Paper Sizes and Pixel Counts

Gives the dimensions of A and B series paper and works out the pixel count at a resolution you choose. An A4 page at 350 dpi is 2894 by 4093 pixels, the figure needed when preparing artwork for print.

This gives the dimensions of A and B series paper and works out the pixel count for print artwork.

\text{pixels} = \dfrac{\text{mm}}{25.4} \times \text{dpi}

dpi counts dots per inch, so the millimetres are divided by 25.4 to give inches before multiplying.

Folding in half gives the next size down

Folding either series in half across the long side produces the next size down. This works because the aspect ratio is 1 to √2: after folding, the long side becomes the short side and half the long side becomes the new long side, and since $\sqrt{2} \div 2 = 1 \div \sqrt{2}$ the ratio survives. A0 is defined to have an area of one square metre, and A4 is a sixteenth of it.

Example

A4 is 210 by 297 mm. At 350 dpi that is $210 \div 25.4 \times 350 = 2894$ pixels across and 4093 down, some 11.85 megapixels in all. At 300 dpi it comes to 2480 by 3508, a size widely used in print.

Notes

The standards fix the dimensions in whole millimetres, so the real aspect ratios are not exactly √2 = 1.4142. A5 works out at 210 ÷ 148 = 1.4189, slightly off. The area ratios are likewise not exactly 2.

The B series here follows the Japanese standard. The ISO B series has different dimensions, so check which is meant when working across borders.