A3 paper Size in Inches & cm

A3 paper is 297 x 420 mm, or 11.7 x 16.5 inches. It is exactly two sheets of A4 placed side by side, which is the whole idea behind the ISO 216 “A” series: every size is half of the one above it.

This guide covers the exact A3 dimensions, how it relates to A4 and to the US tabloid size it is often confused with, and how a sheet compares to a monitor, a poster, and a folded newspaper.

Quick Answer: How Big Is A3 Paper?

A3 measures 297 x 420 mm (29.7 x 42.0 cm, 11.69 x 16.54 in). A single 80 gsm sheet weighs about 10 grams. It is twice the area of A4 and half the area of A2.

A3 Paper Dimensions at a Glance

• Size: 297 x 420 mm / 29.7 x 42.0 cm / 11.69 x 16.54 in
• Relationship: 2 x A4 (210 x 297 mm), or half of A2 (420 x 594 mm)
• Aspect ratio: 1:root 2, so folding it in half the long way gives A4 with the same proportions
• Common weights: 80 gsm (10 g), 120 gsm (15 g), 160 gsm card (20 g), 250 gsm card (31 g)

What Does A3 Paper Look Like in Size?

A3 is the size of an open newspaper page, or a large ring-binder spread flat. It is close to the visible screen area of a 19-inch monitor and a bit smaller than a 24-inch monitor’s panel. Stand it upright and it reaches from a desktop to roughly keyboard-tray height.

6 Everyday Comparisons for A3 Paper

1. Two A4 sheets side by side are exactly A3. This is the cleanest way to picture it.
2. US Tabloid / Ledger paper (279 x 432 mm, 11 x 17 in) is close but not identical: 18 mm narrower and 12 mm longer than A3.
3. A 19-inch 16:10 monitor has a viewable area of about 410 x 256 mm, similar width to A3, shorter.
4. A standard cereal box front panel is roughly A4; two of them stacked approximate A3.
5. A vinyl record sleeve (about 315 x 315 mm) is close to A3’s width but square.
6. A car number plate (EU, 520 x 110 mm) is longer and much shorter.

A3 Paper Size in Different Units

How the A Series Works

A0 is defined as one square metre of paper with sides in the ratio 1:root 2. Cutting A0 in half across the long side gives A1 with the same ratio; halving again gives A2, then A3, then A4, and so on. Because the ratio is preserved, you can enlarge A4 artwork to A3 at exactly 141% or shrink A3 to A4 at 71% with no cropping. A3 is the third cut down from A0.

Common Mistakes When Comparing A3 Paper

1. Treating A3 and Tabloid as the same. They are close (both “double letter/A4”), but A3 is 297 x 420 mm and Tabloid is 279 x 432 mm.
2. Assuming A3 is twice as long as A4. It is twice the area. A3’s long side (420 mm) equals A4’s long side rotated, and A3’s short side (297 mm) equals A4’s long side.
3. Forgetting orientation. “A3” is a size, not a direction; it can be portrait or landscape.
4. Using the wrong DPI for pixels. 3508 x 4961 px is A3 at 300 DPI; at 72 DPI it is only 842 x 1191 px.
5. Ignoring paper weight. A 250 gsm A3 sheet weighs three times an 80 gsm one, which matters for postage and printers.

Frequently Asked Questions

How big is A3 paper in cm?

29.7 x 42.0 cm.

How big is A3 in inches?

11.69 x 16.54 inches.

Is A3 double A4?

Yes. Two A4 sheets side by side equal one A3 sheet.

Is A3 the same as 11 x 17 (Tabloid)?

No. Tabloid is 11 x 17 in (279 x 432 mm); A3 is 297 x 420 mm. Similar, not identical.

How much does an A3 sheet weigh?

About 10 g at 80 gsm; more for heavier stock.

What is A3 used for?

Posters, spreadsheets, technical drawings, double-page layouts, and children’s artwork.

How do I scale A4 to A3?

Enlarge to 141% (or scale A3 down to A4 at 71%). The proportions match exactly.

Final Takeaway

A3 paper is 297 x 420 mm (11.69 x 16.54 in) and weighs about 10 grams per 80 gsm sheet. It is exactly two A4 sheets, it shares A4’s 1:root 2 proportions so it scales cleanly, and it is close to but not the same as the US Tabloid size.