Quick answer: A3 paper is 297 × 420 millimetres, or 29.7 × 42 centimetres and approximately 11.69 × 16.54 inches. It has the ISO A-series aspect ratio of 1:√2, so it can be enlarged or reduced to neighbouring A sizes without changing the page shape.
A3 is exactly twice the area of A4. It is the largest format supported by many office multifunction printers and a useful bridge between document and poster work.
Measurement note: dimensions are stated width × height in portrait orientation. Turn the sheet through 90 degrees for landscape use. Millimetres are the controlling values for ISO sizes; inch figures are rounded conversions.
A3 dimensions
| Unit | Width | Height |
|---|---|---|
| Millimetres | 297 mm | 420 mm |
| Centimetres | 29.7 cm | 42 cm |
| Inches | 11.69 in | 16.54 in |
| Area | 124,740 mm² | 0.1247 m² |
For A3, the stated size is the finished, trimmed sheet. It does not include printer bleed, crop marks, binding allowance or the non-printable border imposed by a particular machine. For a general comparison, see the complete paper size chart and the explanation of ISO 216 paper sizes.
What is A3 paper used for?
A3 is commonly chosen when the reader needs a page that is easy to handle while preserving the familiar A-series proportions. Typical uses include:
- Small posters
- Folded brochures made down to a4
- Spreads and proof sheets
- Drawings, menus and classroom handouts
Whether A3 is the right choice still depends on viewing distance, amount of information, type size, folding, finishing and the printer available. A format can be technically large enough but still feel crowded if the design has no clear hierarchy or if essential text is placed too close to the trim.
How A3 relates to other A sizes
- Two A3 sheets placed side by side along their long edges form one A2 sheet in area.
- Cutting A3 in half parallel to its short edge produces two A4 sheets.
- Relative to A4, A3 has 2 times the area of A4.
- Because every A size has the same 1:√2 aspect ratio, a layout can be scaled proportionally between A sizes without cropping. Type and line weights must still be checked because a mathematically scaled design may become too small or too heavy in practice.
Printing on A3 paper
Many office printers support this size, but borderless printing, duplexing and tray capacity vary by model.
- Set the document page to exactly 297 × 420 mm for a finished A3 page.
- Use PDF for final artwork unless the printer asks for another format; embed fonts and keep placed images at an effective resolution suitable for the viewing distance.
- Add the printer’s requested bleed. A common commercial value is 3 mm on every edge, but the correct figure is the one in the supplier’s specification.
- Keep text, logos and critical marks inside a safe area. Ten millimetres is a useful starting point for many general jobs, although binding and large-format finishing can require more.
- Print or view a 100% scale proof and verify one known measurement before authorising the full run.
Page size with 3 mm bleed
With 3 mm bleed on all four sides, the artwork canvas becomes 303 × 426 mm. The final product is still trimmed back to 297 × 420 mm. Do not enlarge the finished dimensions themselves to create bleed; extend background images and colours beyond the trim line.
Choosing weight and finish
For everyday documents, 80–100 gsm is common. Reports, covers and premium handouts often use 120–250 gsm depending on printer limits and finishing.
For a A3 job, uncoated paper is easy to write on and usually gives a natural, low-glare surface. Coated stocks reproduce photographs and solid colour more sharply but may crack on folds unless the grain direction and scoring are handled correctly. Always confirm the machine’s supported paper range before buying a full pack.
Is A3 the right size?
Choose A3 when its finished dimensions match the way the piece will be read, carried, displayed or mailed. If the content feels crowded, move up to A2; if there is excessive empty space or portability matters more, test A4. A physical dummy is more reliable than judging scale only on a monitor.
Frequently asked questions
What is A3 in inches?
A3 is approximately 11.69 × 16.54 inches. These are rounded conversions; use 297 × 420 mm for accurate setup and production.
What aspect ratio is A3?
A3 has the 1:√2 aspect ratio, approximately 1:1.414. This is shared by all ISO A-series sizes.
How many A4 sheets fit in A3?
Two A4 sheets have the same nominal area as one A3 sheet. Four sheets of A5 would fit if that size exists and cutting loss is ignored.
Sources and standards
The measurements and production guidance in this guide were checked against the following standards bodies, postal operators and print-platform specifications. Standards can be revised or withdrawn, so check the linked record when a contractual or regulated specification matters.