What is the difference between A4 and US Letter?

A4 (210 × 297 mm) is slightly narrower and taller than US Letter (215.9 × 279.4 mm / 8.5 × 11 in). A4 is the international standard while Letter is used mainly in the United States and Canada.

How are ISO A series sizes related to each other?

Each A size is exactly half the area of the previous one. Fold an A3 sheet in half and you get A4; fold A4 and you get A5. The ratio of width to height is always 1 : √2 (approximately 1 : 1.414), which preserves proportions when halving.

What is the C series used for?

The C series defines envelope sizes. A C4 envelope fits an unfolded A4 sheet; a C5 envelope fits A4 folded once in half; and a C6 envelope fits A4 folded into quarters. This makes matching documents to envelopes straightforward.

What is the B series used for?

B series sizes are intermediate between consecutive A sizes and are commonly used for books, posters, and passports. A B5 page falls between A4 and A5 in size. The B series follows the same 1 : √2 ratio.

What does "to-scale" mean in the visual comparison?

The preview preserves each selected sheet's width-to-height ratio and scales it to fit the available panel. Use the numeric dimensions for comparisons between different selections.

Are these dimensions exact?

Yes. ISO 216 specifies exact integer millimeter dimensions for the A and B series, and the C series (ISO 269) dimensions are also exact integers. US sizes are defined in inches and are converted here using the exact factor 1 inch = 25.4 mm.

Paper Size Reference Chart

Browse every standard paper size — ISO A/B/C series and US formats — with dimensions in mm, cm, and inches, plus a to-scale visual comparison.

Unit:

Click a row to preview · click Compare to overlay two sizes

Series	Size	Width	Height	Actions

Visual Preview

Select a size from the table

Click a row to preview its size

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Summary

Browse every standard paper size — ISO A/B/C series and US formats — with dimensions in mm, cm, and inches, plus a to-scale visual comparison.

How it works

The table is pre-populated with ISO A0–A10, B0–B10, C0–C10, and US standard sizes.
Select a unit (mm, cm, or inches) using the toggle at the top of the table.
Click any row to highlight it and display a to-scale preview on the right panel.
Use the "Compare" button on two rows to overlay both sizes in the visual panel.
Select a row, then use the preview panel's copy control to copy its dimensions.

Use cases

Verify print dimensions before sending a document to a print shop.
Choose the right envelope or folder size for a given paper sheet.
Compare US Letter to ISO A4 when formatting documents for international audiences.
Find the correct canvas size for design software when creating print-ready artwork.
Quickly reference poster and banner dimensions for large-format printing.
Teach students about the elegant halving relationship of the ISO A series.
Check whether a specific paper fits inside a standard binder or folder.
Confirm envelope (C series) sizing matches the letter paper being mailed.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu