PX to MM Converter

This PX to MM converter lets you translate pixel values into real-world millimeters, instantly and accurately, based on your screen's DPI. No guesswork. No manual math.

Why Pixels and Millimeters Don't Match Up

Pixels are screen units. Millimeters are physical units. The two are connected by DPI (dots per inch), which tells you how many pixels fit inside one inch of screen space. Change the DPI and the same pixel value maps to a completely different physical size.

This matters most when you're designing for print, specifying UI dimensions for hardware teams, or working across devices with different pixel densities.

Common DPI Values

Screen / Context	DPI	1 px in mm
Web / Print default	72 DPI	0.3528 mm
Windows standard	96 DPI	0.2646 mm
125% display scaling	120 DPI	0.2117 mm
Retina / 2x displays	192 DPI	0.1323 mm

When You Need This Converter

• Preparing print-ready designs from screen mockups
• Converting UI specs to physical dimensions for hardware or embedded displays
• Working with CSS and design tools like Figma, Adobe XD, or Sketch
• Verifying that a layout will fit a specific physical screen size
• Communicating dimensions to manufacturers or print vendors

How to Use It

1. Select your screen DPI from the dropdown, or enter a custom value.
2. Type a pixel value into the input field.
3. Read the millimeter result instantly. Hit Copy or press Enter to grab it.
4. Use the swap button to convert MM back to PX.

How to Find Your Screen's DPI

On Windows, go to Settings → Display → Scale. A 100% scale typically means 96 DPI. On macOS, Retina displays run at 144 or 192 DPI. Most phones use 300+ DPI.

When in doubt, 96 DPI is the safe default for most screen-based work.

What Is a PX to MM Converter?

A PX to MM converter is a tool that transforms pixel values into millimeter measurements by using screen resolution as the bridge between the two unit systems.

Pixels are screen-relative units with no fixed physical size. Millimeters are absolute physical units that stay constant regardless of the display. The conversion requires knowing the PPI (pixels per inch) of the target device or workflow.

At the W3C CSS standard of 96 PPI, the relationship is fixed: 1px = 0.2646 mm.

Change the PPI and the output changes entirely. A pixel on a 72 PPI legacy print setup measures 0.3528 mm. That same pixel on a 300 DPI print workflow measures just 0.0847 mm.

Where it's used:

• Converting screen mockups into print-ready dimensions

• Matching UI element sizes to physical product specs

• Setting document dimensions in word processors and layout tools

• Writing accurate CSS print stylesheets

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What Is the Formula for Converting PX to MM?

The formula for converting pixels to millimeters is: mm = (px ÷ PPI) × 25.4

The number 25.4 represents the millimeters in one inch. Dividing pixels by PPI gives the measurement in inches. Multiplying by 25.4 converts that inch value into millimeters.

At 96 PPI (the CSS standard): mm = (px ÷ 96) × 25.4

PPI Value	1px in MM	Common Context
72 PPI	0.3528 mm	Legacy print, Illustrator default
96 PPI	0.2646 mm	CSS standard, web design
150 PPI	0.1693 mm	Medium-res print
300 PPI	0.0847 mm	High-quality print output

How PPI Affects the Conversion Result

PPI is not a screen property you can read automatically. It depends on both the resolution and the physical size of the display.

A 1920×1080 panel at 24 inches runs at 92 PPI. That same resolution on a 27-inch screen drops to 82 PPI (DisplayNinja, 2025). Average desktop PPI increased to 105 in 2024, up from 92 in 2020 (Gitnux, 2024).

This matters for conversions. If you assume 96 PPI on an actual 105 PPI display, your millimeter output will be slightly off from the real physical size.

For most web-to-print workflows, 96 PPI is still the correct default. It matches the CSS reference pixel spec, not a physical screen measurement.

What Happens at Non-Standard PPI Values

Non-standard PPI scenarios come up more than you'd expect:

• Retina and HiDPI displays (220–460 PPI on mobile) use logical pixels, not physical pixels

• Print bureaus sometimes specify 150 DPI for draft proofing

• Large-format print (banners, signage) can run at 72 DPI or lower since viewing distance increases

For Retina devices, work with logical pixels. The device handles scaling internally, so the 96 PPI default still applies to your CSS values.

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What Is the PX to MM Conversion Chart?

The table below lists common pixel values converted to millimeters at 96 PPI, the standard for web and CSS workflows.

Pixels (px)	Millimeters (mm) at 96 PPI	Millimeters (mm) at 72 PPI
1 px	0.265 mm	0.353 mm
4 px	1.058 mm	1.411 mm
8 px	2.117 mm	2.822 mm
12 px	3.175 mm	4.233 mm
16 px	4.233 mm	5.644 mm
24 px	6.350 mm	8.467 mm
32 px	8.467 mm	11.289 mm
48 px	12.700 mm	16.933 mm
64 px	16.933 mm	22.578 mm
96 px	25.400 mm	33.867 mm
128 px	33.867 mm	45.156 mm
256 px	67.733 mm	90.311 mm

The 72 PPI column applies when working in Adobe Illustrator with its default document resolution, or for older print workflows that follow the traditional points-based system.

Most-converted values in UI design are 16px, 24px, and 32px - these map to base spacing units in design systems like Material Design and Apple's Human Interface Guidelines.

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How Do You Convert PX to MM Manually?

Manual conversion takes 3 steps. No tools needed, just the formula.

Step 1: Identify your pixel value.

Step 2: Determine the PPI. Use 96 for web/CSS. Use 300 for high-res print. Use 72 if working in Illustrator with default settings.

Step 3: Apply the formula: mm = (px ÷ PPI) × 25.4

Worked example 1 (web context):

Converting 48px at 96 PPI: (48 ÷ 96) × 25.4 = 12.7 mm

Worked example 2 (print context):

Converting 300px at 72 PPI: (300 ÷ 72) × 25.4 = 105.83 mm

Worked example 3 (high-res print):

Converting 300px at 300 DPI: (300 ÷ 300) × 25.4 = 25.4 mm (exactly 1 inch)

The reverse conversion (mm to px) flips the formula: px = (mm × PPI) ÷ 25.4. This is what you need when a printer gives you physical dimensions and you need to build the canvas in pixels.

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Where Is PX to MM Conversion Used?

PX to MM conversion bridges digital design and physical output. The global digital print design market was valued at USD 38.07 billion in 2023 and is forecast to reach USD 57.03 billion by 2030 (Grand View Research, 2024), which reflects how common the screen-to-print workflow has become.

PX to MM in Print Design Workflows

Print production requires physical dimensions. Screen mockups work in pixels.

The gap between them: a designer builds a business card at 350×200px in Figma, then needs to hand off 89×51mm to the print bureau.

Adobe InDesign is the standard tool for resolving this. It works natively in millimeters and lets designers set up documents with bleed and trim marks in physical units from the start. Illustrator defaults to 72 PPI, which means conversion outputs differ slightly from CSS's 96 PPI baseline.

Canva handles this automatically for templated products (business cards, flyers, posters) by accepting pixel input and outputting print files at the correct physical size.

PX to MM in CSS Print Stylesheets

CSS supports mm as a native absolute unit. The catch: it only works accurately inside @media print rules.

@media print {
  .invoice-page {
    width: 210mm;
    height: 297mm; /* A4 */
    margin: 20mm;
  }
}

On screen, browsers convert mm to pixels using the 96 PPI assumption regardless of the actual display. So width: 210mm on a 92 PPI monitor will not measure exactly 210mm on screen. It will in print.

Knowing the px equivalent of your mm values lets you preview print layouts on screen with reasonable accuracy before sending to output.

PX to MM in UI and Product Design

Physical product design crosses into this territory constantly. A smartwatch face designed at 390×390px needs to match a 44mm circular display. A payment card design needs to fit 85.6×54mm (ISO/IEC 7810 standard). A label at 600×400px needs to output at exactly 150×100mm.

Without the conversion, there's no way to know if the digital asset will fit the physical object.

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Figma and Sketch: Built-In Unit Handling

Figma does not natively support millimeters as a working unit. All dimensions display in pixels. The workaround most designers use: set the canvas to the pixel equivalent of their target physical size at 96 PPI, then handle the conversion mentally or in export settings.

Sketch has limited mm support. You can set ruler units to millimeters under Preferences, but internal values still calculate in pixels. Helpful for reading off dimensions, but not for entering mm values directly.

Neither tool is ideal for print-first workflows. InDesign handles that correctly from document setup through to export.

Online Converter Tools: What to Look for

The most useful converters let you set a custom PPI value rather than locking to 96. That matters when working across different output contexts.

For print work, look for tools with a dedicated 300 DPI mode that converts width and height simultaneously. Having to convert x and y dimensions separately wastes time on every asset.

