Pixels to Inches Calculator

The conversion needs a resolution

Pixels do not have a physical size, so converting them to inches requires a resolution to divide by. Pixels divided by pixels per inch gives inches.

Three thousand pixels at 300 PPI is 10 inches. The same 3000 pixels at 150 PPI is 20 inches. Both are correct and they describe different prints from the same file.

Which is why the question of how big an image is cannot be answered without asking how sharp it needs to be. The two are traded against each other and the answer depends on the use.

The 96 convention on screens

For screen work, CSS defines one inch as 96 pixels. It is a convention rather than a measurement, and it does not correspond to any particular display.

It exists because layouts need a consistent unit, and it is why a CSS inch is not an inch on your monitor. A 1920 pixel wide window is 20 CSS inches regardless of whether the monitor is 22 inches or 34.

For print work this convention is irrelevant and actively misleading. Print resolution comes from the intended physical size, and applying 96 to a print job produces something at roughly a third of the resolution it needs.

Working out whether an image is big enough

The practical question is usually the reverse: given this file, how large can it print acceptably. Pixel dimensions divided by the required resolution gives the maximum size.

A 4000 by 3000 pixel photograph at 300 DPI prints at 13.3 by 10 inches. At 200 DPI, which is perfectly adequate for a wall print viewed from a metre, it prints at 20 by 15.

Stating both figures when advising someone is more useful than a single answer, because it makes the trade visible. Many people asked whether their photo is big enough for a poster assume the answer is binary when it is a matter of how close anyone will stand.

Millimetres, and where they are standard

Most of the world specifies print in millimetres rather than inches, and print suppliers outside the US almost universally do.

The conversion is 25.4 millimetres to the inch, so a resolution of 300 DPI is roughly 11.8 pixels per millimetre. An A4 page at 210 by 297 millimetres needs 2480 by 3508 pixels at 300 DPI.

Those A-series pixel dimensions are worth knowing since they recur constantly: A4 at 2480 by 3508, A5 at 1748 by 2480, A3 at 3508 by 4961, all at 300 DPI. Every step up doubles the area, so the pixel count doubles too.

Where the arithmetic gets ignored

Print suppliers frequently reject files for being under a minimum resolution, and their minimum is usually applied at the finished size rather than at the file's tagged resolution.

Which means a file can be rejected despite being tagged 300 DPI, because the pixel count is insufficient for the size ordered. The tag was aspirational and the pixels were not there.

The check that avoids this is done before ordering: pixel dimensions divided by the ordered size, compared against the supplier's minimum. It takes ten seconds and prevents the exchange where a file is resubmitted three times with the metadata changed.

One habit removes most of the confusion for good: record assets by their pixel dimensions rather than by a resolution figure. A folder of images named or catalogued with their pixel width and height can be checked against any print size in seconds, where a folder of images described as 300 DPI tells you nothing until you open each one. The tag was somebody's intention at export; the pixel count is the file.