Paper sizesPS-08
What Is A3 Size in cm? How It Relates to A4 (2x Area, 141%), Pixels by dpi, A3 vs B4, and Printing on a Home Printer
A3 size is two A4 sheets side by side. The dimensions and pixel counts come first in a table, followed by how it differs from A4 and B4 and how to print it on a home printer.
In this article (12 sections)
- Conclusion: what is A3 size in cm, and in pixels?
- How do you get A3 size with the calculator tool?
How does A3 size relate to A4?2
How does the pixel count of A3 size change with dpi?1
- How is A3 size different from B4?
- Where is A3 size used?
What if your home printer cannot print A3 size?3
- What are common mistakes with A3 size?
- What terms come up with A3 size?
- Sources
A3 size is an A-series paper size defined by ISO 216 and JIS P 0138. It has exactly twice the area of A4.
A3 size is often used for two-page spreads, drawings and notices. Copiers can print it, but many home printers cannot.
When you make print data, decide the pixel count and the dpi as well as the size in cm.
Here is the key point. Think of A3 size as "twice A4", and the scale and pixel counts follow right away.
This article covers the following.
- A3 dimensions (mm, cm, inches) and pixel counts by dpi
- How it relates to A4 (twice the area, sides about 1.41 times) and the scale
- What dpi a phone photo gives when printed at A3
- How it differs from B4, and when to use each
- Where A3 size is used
- How to print A3 on a home printer that does not support it
The dimensions are shown in tables based on ISO 216 and JIS P 0138.
Conclusion: what is A3 size in cm, and in pixels?
| Size | A3 |
|---|---|
| Series | A |
| mm (w × h) | 297 × 420 |
| cm | 29.7 × 42 |
| inches | 11.69 × 16.54 |
| px (72 dpi) | 842 × 1191 |
| px (150 dpi) | 1754 × 2480 |
| px (300 dpi) | 3508 × 4961 |
| px (350 dpi) | 4093 × 5787 |
| Typical use | Drawings, spreads |
Source: JIS P 0138, ISO 216, ANSI/ASME Y14.1
The px values in the table are "width × height" in portrait orientation. For landscape, swap the width and height.
Choose the pixel count by how you will use it.
- Screen only (slides, viewing a PDF): the 72dpi or 150dpi values are enough
- Home printers and notices: 150 to 200dpi is a good guide
- Sending to a print shop: use 300dpi as the base, or 350dpi if they ask for it
A3 is usually viewed from a little distance. Unless it is a photo, 200dpi is easy enough to read.
The aspect ratio of A3 size is 1 : √2, the same as A4. Data made at A4 can be enlarged to A3 without changing its shape.
How do you get A3 size with the calculator tool?
To get A3 size, choose "A3" as the paper in the tool above. When you change the dpi or orientation, the pixel count changes too.
The tool also gives values not in the table, such as 96dpi or 600dpi, using the same formula. The tool runs only in your browser and does not send the values you enter.
The formula is the same as for A4. See A4 size in pixels for details.
- Width: 297 ÷ 25.4 × 300 = 3507.9 → 3508px
- Height: 420 ÷ 25.4 × 300 = 4960.6 → 4961px
How does A3 size relate to A4?
A3 size is two A4 sheets placed side by side along their long edges. The area is twice as large, and each side is about 1.41 times as long.
As the figure shows, the long side of A4 becomes the short side of A3. Two A4 sheets side by side make A3.
The scale between A4 and A3 is calculated as follows.
| Change | Width | Height | Scale |
|---|---|---|---|
| A4 → A3 (enlarge) | 297 ÷ 210 ≈ 1.414 | 420 ÷ 297 ≈ 1.414 | 141% |
| A3 → A4 (reduce) | 210 ÷ 297 ≈ 0.707 | 297 ÷ 420 ≈ 0.707 | 71% |
| Two A4 → one A3 | n/a | n/a | 100% (two pages side by side) |
This is why the "A4→A3" button on a copier is 141%. The area doubles, but the sides do not double.
What is the aspect ratio of A3 size?
The aspect ratio of A3 size is about 1.414 (√2) on the long side for 1 on the short side. You can check it with 420 ÷ 297 ≈ 1.414.
In the A series, each time you cut A0 in half, the number goes up by one. A0 has an area of about 1m², so A3 is one eighth of that.
The calculation gives 0.297 × 0.420 ≈ 0.125m². Halving does not change the ratio, so A3 and A4 have the same shape.
What happens when you fold A3 size in half?