MM to PX conversion is just as common as the reverse. If a tool only handles one direction, it covers only half the workflow. The same applies to related conversions: PX to CM, PX to inches, and PX to PT all come up regularly depending on whether you're working in metric, imperial, or typographic units.

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How Does Screen Resolution Change the PX to MM Result?

Screen resolution changes the PX to MM result because PPI varies by display, and the formula depends entirely on PPI as its conversion factor.

The same 100px element has a different physical size on every display with a different PPI. At 92 PPI (a standard 24-inch 1080p monitor), 100px = 27.6mm. At 460 PPI (iPhone 15 Pro Max), 100px = 5.5mm.

As of 2024, the most popular desktop resolution is 1920×1080 with 23.12% global market share (StatCounter, 2024). Average desktop PPI reached 105 in 2024, up from 92 in 2020 (Gitnux, 2024).

Logical Pixels vs. Physical Pixels on Retina Displays

Apple Retina displays and Android HiDPI screens use a device pixel ratio (DPR) to scale content.

A MacBook Pro 14-inch (2021) has a physical resolution of 3024×1964 at 254 PPI. But macOS reports a logical resolution of 1512×982 at 2× DPR. CSS sees the logical pixels.

So when you write width: 100px in CSS, that renders as 200 physical pixels on a 2× Retina display. The logical pixel is the CSS pixel. The physical pixel is what the screen actually lights up.

For mm conversion purposes, always work with logical pixels (CSS pixels), not physical device pixels. The 96 PPI default in CSS refers to the logical pixel, not the hardware pixel.

Which PPI Value to Use for Different Devices

Use 96 PPI for:

• CSS and web design (W3C standard)

• Screen mockup previews

• Most online converter tools

Use 72 PPI for:

• Adobe Illustrator documents (default)

• Legacy print workflows based on the PostScript point system

• PT to PX conversions in typographic contexts

Use 300 PPI for:

• High-quality print output (brochures, business cards, packaging)

• Any asset going to a commercial printer

• Photoshop canvas setup for print

Microsoft's display guidelines recommend 90–110 PPI for desktop monitors at arm's length (ACEMAGIC, 2025). That range straddles the 96 PPI CSS default, which is why it remains a reliable assumption for most screen-based work.

What Is the Difference Between PX, MM, CM, PT, and EM?

Each CSS length unit serves a different purpose. Using the wrong one in the wrong context produces either unpredictable screen layouts or incorrectly sized print output.

Unit	Type	Fixed Physical Size	Best For
px	Absolute (CSS)	No (device-dependent)	Screen layouts, UI design
mm	Absolute	Yes (in print)	Print stylesheets, physical specs
cm	Absolute	Yes (in print)	Larger print dimensions
pt	Absolute	Yes (in print)	Typography, print font sizes
em	Relative	No	Scalable font sizing, responsive layouts

Key difference: px, mm, cm, and pt are all absolute units. Only em and rem are truly relative. That said, mm behaves as an absolute unit only in print contexts. On screen, browsers convert mm to pixels using the 96 PPI assumption, so a 10mm element on screen does not measure 10mm on a ruler.

According to the W3C CSS specification, CSS abandoned the requirement for mm to display accurately on screen in 2011. Physical units like mm and cm must work correctly only on printed output and on high-resolution devices.

1in = 25.4mm = 2.54cm = 72pt = 6pc

That relationship holds across all absolute units. Converting between them is straightforward once you know the inch as the base.

PX vs MM

PX: Screen-relative. No fixed physical size. 100px at 92 PPI renders at 27.6mm on a monitor, but the same 100px at 460 PPI (iPhone 15 Pro Max) renders at just 5.5mm physically.

MM: Physically fixed in print. Unreliable on screen. Use mm when the final output has physical dimensions that must match exactly, such as packaging, labels, or business cards.

PT vs MM

PT is the traditional typography unit inherited from print.

• 1 pt = 0.3528 mm (at 72 PPI)

• 12 pt = 1 pica

• 72 pt = 1 inch

PT is worth knowing if you're converting from older print files or working in Adobe Illustrator, which defaults to 72 PPI and uses pt natively in its type panels. PT to CM conversion follows the same 25.4mm base, just at the 72 PPI reference.

EM vs MM

EM is a relative unit. It scales with the parent element's font size.

Not directly convertible to mm unless a base font size is declared. 1em at a 16px root = 16px. That 16px at 96 PPI = 4.233mm. Change the root font size and the mm equivalent changes with it.

