Is A4 the same size as US Letter?

No — A4 (210 × 297mm) is narrower and longer than US Letter (216 × 279mm, or 8.5 × 11 inches). The difference is small (a few millimeters in each dimension) but enough that documents formatted for one size will have their margins shifted or content cut off if printed directly on the other without rescaling.

Paper Size Chart: A-Series, US Sizes, and Dimensions (mm/inches)

Compare international A-series paper sizes (A0-A6) with US Letter, Legal, and Tabloid sizes, including dimensions in millimeters and inches.

Convert from

A-Series value

Convert to

Dimensions (mm): 841 × 1189

Paper Size Chart: A-Series, US Sizes, and Dimensions (mm/inches)
A-Series	Closest US Size	Dimensions (mm)	Dimensions (in)
A0	—	841 × 1189	33.1 × 46.8
A1	—	594 × 841	23.4 × 33.1
A2	—	420 × 594	16.5 × 23.4
A3	Tabloid (close)	297 × 420	11.7 × 16.5
A4	Letter (close)	210 × 297	8.3 × 11.7
A5	—	148 × 210	5.8 × 8.3
A6	—	105 × 148	4.1 × 5.8
Letter	US Letter	216 × 279	8.5 × 11
Legal	US Legal	216 × 356	8.5 × 14
Tabloid	US Tabloid	279 × 432	11 × 17

How to Measure

If you need to know whether a document will fit a specific printer or frame, compare its dimensions in millimeters or inches directly using this table — A4 and US Letter are close in size (A4 is slightly narrower and longer) but not interchangeable, so a document formatted for one will not print correctly on the other without rescaling.

Notes

The A-series follows a consistent mathematical rule: each size is exactly half the area of the size above it, folded along its longer dimension (A1 is A0 folded in half, A2 is A1 folded in half, and so on), and every size shares the same aspect ratio (1:√2). US paper sizes (Letter, Legal, Tabloid) don't follow this rule and have no consistent ratio relationship to each other.

Frequently Asked Questions

The A-series is designed so that cutting or folding a sheet in half along its longer side produces two sheets of the next size down, each with the same aspect ratio as the original. This requires the ratio of the longer side to the shorter side to be √2 (approximately 1.414) — the only ratio for which halving preserves the proportions, which is why the A-series maintains the same 'shape' at every size.

Source: ISO 216 (international paper size standard) and ANSI/US paper size conventions · see our methodology