A4 vs Letter Paper Size — The Complete Guide to Paper Dimensions
If you've ever tried to print a document formatted for US Letter on A4 paper (or vice versa), you know the sizes don't match. The margins shift, the layout breaks, and everything looks slightly off.
That's because A4 and US Letter are different standards with different dimensions, used by different parts of the world.
A4 vs Letter: Side by Side
| Property | A4 | US Letter |
|---|---|---|
| Width | 210 mm (8.27") | 216 mm (8.50") |
| Height | 297 mm (11.69") | 279 mm (11.00") |
| Area | 62,370 mm² | 60,264 mm² |
| Aspect ratio | 1:√2 (1:1.414) | 1:1.294 |
| Used in | Most of the world | US, Canada, Mexico, Philippines |
A4 is taller and narrower. Letter is shorter and wider. A4 has about 3.5% more surface area.
The difference in width is only 6 mm (about a quarter inch) — easy to miss visually. The difference in height is 18 mm (about three-quarters of an inch) — noticeable when you stack the two sheets.
The ISO A-Series: A0 Through A10
A4 belongs to the ISO 216 standard, which defines the entire A-series. The clever property of this system: each size is exactly half the area of the next larger size, achieved by cutting the longer side in half.
| Size | Dimensions (mm) | Dimensions (inches) | Common Use |
|---|---|---|---|
| A0 | 841 × 1189 | 33.1 × 46.8 | Technical drawings, posters |
| A1 | 594 × 841 | 23.4 × 33.1 | Flip charts, large posters |
| A2 | 420 × 594 | 16.5 × 23.4 | Posters, diagrams |
| A3 | 297 × 420 | 11.7 × 16.5 | Tabloid printing, large forms |
| A4 | 210 × 297 | 8.27 × 11.69 | Standard documents, printing |
| A5 | 148 × 210 | 5.83 × 8.27 | Notebooks, booklets |
| A6 | 105 × 148 | 4.13 × 5.83 | Postcards, pocket books |
| A7 | 74 × 105 | 2.91 × 4.13 | Playing cards, small notes |
| A8 | 52 × 74 | 2.05 × 2.91 | Business cards (in some countries) |
The mathematical relationship: all A-series sizes have an aspect ratio of 1:√2 (approximately 1:1.414). This means folding an A4 sheet in half gives you two A5 sheets with identical proportions.
North American Paper Sizes
The US, Canada, and a few other countries use a different system:
| Size | Dimensions (mm) | Dimensions (inches) | Common Use |
|---|---|---|---|
| Letter | 216 × 279 | 8.5 × 11.0 | Standard documents |
| Legal | 216 × 356 | 8.5 × 14.0 | Legal documents, contracts |
| Tabloid / Ledger | 279 × 432 | 11.0 × 17.0 | Newspapers, large spreadsheets |
| Executive | 184 × 267 | 7.25 × 10.5 | Memos, smaller documents |
| Half Letter | 140 × 216 | 5.5 × 8.5 | Flyers, half-fold brochures |
Unlike the A-series, these sizes don't follow a mathematical pattern. They evolved from historical conventions rather than being designed as a system.
Which Countries Use Which Standard?
A4 (ISO 216): Almost everywhere — all of Europe, Asia, Africa, South America, Australia, and most of Central America.
US Letter (ANSI): United States, Canada, Mexico, the Philippines, and a few Caribbean nations.
If you're formatting a document for an international audience, A4 is the safer choice. A document designed for A4 will print on Letter paper with slightly wider margins. The reverse — Letter formatted for A4 — may clip content at the bottom.
Using Paper for Screen Calibration
A sheet of A4 paper is a surprisingly useful calibration tool for larger screens, especially tablets and laptops:
Why it works well:
- The dimensions are precisely standardized (210.0 × 297.0 mm, tolerance ±1.5 mm)
- It's large enough for very precise alignment on bigger screens
- Most people have printer paper readily available
How to calibrate with A4 paper on Screen Ruler Online:
- Select "A4 Paper" from the calibration reference objects
- Place the sheet against your screen (use the width — 210 mm — for horizontal calibration)
- Adjust the slider until the on-screen reference matches the paper edge
- Done — your ruler is calibrated
Limitations:
- Paper is flexible and can bow slightly against the screen — press it flat
- On small phone screens, A4 paper is too large to serve as a useful reference; use a credit card instead
- If your paper is standard copy paper (80 gsm), it should be dimensionally accurate; specialty or hand-cut paper may not be
Other Standard Sizes You Might Need
Envelope Sizes
| Size | Dimensions (mm) | Fits |
|---|---|---|
| C4 | 229 × 324 | A4 unfolded |
| C5 | 162 × 229 | A4 folded once |
| C6 | 114 × 162 | A4 folded twice |
| DL | 110 × 220 | A4 folded in thirds |
| #10 (US) | 105 × 241 | Letter folded in thirds |
Photo Print Sizes
| Size | Dimensions (mm) | Dimensions (inches) |
|---|---|---|
| 4R | 102 × 152 | 4 × 6 |
| 5R | 127 × 178 | 5 × 7 |
| 6R / A5 | 152 × 203 | 6 × 8 |
| 8R | 203 × 254 | 8 × 10 |
| A4 | 210 × 297 | 8.27 × 11.69 |
Measure Any Paper Size on Screen
Need to verify the dimensions of a document, photo, or envelope? Open Screen Ruler Online, calibrate with a credit card or A4 sheet, and measure directly on your screen. Works on any device, no download needed.
If a printable ruler is easier for the task at hand, the printable ruler PDF generator outputs millimeter and inch scales sized to fit A4 or Letter. The tools page lists the other free utilities — protractor for angles, aspect ratio calculator, device specs database — in case the measurement task spirals beyond paper.
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