Px to mm Converter: Pixels to cm & Inches by PPI
Px to mm Converter. Enter a pixel value and your PPI in this px to mm converter to get the size in millimeters, centimeters and inches. The free px to rem converter converts your input instantly, right in your browser.
Interactive Tool
96 PPI is the fixed CSS reference density used by browsers by default — it is a convention, not a measurement of your actual screen. Enter your display's real PPI above for a physically accurate result, or use the resolution + diagonal fields below to work it out.
Don't Know Your PPI? Calculate It
This px to mm converter turns a pixel value into real-world size by working out how big it is in millimeters, centimeters, and inches at a given pixel density. Enter your Pixels value and either type in a known PPI or fill in Resolution plus Screen Diagonal to have the PPI worked out for you, and the physical size updates as you type. There's also a Detect My Screen button that fills in your resolution automatically, though you'll still need to enter your screen's diagonal size yourself since a browser has no way to measure that.
Need to know how big a screen design will be once it leaves the monitor? This px to mm converter, a full px to mm/cm/inches converter, turns any pixel value into its physical equivalent in millimeters, centimeters and inches, using the resolution value you choose. A pixel is not a fixed measurement unit, so the answer depends on PPI, which is why this pixel converter asks for it before it gives you a size for print media, paper sizes or any other design job.
How to Use the Px to mm/cm/inches Converter
The tool works in both directions, so you can go from pixels to a physical size or from a physical size back to pixels.
- Enter the PPI. Leave the default PPI of 96 for web design and CSS work, or set 300 for a print job.
- Type the pixel value, or switch to printing mode and enter a width and height together.
- Read the result in millimeters, centimeters and inches at once.
- To go the other way (mm to px, or millimeters to pixels), type into the mm box instead.
Because the pixels to mm converter applies one formula at whatever resolution you set, the same 2,000-pixel image can come out as a poster or a postcard.
Pixel to Millimeter Conversion Formula
Every pixels to millimeters converter rests on one fact: 1 inch = 25.4 mm. Divide the pixels by the PPI to get inches, then multiply by 25.4: Use the free monitor viewing distance calculator any time you need a fast, accurate figure without doing the arithmetic yourself.
$$\text{mm} = \frac{\text{pixels}}{\text{PPI}} \times 25.4 \qquad \text{cm} = \frac{\text{pixels}}{\text{PPI}} \times 2.54 \qquad \text{in} = \frac{\text{pixels}}{\text{PPI}}$$For the web, the World Wide Web Consortium fixes a CSS pixel at 1/96th of an inch, so px to millimeters on screen is always \(25.4 \div 96 = 0.2646\) mm per pixel. That is the conversion formula behind every pixel to millimeters value at 96 PPI.
Convert Pixels to mm, Step by Step
Say you have a logo image that is 1,350 px wide and you want its print dimensions at 300 PPI:
- Pixels ÷ PPI: \(1350 \div 300 = 4.5\) in
- Inches × 25.4: \(4.5 \times 25.4 = 114.3\) mm, or 11.43 cm
The same pixel dimension at 96 PPI comes out at 357.19 mm (35.72 cm, 14.06 in), more than three times wider. A px to mm conversion is only right when the PPI matches where the file will end up.
Pixels to Inches, Centimeters and Typography Units
Pixels to inches is the first half of the formula (pixels ÷ PPI), and pixels to centimeters is the result × 2.54, or the mm figure ÷ 10. One cm is 10 mm. In typography, a CSS point is 1/72 in (4/3 px), a pica is 12 points (16 px) and a twip is 1/20 of a point.
PPI and DPI in Pixels to Millimeters Conversion
Pixels are samples, not lengths. PPI or DPI is the bridge that gives them a physical size, and picking it is the only real decision in the conversion. The free retina display distance calculator tool runs the calculation entirely in your browser — no data ever leaves your device.
What Is PPI (Pixels Per Inch)?
Pixels per inch counts how many pixels fit in one inch of a digital image. On the web, screen rendering uses 96 pixels per CSS inch regardless of the actual display or monitor, which is why a pixel measurement means something different from one screen size to the next.
DPI, Dots Per Inch and Print Resolution
Dots per inch describes how many ink dots a printer lays down per inch, so it measures print resolution and print quality. People use PPI and DPI interchangeably, and in photo editing apps such as Photoshop the "resolution" field is the number this converter needs. More dots per inch means a smaller, sharper result with better image quality.
Common Pixel Density Values by Use Case
There is no single right pixel density. These starting points cover most printing and photography work:
- Graphics and website images: 72-96 PPI for the web
- Draft proofs and newspapers: 150 PPI
- Photographs and magazines viewed up close: 300 PPI, the print standard
- Fine offset and gallery prints: 600 PPI for high quality
- Large-format banner or billboard viewed from a distance: 50 PPI or lower
In graphic design, start from these and adjust to how close people will stand.
Fitting a Photo to A3 with the Pixels to mm Converter
I have a landscape photo straight off the camera, 4,912 × 3,264 px, and a print lab order form that asks for A3 (420 × 297 mm under ISO 216). The question is simple: does this file fill the sheet at the 300 PPI print standard, and if not, what do I send instead?
The answer, up front: no, it falls 4.12 mm short on width at 300 PPI, but at 297.06 PPI it fills the 420 mm exactly, and that is what I send.
