We use cookies.This website uses essential cookies to operate core features. With your consent, we also use analytics cookies to understand traffic and improve the service. For more details, see our .
We use cookies.This website uses essential cookies to operate core features. With your consent, we also use analytics cookies to understand traffic and improve the service. For more details, see our .
Was this tool helpful to use?
Your feedback helps us make it better
Convert between pixels and millimeters based on PPI density. Supports custom density values, ideal for UI design and print layout.
A pixel count needs a pixel-density value before it can represent a physical length. The formula is millimeters = pixels × 25.4 ÷ PPI. This calculator also works in reverse, converting a millimeter length into the pixel count required at the selected PPI.
The tool performs arithmetic only. It does not upload, resample, or change an image.
At 96 PPI, 1 pixel is about 0.2646 mm and 100 pixels is about 26.4583 mm. At 300 PPI, 100 pixels is about 8.4667 mm. In reverse, a 50 mm image at 300 PPI needs about 590.55 pixels, normally rounded according to the destination application.
CSS defines a reference relationship in which 96px equals one inch, or 25.4 mm. A browser may map one CSS pixel to multiple device pixels on a high-density screen. For web layout, converting CSS px at the 96 reference ratio is a unit conversion; it does not guarantee that an element will measure the same number of millimeters with a physical ruler on every device.
For an image or print file, use the image pixel dimensions and the intended PPI. A print provider may specify 300 PPI or another value based on the process and viewing distance. Printer DPI describes output dots and is not necessarily identical to image PPI. Confirm bleed, crop, and final dimensions separately.
Phone and computer specifications often list physical panel pixels, while interfaces may use logical pixels affected by device pixel ratio and operating-system scaling. Use the pixel count that belongs to your actual task. Mixing a CSS layout width with a display’s hardware PPI can produce a misleading physical measurement.
The converter displays a practical decimal result, but a raster canvas ultimately uses whole pixels. Decide whether to round up, down, or to the nearest pixel based on the output requirement. Repeated conversions can introduce small rounding differences, so retain the original value when accuracy matters.
If the result seems wrong, check that PPI is positive and that you have not entered printer DPI in place of image PPI without confirming the workflow. Changing PPI metadata alone does not create new image detail. This page does not assess sharpness, printer quality, browser zoom, device scaling, or the accuracy of a display’s advertised size.