Change Image DPI

Print shops, publishers and application forms often ask for "300 dpi". DPI (dots per inch) is only a number stored in the file that says how big each pixel should be on paper, so changing it does not have to touch the picture. This tool rewrites that number directly in JPG, PNG, TIFF and BMP files, with no re-compression and no quality loss, and shows the print size that results. If you need more or fewer pixels for a print size, it can resample too. Files stay on your device.

How to use this tool

1. Choose one or more images.
2. Pick the DPI, for example 300 for printing or 72/96 for screens, or enter your own value.
3. Leave "Keep every pixel" to change only the stored value, or resample to a print width in centimetres or inches.
4. Download the files and check the print size shown for each one.

Formula

print width (in) = pixel width ÷ DPI; print width (cm) = pixel width ÷ DPI × 2.54

JPG: the JFIF header density is set (units = dots per inch), and EXIF and Photoshop resolution values are updated when present. A JPEG that stores RGB or CMYK colour directly (Adobe marker, no JFIF header) gets an EXIF resolution instead, because adding a JFIF header would change its colours. PNG: a pHYs chunk with round(DPI ÷ 0.0254) pixels per metre is written right after the header. TIFF: the XResolution and YResolution tags of every page. BMP: the pixels-per-metre fields. WebP, GIF and AVIF have no DPI field, so they are converted to PNG (JPG for HEIC).

Example

A 2480 × 3508 px scan at 300 dpi prints at 2480 ÷ 300 = 8.27 in = 21.0 × 29.7 cm, exactly A4. The same file marked 72 dpi would claim 34.4 × 48.7 inches, yet every pixel is identical. To print a 1000 px wide logo 5 cm wide at 300 dpi, resample: 5 ÷ 2.54 × 300 = 591 px.