A PrintScale guide
What resolution do I need for an A3 poster?
A3 is 29.7 × 42.0 cm: a useful size for artwork, smaller posters and photographic prints viewed up close.
By PrintScale · Updated
Use the actual paper dimensions
A3 is 297 × 420 mm. Calculate each pixel edge with centimetres ÷ 2.54 × PPI, rounded to the nearest whole number. Do not substitute the rounded description of A3 in inches if you need to match the millimetre dimensions precisely.
Printers may request additional bleed, which increases the artwork dimensions. A border is different: it reduces the image area inside the same sheet. Ask which size the printer expects for the image itself.
Make the crop before the enlargement
A typical phone photo is 4:3 and a typical camera photo is 3:2; neither exactly matches the A-series paper proportion. Decide whether to crop or keep a border before choosing a pixel target. A crop removes pixels, so calculate using the dimensions of the cropped source.
PrintScale preserves the uploaded image's proportions when setting its long edge. For an A3 crop, the long edge is 42 cm. A rectangular target label does not change the shape of an uncropped photo.
A3 pixel reference table
| Image density | Paper size, cm | Required pixels | Approximate megapixels |
|---|---|---|---|
| 150 PPI | 29.7 × 42.0 | 1,754 × 2,480 | 4.3 |
| 300 PPI | 29.7 × 42.0 | 3,508 × 4,961 | 17.4 |
| 600 PPI | 29.7 × 42.0 | 7,016 × 9,921 | 69.6 |
All figures exclude bleed. PPI measures the image pixels allocated to an inch of print; the DPI label used by print tools is often shorthand for that image density.
Check a small proof
Inspect the original at full pixel scale for focus, then inspect the enlargement for invented detail or sharpening halos. A physical crop printed at the intended scale lets you judge detail without paying for the whole poster. Use the paper and printer you intend to use for the final result.
Compare your source in the print-size calculator, or read Adobe's print-resolution guidance.
If the source needs enlarging, check a supported print size in PrintScale.