Folding A3 size in half gives the A4 size. 420 ÷ 2 = 210, the same as the width of A4.
Folded in half, an A3 document fits A4 files and envelopes. That is why meeting materials are often printed on A3, folded and handed out.
An open A4 booklet, with two facing pages, is also A3 size. To make a spread as one sheet, set it up at A3.
How does the pixel count of A3 size change with dpi?
The pixel count of A3 size grows in proportion to the dpi. Next to A4, you can see that the height of A4 is the width of A3.
| Size | px (72 dpi) | px (150 dpi) | px (300 dpi) | px (350 dpi) |
|---|---|---|---|---|
| A3 | 842 × 1191 | 1754 × 2480 | 3508 × 4961 | 4093 × 5787 |
| A4 | 595 × 842 | 1240 × 1754 | 2480 × 3508 | 2894 × 4093 |
Source: JIS P 0138, ISO 216, ANSI/ASME Y14.1
For dpi values not in the table, we used the same formula as the tool.
| dpi | A3 in pixels (calculated) | Suited to |
|---|---|---|
| 96 | 1123 × 1587px | Viewing on screen (the CSS reference) |
| 200 | 2339 × 3307px | Documents and notices on a home printer |
| 240 | 2806 × 3969px | Printing photos large (Canon's guide) |
| 600 | 7016 × 9921px | Black-and-white line art, fine drawings |
Canon's print lessons say 240ppi is enough for a photo on A3 Nobi paper. ppi is the number of dots per inch of an image.
At 300dpi, one A3 page is about 17.4 million pixels. 3508 × 4961 is about 17.4 million, and the file gets heavy as well.
Can you print a phone photo at A3 size?
A 12-megapixel phone photo comes to about 240dpi at A3. That is a good enough guide for a photo print.
The table below gives the calculation for each pixel count. The values are for a 4:3 photo filling A3 in portrait orientation.
| Photo pixel count (example) | Pixels (4:3) | dpi at A3 (calculated) |
|---|---|---|
| 8 megapixels | 3264 × 2448 | About 197dpi |
| 12 megapixels | 4032 × 3024 | About 244dpi |
| 24 megapixels | 5712 × 4284 | About 345dpi |
| 48 megapixels | 8064 × 6048 | About 488dpi |
The calculation is the long side of the photo ÷ the long side of A3 (420 ÷ 25.4 ≈ 16.5 inches). 4032 ÷ 16.5 ≈ 244.
A photo's ratio is 4:3, a little different from the ratio of A3. If you fill A3 with it, a little is cut off at the top and bottom or at the sides.
Cropped or zoomed photos have fewer pixels. Check the pixel count in the photo's details before you print.
How is A3 size different from B4?
A3 size is a step larger than B4. A3 has about 1.33 times the area of B4.
| Size | mm (w × h) | cm |
|---|---|---|
| A3 | 297 × 420 | 29.7 × 42 |
| A4 | 210 × 297 | 21 × 29.7 |
| B4 | 257 × 364 | 25.7 × 36.4 |
Source: JIS P 0138, ISO 216, ANSI/ASME Y14.1
B4 is a paper size in the JIS B series. It sits between A3 and A4, so copiers often offer both.
| Point | A3 | B4 (JIS) |
|---|---|---|
| Standard | ISO 216 and JIS P 0138 (same size worldwide) | JIS P 0138 (different from ISO B4) |
| Area (calculated) | 297 × 420 = 124,740mm² | 257 × 364 = 93,548mm² |
| Scale to the other | A3 → B4 is 86% | B4 → A3 is 115% |
| Scale to A4 | 71% | 82% |
| Folded in half | A4 | B5 |
For each scale, we calculated the width and the height and took the smaller one. For B4 → A3, the width is 297 ÷ 257 ≈ 1.156. The height is 420 ÷ 364 ≈ 1.154.
If you choose B4 in software or print services from outside Japan, it may print at ISO B4. If you want Japanese B4, check the size in mm.
The best way to choose between A3 and B4 is whether you are matching A4. Use A3 if it goes out with A4 documents, and B4 if you are matching B5.
Where is A3 size used?
A3 size is used for materials that are too small on A4 and for notices read from a distance. The main uses are in the table below.
| Use | Why choose A3 | Tips for making it |
|---|---|---|
| Meeting materials, documents with many tables | Twice the area of A4, so a table fits on one sheet | Folded in half, it fits an A4 file |
| Spreads (booklets, brochures) | The size of an open A4 booklet | Do not put text on the center fold |
| Drawings and maps | Fine lines print without shrinking | Print at 600dpi or straight from the PDF |
| Shop notices and POP displays | Readable from a little distance | Use large text and keep to the key points |
| School and community notices | Easy to put up on a notice board | The board's frame hides the edges |
| Photo prints | Display larger than A4 | 12 megapixels gives about 240dpi |
For larger notices, choose from A2 or B2. See poster sizes for how to choose.