I switch the converter to printing mode, enter 4912 for width and 3264 for height, and set PPI to 300. The width works out as \(4912 \div 300 = 16.37\) in, times 25.4, so 415.88 mm; the height is 276.35 mm. That pixel to millimeter result tells me the print would leave a thin strip down one side of the sheet.
So I solve for the PPI that makes the width exactly 420 mm: \(4912 \div (420 \div 25.4) = 297.06\) PPI. I re-enter that value and the converter shows 420.00 mm × 279.09 mm. As a cross-check, 16.54 in × 25.4 gives 420.1 mm, which matches once rounding is accounted for.
| PPI | Width | Height | Fits A3? |
|---|---|---|---|
| 300 | 415.88 mm | 276.35 mm | 4.12 mm short |
| 297.06 | 420.00 mm | 279.09 mm | Width fills |
| 240 | 519.85 mm | 345.44 mm | Overflows |
What stands out is the height. Even at the right width, the photo is 279.09 mm tall on a 297 mm sheet, leaving about 8.96 mm of white border top and bottom. That has nothing to do with resolution: the camera's 3:2 frame is wider than the A-series 1:1.414 ratio, so no PPI setting makes both edges meet. Filling the height instead would need 279.14 PPI and crop roughly 27 mm off the width, which would cut into the subject.
My judgement: the drop from 300 to 297.06 PPI is about 1% and nobody will see it at arm's length, so resolution is not the input to worry about here. The aspect ratio is. I send the file at 297.06 PPI and tick the lab's "fit with border" option, rather than letting the lab's auto-crop decide what gets cut.
Pixel to Millimeters Conversion Table
Both tables were computed with the formula above.
Conversion Chart at 96 DPI: px, mm, cm and in
This conversion chart uses common screen widths, the values you meet most in web development.
| Pixels | Millimeters | Centimeters | Inches |
|---|---|---|---|
| 375 px | 99.22 mm | 9.92 cm | 3.91 in |
| 744 px | 196.85 mm | 19.69 cm | 7.75 in |
| 1024 px | 270.93 mm | 27.09 cm | 10.67 in |
| 1366 px | 361.42 mm | 36.14 cm | 14.23 in |
| 1440 px | 381.00 mm | 38.10 cm | 15.00 in |
| 2732 px | 722.84 mm | 72.28 cm | 28.46 in |
1px to mm at 72, 150, 300 and 600 DPI
The size of one pixel shrinks as density rises. At 300 dpi a pixel is about a third of its 96 DPI size.
| Resolution | 1 px in mm | px per mm |
|---|---|---|
| 72 DPI | 0.3528 mm | 2.83 px |
| 96 DPI | 0.2646 mm | 3.78 px |
| 150 DPI | 0.1693 mm | 5.91 px |
| 300 DPI | 0.0847 mm | 11.81 px |
| 600 DPI | 0.0423 mm | 23.62 px |
Pixel to mm Converter for Print Size and Physical Paper
To get a sharp print, work backwards: start from the paper and find the canvas you need. These are the standard paper sizes in mm with the pixels each needs at 150 and 300 DPI:
| Paper | Size in mm | Pixels at 150 DPI | Pixels at 300 DPI |
|---|---|---|---|
| Business card (EU) | 85 × 55 mm | 502 × 325 px | 1004 × 650 px |
| A6 | 105 × 148 mm | 620 × 874 px | 1240 × 1748 px |
| DL flyer | 99 × 210 mm | 585 × 1240 px | 1169 × 2480 px |
| A5 | 148 × 210 mm | 874 × 1240 px | 1748 × 2480 px |
| A4 | 210 × 297 mm | 1240 × 1754 px | 2480 × 3508 px |
| A3 | 297 × 420 mm | 1754 × 2480 px | 3508 × 4961 px |
If your file has fewer pixels than the 300 DPI column, the print size at 300 will come out smaller than the sheet. Lower the PPI and accept a softer photo, or ask the print shop what they need. A designer who checks this before sending a file saves a reprint.
Frequently Asked Questions
- How do I convert pixels to mm?
- Divide the pixel count by the PPI to get inches, then multiply by 25.4. For example, 1,350 px at 300 PPI is 4.5 inches, or 114.3 mm.
- How many millimeters is one pixel?
- It depends on the PPI. At the 96 PPI web default, one pixel is about 0.2646 mm. At 300 PPI it is about 0.0847 mm, and at 72 PPI about 0.3528 mm.
- What PPI should I use for print?
- 300 PPI is the usual standard for photos, flyers and magazines viewed up close. Large banners and posters seen from a distance can use 150 PPI or less, and fine offset work often uses 600.
- Why does the web use 96 PPI?
- CSS defines one pixel as 1/96th of an inch, so browsers treat 96 pixels as one inch regardless of the physical screen. That is why 96 PPI is the default for web and CSS conversions.
- Are PPI and DPI the same thing?
- They are often used interchangeably. PPI (pixels per inch) describes a digital image, while DPI (dots per inch) describes how many ink dots a printer places per inch. For a pixel to mm conversion, enter the same number either way.
- How do I convert pixels to centimeters or inches?
- Pixels divided by PPI gives inches. Multiply inches by 2.54 for centimeters, or by 25.4 for millimeters.
- How many pixels do I need for an A4 print?
- A4 is 210 × 297 mm, so at 300 PPI you need about 2480 × 3508 pixels. At 150 PPI, about 1240 × 1754 pixels is enough.