Card Making Systems & Standards

Converting Between Measurement Systems

CardCalc.app was created to help the international crafting community easily convert between metric and imperial measurements. When crafters from different regions share ideas and tutorials, the challenge of translating measurements can be frustrating.

Converting between systems often results in awkward decimal measurements:

• A US A2 card (4¼ × 5½") converts to 108 × 140mm
• An ISO A6 card (105 × 148mm) converts to 4.13 × 5.83"

These decimal measurements can be impractical when using rulers marked in fractions of inches or when trying to visualize sizes. CardCalc.app provides practical conversions that work for crafters using either system.

Card Size Considerations for Crafters

While paper manufacturing and printing industries have established size standards, card makers typically approach sizing from a practical perspective:

• Postage Requirements: Postal services often have specific size and weight restrictions that affect postage rates
• Envelope Availability: The availability of envelopes usually dictates card dimensions
• Material Efficiency: How many cards can be cut from a single sheet of cardstock

For most card makers, the process often begins with selecting an envelope size that meets postal requirements, then designing a card to fit within that envelope.

Why Card Sizes Are Confusing

Card size terminology can be confusing due to:

• Different paper standards used globally (ISO vs. US system)
• Similar naming conventions (A2, A4, etc.) referring to completely different sizes
• Conversion between metric and imperial measurements resulting in impractical decimal numbers

That's why we built CardCalc.app: This tool helps crafters quickly convert between measurement systems, find compatible envelope sizes, and calculate layer dimensions - regardless of which paper system you use. Our calculator displays dimensions in both practical ⅛ inch fractions for imperial measurements and precise millimeters for metric.

ISO 216 A-Series (International Standard)

The ISO A-Series is used throughout most of the world (except North America). This elegant system has a mathematical basis: each size is exactly half the area of the previous size, and all sizes maintain the same aspect ratio of 1:√2 (approximately 1:1.414).

The common A4 paper (210 × 297mm) is the standard office paper size in most countries. When folded in half, it becomes A5. When A5 is folded in half, it becomes A6.

Popular Card Sizes in the ISO System:

• A6: 105 × 148mm (4⅛ × 5⅞") - A common greeting card size internationally
• A5: 148 × 210mm (5⅞ × 8¼") - Used for larger cards or invitations

In the ISO system, envelope sizes typically use "C" designations (C4, C5, C6), which are designed to fit their corresponding A-series paper sizes.

US Announcement Sizes (North American Standard)

The US system is primarily based on envelope sizes that became standardized for formal correspondence and announcements. Unlike the ISO system, which focuses on paper sheets, the US announcement card system originated from common envelope dimensions used for social correspondence.

The basis for most US cardmaking is standard Letter-size paper (8½ × 11"), which doesn't share the mathematical relationship of the ISO system. Instead, common card sizes evolved based on how many cards could be cut from a single sheet of Letter paper, and what envelope sizes were commonly available.

Common US Card Sizes:

• A2: 4¼ × 5½" (108 × 140mm) - The most popular card size for US crafters
• A7: 5 × 7" (127 × 178mm) - More room to work with

Why is A2 so Popular with US Card Makers?

The A2 size (4¼ × 5½") is widely used by US card makers for these practical reasons:

• Material efficiency: You can get two complete cards from one piece of 8½ × 11" cardstock
• Envelope availability: A2 envelopes (also called "invitation envelopes") are readily available and inexpensive
• Postage economy: This size typically mails at standard first-class rates in the US
• Design efficiency: Four card fronts can be cut from one sheet with minimal waste
• Compact size: Smaller than traditional greeting cards but large enough for meaningful design elements

Other Popular Card Sizes

Beyond the standard systems, certain sizes have become popular among crafters worldwide:

• Slimline: 3½ × 8½" (89 × 216mm) - Fits in standard #10 business envelopes
• Mini Slimline: 3 × 6" (76 × 152mm) - A smaller version gaining popularity, though measurements can vary by craft company (some use 3½ × 6")

Note: The card sizes we use on our site are a best guess for the common crafting sizes. As with the Mini Slimline example above, there can be variation between different craft companies, especially for specialty dies and templates.

Practical Considerations for Card Makers

Postal Regulations

Different countries have varying postal requirements that impact card design:

• Size restrictions: Most postal services have minimum and maximum dimensions for standard mail
• Thickness and weight: Dimensional elements and heavy embellishments may require additional postage
• Square cards: In some countries (like the US), square-shaped mail requires additional postage

Working Across Different Systems

International crafters have developed practical approaches when working with tutorials and supplies from different regions:

• Envelope-first design: Start with locally available envelope sizes, then design cards to fit those dimensions
• Adapted sizing: Many crafters in Australia, New Zealand, and Europe use modified dimensions that maximize material usage. For example, cutting A4 sheets into 5½ × 4⅛" pieces allows creating four card fronts from one A4 sheet with minimal waste.
• Focus on proportions: When following international tutorials, adapt the proportional layout rather than exact measurements