Among notices you can make at home, A3 is close to the largest size that is still easy to handle. Anything larger than A2 has to be printed in parts at home.
What if your home printer cannot print A3 size?
If your home printer does not support A3, shrink the page to A4 or print it across two A4 sheets. If you need one full-size sheet, you can also print at a convenience store.
| Method | Result | Suited to | Where to set it |
|---|---|---|---|
| Shrink to A4 | 71% of A3 size | Checking the content, reading at hand | The printer's "Output Paper Size", or "Shrink oversized pages" for a PDF |
| Print across two A4 sheets | Taped together, the size of A3 | Seeing notices or drawings at full size | Canon's "Poster (1 × 2)", Acrobat's "Poster" |
| Use a convenience store copier | One A3 sheet | When you need only one or a few sheets | Register a PDF with Netprint and print it |
| Use a printer that supports A3 | A3 or A3 Nobi | Printing A3 often | Choose A3 as the paper size in the driver |
Shrink to A4 first to check, then print only the final version on A3. You waste neither paper nor ink.
How much smaller does text get when you shrink A3 size to A4?
When you shrink A3 size to A4, text also becomes about 71% of its size. 10.5pt text becomes about 7.4pt.
| Text size on A3 | Size after shrinking to A4 (calculated) |
|---|---|
| 10.5pt | About 7.4pt |
| 12pt | About 8.5pt |
| 14pt | About 9.9pt |
| 18pt | About 12.7pt |
The calculation is 10.5 × 0.707 ≈ 7.4.
If the page will be shrunk to A4, setting the A3 body text at 14pt or larger keeps it easy to read. Decide before you start whether you will hand it out shrunk or at full size.
In the Canon driver, choose A3 as the "Page Size". When you choose A4 as the "Output Paper Size", the scale is set automatically. The application's settings may take priority.
How do you print A3 size across two A4 sheets?
To split A3 size across two A4 sheets, use the printer's poster printing (tiled printing). On Canon, choose "Poster (1 × 2)" under "Page Layout".
The Canon driver can also add cut lines and marks for trimming and for the paste margin.
For a PDF, you can also split it in Acrobat's print dialog. Under "Page Size & Handling", choose "Poster".
Paper has an unprintable margin at the edges. So the taped-together result is slightly smaller than A3.
Tape the sheets from the back and the seam is hard to see. Line up the paste margin marks before taping, and the sheets are less likely to shift.
How is A3 Nobi different from A3 size?
A3 Nobi is a photo paper size a step larger than A3. Epson's paper list gives it as 329 × 483mm.
It is 329 − 297 = 32mm wider than A3. It is 483 − 420 = 63mm taller.
On A3 Nobi, you can place margins and crop marks (marks for trimming) outside the finished A3 area. A3 Nobi is not an ISO or JIS standard but a size name used by printer makers.
What are common mistakes with A3 size?
The most common one is printing A3 data with the paper setting still on A4. Mistakes people often ask about are in the table below.
| Mistake | What happens | Fix |
|---|---|---|
| Printing A3 data with the paper set to A4 | The lower right is cut off, or it is shrunk without meaning to | Match the paper size in both the application and the printer |
| Enlarging A4 at 200% | It runs off the A3 sheet | Enlarge at 141% |
| Stretching a 72dpi image to A3 | It looks blurry | Make sure it is 150dpi or more |
| Choosing B4 in software from outside Japan | It becomes ISO B4, a different size | Check the size in mm |
| Setting body text at 10.5pt when it will be shrunk | At A4 it is about 7.4pt and hard to read | Set the body text at 14pt or more |
| Putting text on the center fold of a spread | It cannot be read when folded in half | Leave a margin in the middle |
| Mailing A3 unfolded in an envelope | The long side is over 34cm, so it is non-standard (oversize) | Fold it in half and send it in a Kaku 2 |
Checking that the paper size in the application matches the paper size in the printer prevents almost all of these.
