A4 paper measures 210 × 297 millimeters, or 21 × 29.7 centimeters. In inches, that is approximately 8.27 × 11.69. A4 is narrower and taller than US Letter, which measures exactly 8.5 × 11 inches. The difference matters when a document must fit a printer tray, envelope, binder or preprinted form.
Start with the size requested by the recipient or print provider. Then make the document settings and the physical paper agree. A familiar-looking sheet is not enough: A4 and Letter can look nearly interchangeable on a desk but leave different space at the edges of a printed page.
A-series paper sizes in millimeters and inches
The A-series belongs to the paper-size system described by ISO 216. The table gives the specified nominal millimeter dimensions, with the shorter edge first. The inch values are calculated from those dimensions and rounded to two decimal places; they are not alternative exact definitions.
| Size | Millimeters | Inches, rounded |
|---|---|---|
| A0 | 841 × 1189 | 33.11 × 46.81 |
| A1 | 594 × 841 | 23.39 × 33.11 |
| A2 | 420 × 594 | 16.54 × 23.39 |
| A3 | 297 × 420 | 11.69 × 16.54 |
| A4 | 210 × 297 | 8.27 × 11.69 |
| A5 | 148 × 210 | 5.83 × 8.27 |
| A6 | 105 × 148 | 4.13 × 5.83 |
| A7 | 74 × 105 | 2.91 × 4.13 |
| A8 | 52 × 74 | 2.05 × 2.91 |
| A9 | 37 × 52 | 1.46 × 2.05 |
| A10 | 26 × 37 | 1.02 × 1.46 |
The millimeter values match Hohner’s paper conversion reference. For custom dimensions, divide millimeters by 25.4; the millimeters-to-inches guide explains that conversion and when rounding matters. Keep the original metric dimensions when ordering precisely cut paper.
Why A3, A4 and A5 keep the same shape
The A-series proportions are built around a short-edge-to-long-edge ratio of 1 to the square root of 2, approximately 1:1.414. Halving a rectangle with this ratio across its longer dimension produces two smaller rectangles with the same proportions. A larger number therefore means a smaller sheet.
An A3 sheet measures 297 × 420 mm. Dividing its 420 mm edge in half gives two 210 × 297 mm A4 sheets. Halving A4 produces the next size, A5, listed as 148 × 210 mm. Notice that half of 297 is 148.5, not 148: the standardized whole-millimeter dimensions mean the halving relationship is not exact at every step. Use the listed dimensions rather than repeatedly dividing and rounding your own measurements.
The shared proportions are useful when resizing artwork between A-series formats. In ideal geometry, one size down uses about 70.7% of the original linear dimensions; one size up uses about 141.4%. Half the area does not mean half the width. For a finished print, check the software preview and the printer’s available margins before relying on a preset percentage.
A4 versus US Letter, Legal and Tabloid
| Format | Millimeters | Inches |
|---|---|---|
| A4 | 210 × 297 | 8.27 × 11.69, rounded |
| US Letter | 215.9 × 279.4 | 8.5 × 11 |
| US Legal | 215.9 × 355.6 | 8.5 × 14 |
| Tabloid / Ledger | 279.4 × 431.8 | 11 × 17 |
Compared with Letter, A4 is 5.9 mm narrower and 17.6 mm taller. Neither sheet contains the other at full size in the same orientation. A Letter layout can extend beyond A4’s side edges, while an A4 layout can extend beyond Letter’s top or bottom edges. Whether content is affected depends on its placement and margins.
Legal shares Letter’s width but adds three inches of length. Tabloid’s 11 × 17-inch dimensions are also different from A3’s 297 × 420 mm. Check the actual format rather than treating these names as regional translations of one another.
Portrait and landscape do not change the paper size
Portrait A4 is 210 mm wide and 297 mm high. Landscape A4 is 297 mm wide and 210 mm high. Turning the sheet changes the orientation, not its physical dimensions or area. Choose landscape when a wide layout needs it, then inspect the page again because text, tables and images may move when the document is reformatted.
Paper size also does not specify paper thickness, weight or finish. A4 copy paper and A4 card have the same nominal edge lengths but may require different printer settings or feeding methods. Check both the size and the supported media type.
Choose paper size separately from print scaling
There are three settings to distinguish: the document’s page size, the output paper size and the scale of the content. Changing the selected tray paper to Letter does not, by itself, guarantee that an A4 document will be reduced safely. Application and printer-driver behavior varies.
In Adobe Acrobat’s page-sizing controls, Fit adjusts the page to the printable area. Actual size prints without scaling, so content outside the printable area can be cropped. Shrink oversized pages reduces large pages without enlarging smaller ones. These are Acrobat options; another app may use different labels or defaults.
For an ordinary document, select the paper actually loaded, review the scaling choice and inspect every edge in preview. For a template that must retain physical measurements, use the required page format and an unscaled setting, then measure a reference length on a trial print. Avoid assuming a successful print is dimensionally accurate.
Check the printer and envelope before buying paper
Look in the printer manual for supported sheet sizes, paper weights, tray requirements and any restrictions on two-sided or borderless printing. A printer that accepts A4 does not necessarily accept A3, heavy card or every envelope. Adjust the tray guides for the loaded sheets using the manufacturer’s instructions.
For mailing, decide whether the document must stay flat or can be folded. Check the envelope’s stated usable capacity and leave room for the thickness of the contents. A nominal outer envelope measurement alone does not guarantee an easy fit. Test the actual stack before ordering a large quantity.
If you need supplies, you can browse A4 printer paper on Amazon. Confirm that the listing says 210 × 297 mm, then check the paper type against your printer requirements. Matching the document, paper and settings first is simpler than correcting a whole stack of mismatched prints.
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