The Ultimate Guide to Index Card Sizes
Updated: Mar 1
Paper index cards are widely loved and used across the world and come in a variety of sizes. The most common size in the USA is 3" x 5" (3x5). The second most popular is 4" x 6" (4x6). Other sizes include 5x8 and of course both larger and smaller specialty cards. These sizes are also the most popular in the UK and rest of the world. What sizes are index cards and which size is best for you depends mainly on how you intend to use them as we discuss in this article.
Index Card Sizes
Size In Inches
Size in Centimeters
Size in Millimeters
3 x 5
3 x 5 in
7.62 x 12.7 cm
76.2 x 127 mm
4 x 6
4 x 6 in
10.16 x 15.24 cm
101.6 x 152.4 mm
5 x 8
5 x 8 in
12.7 x 20.32 cm
127 x 203.2 mm
6 x 9
6 x 9 in
15.24 x 22.86 cm
152.4 x 228.6 mm
In today's increasingly online environment the index card remains an important part of the working toolset. Do not be fooled by their small sizes - the index card is a powerful tool for both business and study to take notes, organize information and share with colleagues. In this article we review for you all the different index card sizes available (at the time of writing in 2023), the best use-case for each size, and the pros and cons of different sizes.
What are the Different Sizes of Index Cards?
Here is a definitive list of different card sizes. Please tell us if we have missed one!
3 x 5 inches
4 x 6 inches (see A6)
5 x 8 inches
2 x 3 inches (see A8)
2.2 x 2.5 inches
2 x 3.5 inches
5 x 7 inches
6 x 9 inches
A6 size (107mm x 153mm) or (4.1 x 5.8 inches)
A7 size (74 mm x 105 mm) or (2.9 x 4.1 inches)
A8 size(52mm x 74mm) or (2.0 x 2.9 inches)
While there are distinct card sizes, you can see some similar items like the close relationship between 4 x 6 and the A6 size for instance.
Summary of Use Cases for Index Cards
Popular Use Cases
3 x 5
Flashcards, Study Aids, Quick Notes, Storyboards, Research
4 x 6
Flashcards, Recipes, Speaking Notes
5 x 8
Note Taking, Presentations, Drawing
3 x 5 Index Cards
3 x 5 index cards (also referred as '3x5' or 3" by 5") are three inches tall by five inches wide (76.2 by 127.0 mm) and are by far the most common size - whether as ruled index cards or blank cards.
They typically look like this - this is an example of a pack of Oxford brand ruled index cards.
A 3 x 5 size ruled index card is great for taking notes, using for flash cards and storing small amounts of information like small to do lists or shopping lists. They are by far the most popular - in our research we found that the 3x5 index card is the most popular form available in store both lined or as blank index cards. We were recently at a CVS Pharmacy in West Los Angeles and you can see an example of a stack they had in stock.
4 x 6 Index Cards
4 x 6 index cards (also referred as ' 4x6' or 4" by 4") are four inches tall by six inches wide (101.6mm by 154.4 mm)
They typically look like this:
Usually available ruled, index cards in white measure 4x6 inches and the slightly larger size helps to organize larger lists and notes, to record presentation notes, store project research, manage projects, and store recipes for instance.
These are by and large interchangeable with people using a 3 x 5 size. They also seem to be more popular and the standard size in the UK.
An Amazon search between amazon.com and amazon.co.uk shows that the #1 index card size shown in the USA is 3 x 5 inches size, yet the same search query on amazon.co.uk brings up 4 x 6 inches size first also similar but not exactly the same as A6 size (4.1 x 5.8 inches). Interesting right? It shows that across the world different sizes become more standard for a variety of reasons and cultural history.
Is an Index Card 4x6?
Not Always. While the Oxford rulers' white index card measures four inches by six inches (4 x 6), that is not the only standard size. The typical standard index card size in the United States is three inches by five inches (3 x 5). They can come in a variety of sizes - if you visit your local stationery store in the office supplies / office products section you will see.
What Size are Large Index Cards?
Larger index cards are seen in the size range of 5"x 7", 5"X8" and 6" x 9".
These tend to be used for larger projects or display purposes.
What is the Largest Index Card?
In our research we found the largest 'index cards' to be 8.5" x 11" - but this is the US standard letter size. True 'largest' we would say is 6 x 9 inches like this:
What is the Thickness of an Index Card?
Index Card physical size is also determined by the thickness of the card. Thickness of an index cards ranges from 11pt to 25 pt (0.011" to 0.025"). The thickness of a card is often overlooked and can dramatically affect the perceived user experience and use case desired. Many people prefer the heavy weight card so it feels solid in the hand and more durable.
In our research we found the following average card thickness for the different sizes to be as follows:
Standard: 11pt thickness (0.011") Heavyweight Oxford brand. 0.011" is also referred to as 100lb stock. Heavyweight thickness index cards
Thin: You can get thinner ones, 7pt, 0.007" but user reviews indicate that these are too thin to be used as flashcards since the paper is too thin and your answer on the back of the card shows - be careful when selecting the right index card thickness and check the thickness. On the other hand, if you are using them as a pack in your back pocket to take quick notes then you might prefer a thinner card. Here is example of thin index cards
Thick: If you are looking for really thick cards look for thickness greater than about 100lb card stock (greater than 11pt). You can find some cards with 14pt (0.014") and higher. For example 17pt index cards
Some people even say that the heavyweight cards are not a good as they used to be in the old days, but this is what the tradeoff is in using paper cards today and trying to be economical and also saving the environment and trees. A better alternative is to use an app to create digital index cards using an app like NoteDex that creates life-like index cards on your computer and save paper!
Tips for Choosing the Right Index Card Size
To pick the right paper index card size for you determine what you need to do with the index card and also how you want the card to feel in your hand (or your back pocket!)
If you are using index cards for small notes or data or as flashcards, then 3x5 size is good - but don't forget to check the thickness - especially if you are writing answers on the back of the card.
If you want to write more information - such as study notes, use for project management, recipes, or use as visual aids, you might prefer a larger size like 4x6 or 5x8 so they can be seen easily such as on a wall or spread out on a table.
Do you need a particular brand shop version? No, we don't think so as long as it meets your size and thickness criteria. You can find good index cards in nearly any store today, and of course in all the office products stores such as Office Depot, Walmart, or online at Amazon.
What about printing index cards? If the size fits your printer then it will also be important to check if the paper is too thin (or too thick) to pass through the printer. Some printers also will on only print one side, others two sides, but they will move the paper on its rollers usually so the thickness will also be a consideration.
Paper index cards still remain today an amazing tool to help capture ideas and share information. As you can see there are many considerations to pick the right size of index card for you.
If you like using index cards you might also consider using an online index card tool like NoteDex where you can create, share and print an unlimited amount of cards - and no trees will be used!