A3 is 297 × 420 mm — twice the area of A4, and the size most posters, plots and mounted artboards are printed at. Here it is in pixels at every common DPI.
A3 in pixels, by DPI
A3 paper is 297 × 420 mm (11.69 × 16.54 in). Nothing about that changes; the pixel count does, because it scales with the resolution you export at. These are the dimensions at the DPIs you are most likely to need for a poster, a plotted drawing or a presentation board:
DPI
Pixels (px)
72
842 × 1191 px
96
1123 × 1587 px
150
1754 × 2480 px
300
3508 × 4961 px
600
7016 × 9921 px
For comparison at 300 DPI: A2 (420 × 594 mm) is 4961 × 7016 px, A4 (210 × 297 mm) is 2480 × 3508 px, and Tabloid (11 × 17 in) is 3300 × 5100 px.
Unit converter
DPI
Paper size
Portrait / Landscape
Size (mm)210.00 × 297.00 mm
Size at 300 DPI (px)2480 × 3508 px
Bleed & safe margin
Trim size210.00 × 297.00 mm · 2480 × 3508 px
With bleed216.00 × 303.00 mm · 2551 × 3579 px
Safe area204.00 × 291.00 mm · 2409 × 3437 px
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Setting up an A3 poster or drawing
1
Start from the A3 preset
Choose A3 in the paper size preset and set your DPI. Millimeters, centimeters, inches and pixels stay linked, so editing any one of them updates the rest — handy when the printer quotes millimeters and your artboard is in pixels.
2
Flip to landscape for wide layouts
Landscape gives you 420 × 297 mm — the orientation wall charts, timelines and floor plans usually run in, and the same shape you get by butting two portrait A4 sheets together. Both pixel sizes are shown as you toggle.
3
Add bleed for a large-format print
Enter your bleed and safe margin in millimeters to see trim size, size with bleed and safe area together, in mm and px, before you set up the canvas. Large-format shops trim off the roll, so 3 mm of bleed on all four sides is the usual minimum. Large-format work is also where the DPI question gets asked most often, and our 300 DPI explainer explains what the number in the file does and does not promise.
4
Compare against A2 or A4
Switching the preset to the size above or below gives the same breakdown. Because every A size shares the 1:√2 ratio, the step between them is a clean 141 % up or 71 % down — the quickest way to check whether existing artwork can be reused.
Where the A3 pixel size actually gets used
A3 sits on the boundary between desktop printing and large format, and each side of that boundary wants a different number. These are the four jobs that send people looking for an A3 pixel size, with the arithmetic already done.
A poster going to a large-format printer
The artboard starts at 3508 × 4961 px for 300 DPI. Add the usual 3 mm bleed on all four sides and the sheet becomes 303 × 426 mm, or 3579 × 5031 px — note that the same 3 mm adds 71 px to the width and only 70 px to the height, because 297 mm and 420 mm round to whole pixels differently. Keep headlines and logos at least 5 mm (59 px) inside the trim line; a roll-fed cutter drifts more than a guillotine does. For any other bleed figure, the mm to px converter does the conversion.
A technical drawing sent to a plotter
Drawing sheets are not the full paper size. The ISO 5457 frame leaves a 20 mm filing margin on the binding edge and 10 mm on the other three, so the drawable area of an A3 sheet is 267 × 400 mm — 3154 × 4724 px at 300 DPI. Line work is where 600 DPI genuinely earns its place: hairlines and dimension arrows survive the extra sampling, at the cost of a 7016 × 9921 px file. To check that a raster detail will land at the right physical size on the plot, the px to mm converter runs the maths in reverse.
Printing A3 artwork on an A4 printer
Two routes, and they give different results. Scaling fits the whole sheet at 71 % (1 ÷ √2), the reduction a photocopier labels A3→A4 — the layout survives intact, but a 6 pt caption ends up at 4.2 pt. Tiling keeps the size and splits the image across two A4 sheets, which is what you want for a proof of a large piece; the image splitter cuts an A3-sized export into equal halves. Going the other way, blowing a 2480 px wide A4 image up to A3 width spreads it across 297 mm at just 212 DPI, so start from A3 rather than enlarging.
A3 versus Tabloid on a US job
They are close enough to be mistaken for each other and different enough to ruin a layout. A3 is 297 × 420 mm; Tabloid (Ledger) is 11 × 17 in, which is 279.4 × 431.8 mm. At 300 DPI that is 3508 × 4961 px against 3300 × 5100 px, so A3 artwork dropped onto Tabloid at full size loses 208 px off the width while leaving 139 px of empty height at the foot. Neither crops cleanly into the other. If the job is heading to a North American shop, our US Letter page covers the sizes they will quote in.
Choosing a DPI for an A3 file
Every row describes the same 297 × 420 mm sheet sampled at a different resolution. On a format this large the file size climbs fast, so pick the row that matches the viewing distance rather than the biggest number in the list.
