DPI-aware converter
Pixel to MM Converter With DPI
Enter width, height, and DPI for an exact physical-size conversion. If your screen or file DPI is unknown, use the calibration controls to calculate it from a measured reference.
Live conversion
Enter dimensions
Converted size
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mm = pixels × 25.4 ÷ DPI Enter valid dimensions to see the calculation.
Calculations stay in your browser. No dimensions are uploaded.
Unknown DPI?
Calibrate from a measured reference
Measure a known pixel length on the screen or page, then enter its physical length. The derived DPI is applied to the main calculator.
Reference DPI: 96
Three-step workflow
How to use this calculator
Enter the pixel dimensions
Use the image, canvas, or measured on-screen width and height in pixels.
Set or calibrate DPI
Choose a common DPI, type a custom value, or derive DPI from a pixel reference measured in millimeters.
Read the physical size
The calculator returns millimeters, inches, diagonal size, aspect ratio, and the live formula.
Practical guide
How DPI calibration improves pixel-to-mm accuracy
Pixels have no universal physical size. The same 500-pixel object can measure differently on two screens or when printed at two resolutions. DPI supplies the missing scale: it describes how many pixels or dots occupy one inch.
For a measured reference, DPI is calculated as pixels multiplied by 25.4 and divided by the measured millimeters. The resulting DPI is then used for both width and height conversions.
Official reference: Microsoft DPI and device-independent pixel guidance ↗Common questions
DPI & Calibration FAQ
Can pixels be converted to millimeters without DPI?
Not to a unique physical size. You need an assumed DPI or a calibrated pixels-per-inch value.
How do I calibrate an unknown DPI?
Display or identify a known pixel length, measure it in millimeters, and enter both values in the calibration panel.
Is PPI the same as DPI here?
PPI technically describes image or display pixels while DPI describes printer dots, but both serve as the density value in this size formula.
Why is 96 DPI the default?
96 DPI is the standard CSS reference density and a common neutral default for Windows-oriented screen calculations.
Specialized tools
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