, and it works offline once the page has loaded.
What are the other standard index card sizes?
Besides 3x5 (76.2 × 127mm), standard sizes include 4x6 (101.6 × 152.4mm) for larger flashcards and recipe cards, and 5x8 (127 × 203.2mm) for detailed notes.
Why are index cards sized in inches rather than a metric standard?
Index cards originated in the US in the late 19th century as part of library card-catalogue systems, long before ISO metric paper standards existed. The inch-based sizes remain the global standard for index cards regardless.
How does a 3x5 index card compare to an A6 sheet?
A6 paper (105 × 148mm) is noticeably larger than a 3x5 index card (76.2 × 127mm) in both dimensions. A 3x5 card remains its own distinct standard rather than mapping onto any ISO paper size.