DPI
A3 in pixels
Best for
Watch out for
72
842 × 1191 px
Point-based layout files and PDF page boxes.
This is the figure a PDF reports for an A3 page, because the format measures in 72-per-inch points. It is a unit, not a print resolution.
96
1123 × 1587 px
Screen mockups of a poster, slide-embedded previews, web PDFs.
The CSS reference resolution. Perfectly sharp on a display, obviously soft the moment it goes on a wall.
150
1754 × 2480 px
Posters read from a metre or more, plotted drafts, event backdrops.
Half the linear resolution of a 300 DPI export and a quarter of the pixels. Fine at viewing distance, rough if anyone walks up to it.
Around 17.4 megapixels — twice an A4 page at the same DPI, and it doubles again for every step up the A series.
600
7016 × 9921 px
CAD line work, hairline rules, scanned drawings headed for vectorisation.
About 69.6 megapixels, roughly 209 MB as uncompressed 8-bit RGB. Most editors get slow at this size, and a press cannot resolve it on continuous-tone art anyway.
Pixel figures round 297 × 420 mm to the nearest whole pixel, which is exactly why 3 mm of bleed adds 71 px across the width and 70 px down the height instead of the same number twice.
Frequently asked questions
How many pixels is A3 at 300 DPI?
A3 at 300 DPI is 3508 × 4961 px in portrait, or 4961 × 3508 px in landscape. That is the resolution commercial printers ask for, and it is what you want any raster element in a poster to be sized at before you place it.
Is A3 exactly double A4?
In area, yes. A3 is 297 × 420 mm and A4 is 210 × 297 mm, so the long edge of A4 becomes the short edge of A3 — put two A4 sheets side by side in landscape and you get an A3. The proportions stay identical, which is why scaling artwork between the two never leaves empty strips.
Do I really need 300 DPI for an A3 poster?
Not always. A poster read from a meter or two away holds up fine at 150 DPI, which is 1754 × 2480 px for A3 and roughly a quarter of the file size. Reserve 300 DPI for pieces that get held in the hand or inspected up close, such as exhibition panels or portfolio prints.
What size should I use for an A3 mockup on screen?
At 96 DPI — the reference resolution browsers and most UI tools use — A3 is 1123 × 1587 px. That is the right canvas for a poster preview that will only ever be viewed on a display or shared as a screen PDF.
Can a normal desktop printer output A3?
Most home and office printers top out at A4, so an A3 file sent to one gets scaled down to fit or split across sheets. For a full-size A3 you need an A3-capable printer or a print shop — worth confirming before you commit to the larger canvas.
My A3 export has the right pixel count but still looks soft. Why?
Pixel dimensions alone do not create detail. Enlarging a photo that was originally, say, 1200 px wide up to 3508 px only spreads the existing pixels further apart, so the image goes soft even though the file now measures A3. Start from a source large enough for the final size, or use vector artwork, which has no fixed pixel count at all.
What enlargement percentage takes A4 artwork up to A3?
141 %, and 71 % brings it back down — those are the two buttons on a photocopier, and they come from the 1:√2 ratio the whole A series is built on. The catch is resolution rather than geometry: a 2480 px wide A4 image enlarged to A3 width now spans 297 mm, which works out to about 212 DPI. The layout survives the enlargement; the raster detail does not.
Is A3 the same as Tabloid or Ledger paper?
No. A3 is 297 × 420 mm, while Tabloid (also called Ledger) is 11 × 17 in — 279.4 × 431.8 mm. A3 is 17.6 mm wider and 11.8 mm shorter, so at 300 DPI you are comparing 3508 × 4961 px with 3300 × 5100 px. Placed on Tabloid at full size, an A3 layout loses 208 px of width and leaves 139 px of unused height, and neither sheet crops cleanly into the other.
How much of an A3 technical drawing is actually drawable?
Less than the sheet. The ISO 5457 drawing frame keeps a 20 mm filing margin on the binding edge and 10 mm on the remaining three, which leaves 267 × 400 mm inside the border — 3154 × 4724 px at 300 DPI. Title blocks eat into that further, so size the drawing area from the frame rather than from the 297 × 420 mm sheet.
How big is an A3 file compared with the same design at A4?
Twice as many pixels, because A3 is exactly twice the area. At 300 DPI, A4 is 2480 × 3508 px (about 8.7 megapixels) and A3 is 3508 × 4961 px (about 17.4 megapixels). Held uncompressed as 8-bit RGB, the A3 page is roughly 52 MB in memory against 26 MB for A4. Compressed on disk both land far below that, but the ratio between them stays the same.
What is A3 in pixels at 600 DPI, and is it ever worth it?
A3 at 600 DPI is 7016 × 9921 px, about 69.6 megapixels. It is worth it for line art, CAD plots, engraved detail and scans of small type, where hard edges gain from the extra sampling. It is wasted on photographs: presses cannot resolve much beyond 300 DPI of continuous tone, so you get a file four times heavier for detail that never reaches the paper.