What terms come up with A3 size?
| Term | Meaning | Source |
|---|---|---|
| A series | Paper sizes made by cutting A0 in half | ISO 216, JIS P 0138 |
| B series | Sizes between the A sizes. ISO and JIS sizes differ | ISO 216, JIS P 0138 |
| Trimmed size | The size of paper after it is cut and finished | JIS P 0138 |
| dpi | Dots per inch. How fine the print is | Printer makers' terms |
| ppi | Pixels per inch of an image | Canon's print lessons |
| Scale | The enlargement or reduction ratio. Use the smaller of width and height | Calculation |
| Poster printing | A feature that prints one page across several sheets | Canon and Adobe manuals |
| A3 Nobi | A photo paper size a step larger than A3 | Epson's paper list |
| Crop marks (tombo) | Marks showing where to cut | General printing term |
What else should you know about A3 size?
How do you mail an A3 document?
An A3 document is usually folded in half and sent in a Kakugata No. 2 envelope (Kaku 2) or a Kaku A4. Folded in half, it is the size of A4.
If you put A3 in an envelope without folding, the long side is over 34cm. In Japan Post's rate table, it falls in the non-standard (oversize) class.
To send it unfolded, sandwich it between cardboard and send it at the oversize rate. Check the postage in Japan Post's rate table.
What if you want to print larger than A3 size?
To print larger than A3 size, choose A2 or A1, or B3 or B2. In the A series, each step up makes the sides about 1.41 times longer.
The size of a notice depends on how far away people will view it. See poster sizes for how to choose.
Where can you see paper dimensions all together?
You can see the A and B series together in the paper size list.
US Tabloid is close to A3 but a different size. For how US paper differs, see the comparison in Letter size vs A4.
Where do this site's figures come from?
The dimensions on this site come from a single dataset based on ISO and JIS documents. The tables and the tool read the same data.
How we check figures and our editorial policy are described in About this site.
ConversionsHow many pixels is A4? A chart by dpi, how the calculation works, and how to make print dataA4 pixel counts at 72, 150, 300 and 350 dpi, how to calculate them, the dpi each use needs, Word, PowerPoint and Photoshop settings, phone photos, and common mistakes.
Paper sizesPaper Size Chart: A, B, Letter, Photo and Postcard Sizes, Uses, How to Choose and ScalingPaper sizes in mm, cm and inches with uses. A and B series rules, ISO vs JIS B sizes, Letter, photo, postcard and business card sizes, choosing by use and scaling.
Paper sizesPoster Size List: A0 to B3 Dimensions and How to Choose by Use, Viewing Distance and ResolutionPoster sizes A0 to A3 and B0 to B3 in mm, cm and pixels, how to choose for shops, stations, events, rooms and conferences, text size, dpi, frames and tiled printing.Frequently asked questions about A3 size
What is A3 size in cm?
It is in the cm row of the conclusion table. It is the size of two A4 sheets side by side.
The aspect ratio is 1 : √2, the same as A4.
How many times bigger than A4 is A3?
Twice the area. Each side is about 1.41 times longer, so the copier scale is 141%.
To shrink A3 to A4, use 71%.
How many pixels is A3 size?
It depends on the dpi. At 300dpi, the standard for print, it is 3508 × 4961px.
At 350dpi, it is 4093 × 5787px.
Which is bigger, A3 or B4?
A3 is bigger. A3 has about 1.33 times the area of B4.
To enlarge B4 to A3, the scale is 115%.
How do you print A3 on a home printer?
If the printer does not support A3, shrink the page to A4 or print it across two A4 sheets.
If you need one full-size sheet, you can also print it on a convenience store copier.
Sources
- ISO 216:2007 Writing paper and certain classes of printed matter. Trimmed sizes. A and B series (ISO)
- JIS P 0138 Trimmed sizes of processed paper (Japanese Industrial Standards Committee, JIS search; in Japanese. Finished sizes of the A and B series)
- CSS Values and Units Module Level 3: Absolute lengths (W3C)
- Print lessons that change your photos, Lesson 3: Pixel count and resolution (Canon, in Japanese. Resolution needed for photo prints)
- Printing enlarged or reduced (Canon online manual, in Japanese. Page Size and Output Paper Size settings)
- Poster printing (Canon online manual, in Japanese. Splitting one page across several sheets)
- Print large documents as posters in Acrobat (Adobe, in Japanese. The Poster option in the print dialog)
- Fixing PDF print size problems (Adobe, in Japanese. Shrinking oversized pages)
- Colorio printer photo print paper list (Epson, in Japanese. A3 Nobi dimensions)
- Netprint specifications (Fujifilm Business Innovation, in Japanese. Printable paper sizes)
- Domestic rate table (letters and postcards) (Japan Post, in Japanese. Size limits for standard-size and non-standard-size mail)
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