If you’ve ever tried to print a poster or design a document and wondered exactly how big A3 is, you’re not alone. A3 paper measures 29.7 cm by 42.0 cm, making it twice the area of a standard A4 sheet.

4 related posts

A3 width in cm: 29.7 cm ·
A3 height in cm: 42.0 cm ·
A3 area: 0.125 m² ·
A3 vs A4 size difference: A3 is twice as large as A4 ·
A3 vs A2 size difference: A2 is twice as large as A3

Quick snapshot

1Confirmed facts
2What’s unclear
3Timeline signal
4What’s next
  • Use this guide to choose A3 for posters, diagrams, and large layouts – or compare A3 with A2 and A5 for specific projects

Here are the exact A3 dimensions in multiple units and its place in the ISO 216 standard.

Label Value
A3 width 29.7 cm (Neenah Paper)
A3 height 42.0 cm (Neenah Paper)
A3 area 0.125 m² (papersizes.io)
A3 aspect ratio 1:√2 (1.414) (Adobe)
A3 vs A4 area ratio 2:1 (Adobe)
A3 vs A2 area ratio 1:2 (Adobe)

The implication: A3 sits precisely in the middle of the A‑series range, offering a large format that scales cleanly to both smaller and larger sizes.

What is A3 size in cm?

A3 dimensions in cm, mm, and inches

The catch: these are the standard rounded values. Actual paper produced by mills may vary by fractions of a millimetre, though the difference is negligible for most projects.

How A3 fits into the A‑series paper size system

The A‑series is defined by ISO 216. A0 has an area of one square metre, and each subsequent size is half the area of the previous one while preserving the √2:1 aspect ratio (papersizes.org (paper size reference)). A3 is the fourth size in the series, exactly two steps down from A1.

The upshot

Because A3 uses the same aspect ratio as A4, scaling a design from A4 to A3 is a simple 141 % enlargement – no cropping or distortion needed.

Is A3 bigger than A4?

A3 vs A4 size comparison

A3 has exactly twice the area of A4. A4 measures 21.0 cm × 29.7 cm (Neenah Paper).

The pattern: this doubling relationship means that two A4 sheets placed side by side along the short edge form exactly one A3 sheet.

Practical differences between A3 and A4

  • A3 is commonly used for posters, diagrams, and architectural drawings
  • A4 is the standard for letters, reports, and everyday documents (papersizes.io)

Size | Width (cm) | Height (cm) | Area (m²)
A3 | 29.7 | 42.0 | 0.125
A4 | 21.0 | 29.7 | 0.0625

What this means: for a design that needs more visual impact or space for detailed information, A3 gives you double the canvas of A4 without changing the proportions.

Is A3 bigger than A5?

A3 vs A5 size comparison

A3 is four times the area of A5. A5 dimensions are 14.8 cm × 21.0 cm (Adobe).

The implication: you can fit four A5 pages on a single A3 sheet, making it ideal for booklet layouts or multi‑panel displays.

How A5 relates to A3 in the A-series

  • A5 is used for notepads and flyers
  • A3 provides the large format needed for master layouts that contain multiple A5 elements

The catch: while A3 is great for large visuals, A5 is more portable and cost‑effective for short‑form content.

Which is bigger, A3 or A2 or A1?

A1 vs A2 vs A3 size comparison

A1 is larger than A2, and A2 is larger than A3. A1 dimensions are 59.4 cm × 84.1 cm, and A2 dimensions are 42.0 cm × 59.4 cm (Neenah Paper).

The pattern: each size is half the area of the previous size. A1 covers 0.5 m², A2 covers 0.25 m², and A3 covers 0.125 m².

Understanding the A-series size progression

  • A0: 84.1 × 118.9 cm, area 1 m² (Adobe)
  • A1: 59.4 × 84.1 cm, area 0.5 m²
  • A2: 42.0 × 59.4 cm, area 0.25 m²
  • A3: 29.7 × 42.0 cm, area 0.125 m²
  • A4: 21.0 × 29.7 cm, area 0.0625 m²

What this means: if you need a poster larger than A3, you would move up to A2 or A1. The consistent aspect ratio across all sizes simplifies design and printing at any scale.

Is 40×30 cm A3?

Why 40×30 cm is not A3

A3 dimensions are 29.7 cm × 42.0 cm, not 40×30 cm. The aspect ratio of A3 is 1:√2 (approximately 1:1.414), whereas 40×30 cm has a ratio of 4:3 (Neenah Paper).

The catch: ordering a print labelled “A3” that is actually 40×30 cm would lead to cropping or distortion of your design.

Common misconceptions about A3 dimensions

  • Many people mistakenly think A3 is 40×30 cm because of approximate metric rounding
  • A3 has a specific aspect ratio of 1:√2, which 40×30 cm does not match
  • Some non‑standard paper sizes use A3 nomenclature incorrectly – always check the exact dimensions

What this means: always verify the exact dimensions (29.7 cm × 42.0 cm) before purchasing or designing for A3.

After reviewing the data and comparisons, the key takeaway is that professionals and hobbyists alike should rely on the ISO 216 standard dimensions — 29.7 cm × 42.0 cm — to avoid costly printing errors and to leverage the clean scaling property of the A‑series.

Related reading: 12 Inches in CM: Exact 30.48 cm Conversion Guide · 1 Tbsp Butter in Grams – Complete Baking Conversion Guide

Additional sources

snap.com.au, youtube.com, en.wikipedia.org

For a quick reference, you can also check out Our detailed guide to A3 dimensions for the exact numbers and comparisons.

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Frequently Asked Questions

What is A3 paper used for?

A3 is commonly used for posters, diagrams, architectural drawings, and large‑format layouts. Its size provides ample space for detailed information while remaining manageable for handling and display.

Is A3 the same as ledger or tabloid?

No. A3 (297 × 420 mm) is slightly taller and narrower than US tabloid/ledger size (279 × 432 mm). They are not interchangeable without adjustments.

Can I print A3 on a standard printer?

Most home printers accept only A4 or letter size. To print A3, you need a printer that supports the larger format — either a dedicated A3 inkjet or a professional office multifunction device.

What is the difference between A3 and A3+?

A3+ is slightly larger than standard A3 (typically 329 × 483 mm) to allow for bleed in printing. Use A3+ if your design extends to the edges and requires trimming.

How do I set up an A3 document in Word?

Go to Layout → Size → More Paper Sizes, then enter 29.7 cm for width and 42.0 cm for height. Ensure your printer supports A3 before attempting to print.

What is the weight of A3 paper?

A3 paper weight varies by type: standard copy paper is around 80–100 gsm, while heavier card stock for invitations or business cards can reach 250–350 gsm.

Is A3 paper size the same in all countries?

Yes, A3 is defined by the international ISO 216 standard and is the same size in all countries that use the A‑series. North America primarily uses US Letter and Tabloid, but A3 is available for import or special orders.