A3 is the paper size that sits one step above A4 and is used for posters, large format prints, technical drawings and presentation printouts that need more space than a standard A4 page provides. The pixel dimensions of an A3 image depend on the resolution it is being prepared for. At 72 DPI for screen display an A3 image is 842x1191 pixels in portrait orientation. At 150 DPI for general print use it is 1754x2480 pixels. At 300 DPI for high quality print output it is 3508x4961 pixels. Getting the right pixel count for the intended output resolution is what makes the difference between a print that looks sharp and one that looks soft.
How to Resize an Image to A3
For A3 at 300 DPI, enter 3508 in the width field and 4961 in the height field for portrait orientation, or swap the values for landscape. For A3 at 150 DPI, enter 1754 in the width field and 2480 in the height field. For A3 at 72 DPI screen resolution, enter 842 in the width field and 1191 in the height field.
If the original image is already close to an A3 aspect ratio, leaving the Maintain Aspect Ratio checkbox on scales cleanly. If the original is a different ratio, turn it off to force the exact A3 dimensions. Be aware that forcing a very different aspect ratio into A3 dimensions will distort the image. For print work, using an image that is already close to A3 proportions gives the cleanest result. Upload multiple images at once and download as a ZIP when done.
A3 Pixel Dimensions Reference
A3 portrait at 72 DPI: 842x1191 pixels. A3 portrait at 150 DPI: 1754x2480 pixels. A3 portrait at 300 DPI: 3508x4961 pixels. A3 landscape at 300 DPI: 4961x3508 pixels. For most professional print use, 300 DPI is the standard. For general purpose printing where file size needs to stay manageable, 150 DPI gives acceptable results for most print services.
Output Format for A3 Print Images
JPEG is the practical choice for photographic A3 prints where managing file size is a concern. At 300 DPI an A3 PNG can be very large and JPEG keeps the file to a more manageable size without noticeable quality loss for photographic content. PNG is worth using for illustrated posters, text heavy designs and anything with flat colors or transparent areas where lossless quality matters more than file size. Most print services accept both formats.