Work out poster scaling instantly with clear inputs, formula shown and shareable results.
Scaling multiplies both dimensions by the same factor, and because the pixel count is unchanged the effective resolution falls in inverse proportion to that factor. Posters are viewed from further away, so 150 dpi is usually enough, which is why an A3 file can be enlarged to A1 without visible loss.
Target height
height = original height x target width / original width
Effective resolution
new dpi = original dpi / scale factor
height = original height x target width / original width. Scaling multiplies both dimensions by the same factor, and because the pixel count is unchanged the effective resolution falls in inverse proportion to that factor.
Posters are viewed from further away, so 150 dpi is usually enough, which is why an A3 file can be enlarged to A1 without visible loss.
Enter original width, original height, target width, original file resolution. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.