A size in centimetres is two numbers
A centimetre size only becomes a picture when it is paired with a resolution. At 300 dpi, a common print figure, each centimetre is 118.11 pixels; at 200 dpi it is 78.74. The panel holds the print size you type and computes the pixels, then reports the size those whole pixels actually make — so what you read is what the file will say.
| Size | Pixels | Achieved |
|---|---|---|
| 3.5 cm | 413 px | 3.50 cm |
| 10 cm | 1181 px | 10.00 cm |
| 15 cm | 1772 px | 15.00 cm |
| 210 mm | 2480 px | 210.0 mm |
| 6 in | 1800 px | 6.00 in |
What a size cannot do
- Making a small picture large in centimetres at a high DPI interpolates new pixels; it adds no detail. The verdict under the print size says how the density will read on paper.
- WebP and GIF carry no resolution most tools read, so the stated size travels with you, not with the file. Write JPEG or PNG when the DPI matters.
Questions about centimetres and DPI
How many pixels is 10 cm?
It depends entirely on the resolution. 10 cm is 3.937 inches, so at 300 dpi it is 1181 pixels, at 200 dpi 787, and at 72 dpi 283. A centimetre size on its own does not fix a pixel count; the size and the DPI together do, and the panel shows both.
Why did my 10 cm come back as 9.98 cm?
Because a file holds whole pixels. At 72 dpi, 10 cm is 283.46 pixels, the file gets 283, and 283 pixels at 72 dpi measure 9.98 cm. The panel reports the size the whole pixels actually make rather than echoing the request back. At 300 dpi the difference is never more than half a pixel, under 0.005 cm, and disappears at two decimals.
Do I need to resample, or only change the DPI?
If the picture already has enough pixels and only the stated size is wrong, change only the DPI: the pixels are copied through untouched and the file states a new print size. If a form or printer asks for a specific pixel count at a specific size, resample. The Output panel tells you when a size is reachable without touching a pixel.
Does the DPI get written into the file?
Yes, for JPEG and PNG. A JPEG gets it in the JFIF header, and in its Exif block too when the file has one, set to agree; a PNG gets a pHYs chunk. The saved file is read back and the receipt states which containers carry it.
Millimetres or inches instead?
Use the unit chips under the print size fields, or press U. The pixel arithmetic is the same; only the display changes.
Related measurements
Only the stated size wrong? Change the DPI and leave every pixel alone.
- Change DPIRewrite the density tag without touching a pixel.
- Print size calculatorPixel dimensions, centimetres, inches and density kept visibly linked.
- 300 dpiThe number a print vendor asks for, written into the file.
- Change image size in pixelsA box in pixels: fit inside, fill and crop, or stretch, with the factor printed.
