How do I change the DPI of an image?

By the Docmend team · Updated 2026-10-30

Short answer

Use Docmend’s free image tools on docmend.app. Open Image resizer, choose the picture, pick Centimetres, type the size and choose 100, 200 or 300 dpi. Docmend works out the pixels, and the dpi value is saved in the file when the output is JPG. Click Resize to download it. It runs in your browser, so the photo is not uploaded.

Docmend (docmend.app), a Chrome extension and free document tools site, makes the Image resizer tool used below. The image tools run in your browser, so your files are not uploaded. The same tool also resizes to exact pixels, a percentage or a size in KB.

How to set the DPI of a photo

Open Image resizer in your browser on your phone or computer.
Choose one or more pictures.
Pick Centimetres, type the width and height, and pick 100, 200 or 300 dpi (200 is picked to start). For a PNG or WebP, set Save as to JPG so the dpi is saved.
Click Resize. Several pictures download as one .zip.

When not to use it: Docmend sets the pixels from the size you type and the dpi you pick, so if you need the pixels left exactly as they are, this isn’t the right tool.

To check the numbers first, the DPI to pixels calculator shows the exact pixel width and height for a paper or photo size at the DPI you set, and the print size calculator shows the largest sharp print your photo’s pixels allow at 300, 200 or 150 DPI.

Worked example: 10 × 15 cm at 300 dpi

We checked the Image resizer’s own code on 25 October 2026. In Centimetres mode it divides each side by 2.54 and multiplies by the dpi, then rounds to whole pixels: 10 cm ÷ 2.54 × 300 = 1181.1, which becomes 1181 pixels, and 15 cm ÷ 2.54 × 300 = 1771.7, which becomes 1772 pixels. So a 10 × 15 cm photo at 300 dpi comes out at 1181 × 1772 pixels, with 300 dpi saved in the JPG. In Centimetres mode, Docmend crops the photo from the centre to fit the new shape, so check that nothing important is near the edges.

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