How Big is A3 Paper? Size in mm, cm, Inches & A4 Comparison

If you’ve ever stood in a stationery aisle trying to picture exactly how big a sheet of A3 paper really is, you’re not alone. It’s a common point of confusion, especially when you need to know whether it’ll fit your project or printer. This article breaks down the exact dimensions of A3 in every unit you’ll encounter, shows how it stacks up against A4 and the rest of the A-series family, and explains what all of this means for your printing or design work.

Dimensions (mm): 297 × 420 ·
Dimensions (inches): 11.69 × 16.54 ·
Area: 0.125 m² ·
Compared to A4: Twice the size ·
ISO Standard: A-series (ISO 216)

How big is an A3 size?

A3 is an internationally standardized paper size that measures exactly 297 mm × 420 mm (29.7 cm × 42 cm), according to the Adobe Creative Cloud guide to international paper formats. In imperial measurements, that’s 11.69 inches × 16.54 inches.

A3 size in mm and cm

The metric system makes this straightforward: A3 is 297 millimeters wide and 420 millimeters tall. Converting to centimeters gives you 29.7 cm × 42 cm — measurements you’ll often see on European packaging and office supplies. This precision comes from the Neenah Paper resource on international sizes, which explains that the ISO 216 standard defines these exact proportions.

A3 size in inches

In inches, A3 measures 11.69 × 16.54 inches, as documented by Paper Sizes Wiki. Some sources round this to 11.7 × 16.5 inches for simplicity, but the precise figure is more useful for accurate printing work. The difference matters when you’re working with tight margins or precise crop marks.

A3 printing surface area

The total printing surface area of A3 is 0.125 square meters (1,250 cm²), according to Adobe Creative Cloud. This is exactly twice the area of A4, which makes sense given the mathematical relationship between A-series sizes — each size in the series is precisely half the area of the size above it.

How bigger is A3 than A4?

A3 is exactly twice the size of A4. Not roughly — the dimensions are mathematically precise: A4 measures 210 mm × 297 mm (VC Print), and doubling that gives you 297 mm × 420 mm. The relationship works in reverse too: cutting an A3 sheet in half produces two A4 sheets.

Direct size comparison

• A3: 297 × 420 mm (11.69 × 16.54 inches)
• A4: 210 × 297 mm (8.27 × 11.69 inches)
• A3 is exactly double A4 in area
• A3 folded once equals A4 in size

A3 vs A4 dimensions

The width of A3 (297 mm) matches the height of A4 (297 mm), while A3’s height (420 mm) is double A4’s width (210 mm). This symmetry is intentional — it’s what makes the A-series so useful for scaling and folding. When you fold an A3 sheet in half along its shorter edge, it becomes exactly A4-sized. Papersizes.io confirms that cutting A3 in half creates two A4 sheets.

What is A1, A2, A3, and A4?

The A-series is a family of paper sizes defined by ISO 216, where each size halves the previous one when cut. Formax Printing explains that all A-series sizes share a uniform aspect ratio of 1:√2 (approximately 1:1.414), which allows consistent scaling regardless of which size you’re using.

A-series overview

At the top of the series, A0 is defined as exactly one square meter of surface area. Each subsequent size (A1, A2, A3, A4, and so on) is created by halving the preceding size. This means A1 is half of A0, A2 is half of A1, and A3 is half of A2.

The mathematical elegance of the A-series means each size step represents a precise halving or doubling. A3 at 297 × 420 mm sits comfortably in the middle of this family, making it versatile enough for posters, architectural drawings, and professional documents while remaining compatible with standard office equipment.

Is A3 folded in half A4?

Yes — and this is one of the most practical features of the A-series. Folding an A3 sheet exactly in half along its 297 mm edge produces a sheet that measures 210 mm × 297 mm, which is precisely A4 size.

Folding relationship

The geometry works because A3’s 297 mm width equals A4’s height, and A3’s 420 mm height is exactly double A4’s 210 mm width. This means no paper is wasted when folding, and the resulting sheet has the same proportions as the original. As Papersizes.io confirms, cutting A3 in half produces two perfect A4 sheets.

Practical uses

This folding relationship makes A3 ideal for brochures and bound documents. A single A3 sheet folded once creates a 4-page A4 booklet (front, back, inside-left, inside-right). G. Flesch’s comparison guide notes that A3 printers can accommodate ledger-size (11 × 17 inch) paper, which is the US equivalent of A3.

What size is A3 in pixels?

Pixel dimensions depend entirely on the resolution (DPI or PPI) you’re working with. Higher resolution means more pixels. Paper Sizes Wiki and Formax Printing provide figures for common screen and print resolutions.

Common resolutions

The implication: lower resolutions suit digital screens, while print work demands the higher 300 PPI setting for crisp, professional results.

300 DPI equivalent

For professional print work, you’ll want 300 PPI minimum. At that resolution, an A3 image measures 3,508 × 4,961 pixels — that’s over 17 million pixels total. This is the standard resolution for magazines, high-quality brochures, and any print work that will be viewed up close.

Quotes

The most common international paper size is A4, which measures 8-1/4 × 11-3/4 inches or 210 × 297 mm.

— Neenah Paper (paper manufacturer and industry resource)

Paper measurements are defined by the ISO 216 standard, which ensures consistent dimensions across all participating countries.

— Neenah Paper (paper manufacturer and industry resource)

The uniform aspect ratio of 1:√2 is maintained across all A-series sizes, allowing any size to be scaled to any other while preserving proportions.

— Formax Printing (commercial printing resource)

Summary

A3 paper is exactly 297 × 420 mm (11.69 × 16.54 inches) with a surface area of 0.125 m² — precisely twice the size of the more common A4. The ISO 216 standard that defines these dimensions has remained consistent globally since 1975, making A3 a reliable choice for anyone working across international markets. For print buyers and designers, the practical takeaway is clear: A3 serves as the workhorse size for posters, architectural drawings, and folded brochures, while its pixel dimensions at 300 DPI (3,508 × 4,961) tell you exactly what resolution you need for professional-quality output.

Related reading: 163 cm in Feet and Inches · Size 6 UK in EU

As UK Vantage analysis explains, A3’s 297 × 420 mm dimensions double A4’s area while bridging everyday printer paper and broadsheet formats.

Frequently asked questions