For typographic hierarchy, em and rem give scalability that mm never can. For physical sizing, mm wins every time.

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How Do You Use MM Units in CSS?

CSS supports mm as a native absolute unit. It resolves against the same base as all other absolute CSS lengths: 1in = 25.4mm = 96px (per the W3C CSS specification).

On screen, this means width: 25.4mm renders at exactly 96px regardless of actual display PPI. On paper, it renders at exactly 25.4 physical millimeters.

Using MM in @media print Stylesheets

Print stylesheets are where mm actually performs correctly.

@media print {
  .page {
    width: 210mm;
    height: 297mm;   /* A4 */
    margin: 20mm;
    padding: 15mm;
  }

  .header {
    font-size: 14pt;
    margin-bottom: 8mm;
  }
}

CSS-Tricks documented real-world use of mm measurements in print stylesheets for dynamically generated barcoded label PDFs, confirming it as a legitimate production approach (CSS-Tricks, 2020).

Common uses inside @media print:

• Page dimensions and margins matching paper size standards

• Bleed allowances (typically 3mm for professional print)

• Column widths in multi-column print layouts

• Spacing between print elements that must align with physical rulers

Why MM Units Fail on Screen CSS

Using mm outside of @media print causes a predictable problem.

Browsers convert mm to pixels using the fixed 96 PPI assumption, not the actual screen PPI. A 27-inch 1080p monitor runs at 82 PPI. On that screen, width: 25.4mm renders as 96px but physically measures 29.7mm (not 25.4mm).

Uxcel's CSS documentation confirms this directly: the same 60×60mm element looks different on a 24-inch desktop display versus a 6-inch smartphone screen, not to mention viewing distance differences (Uxcel, 2024).

The rule is simple: use px for screen, mm for print. Don't mix them in the same stylesheet context without a media query wrapper.

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What Are the Standard Paper Sizes in PX and MM?

Paper sizes defined by ISO 216 are fixed in millimeters. Converting them to pixels requires a specific DPI value. Use 96 PPI for screen mockups, 300 DPI for print-ready files.

A4 is the most widely used paper size globally, the standard for documents, letters, and forms in over 160 countries (ISO 216 standard). The United States and Canada use Letter size instead.

Paper Size	MM Dimensions	Pixels at 96 PPI	Pixels at 300 DPI
A3	297 × 420 mm	1123 × 1587 px	3508 × 4961 px
A4	210 × 297 mm	794 × 1123 px	2480 × 3508 px
A5	148 × 210 mm	559 × 794 px	1748 × 2480 px
A6	105 × 148 mm	397 × 559 px	1240 × 1748 px
US Letter	216 × 279 mm	816 × 1056 px	2550 × 3300 px
Business Card	85.6 × 54 mm	323 × 204 px	1004 × 638 px

96 PPI vs 300 DPI: which to use?

Use 96 PPI dimensions when setting up screen mockups, CSS print previews, or PDF thumbnails. Use 300 DPI dimensions when sending files to commercial printers, packaging suppliers, or any production workflow where physical quality matters.

A4 at 300 DPI (2480 × 3508 px) produces roughly 9x more pixels than at 96 PPI (794 × 1123 px). That difference translates directly into print sharpness. Low-res files sent to print bureaus are one of the most common handoff errors in screen-to-print workflows.

Note on A4 vs Letter: A4 (210 × 297mm) is taller and slightly narrower than US Letter (215.9 × 279.4mm). Printing an A4-formatted document on Letter stock without adjusting settings shifts margins and can clip content.

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How Is PX to MM Conversion Handled in Design Software?

Each major design tool treats pixel-to-mm conversion differently. The approach depends on the tool's default PPI and its intended output (screen vs. print).

Figma's internal DPI is 72 PPI, not 96, which means its mm-to-pixel conversion follows: value × 72 ÷ 25.4 (Figma Community, 2023). This differs from CSS's 96 PPI baseline, making direct spec handoffs between Figma and print workflows tricky without accounting for the PPI mismatch.

Figma: Working with MM Without Native Support

Figma's default unit is the pixel. It does not support mm as a native working unit.

Practical workarounds designers use:

• Third-party plugins (Uniter, Millimeters, Unit Converter) for real-time mm input

• Convert the target physical size to pixels at 96 PPI, then set up the Figma frame at those pixel dimensions

• Use "Print for Figma" plugin for standard paper sizes, bleed, and CMYK PDF export

The "Print for Figma" plugin includes presets for A4, Letter, A5, and business cards. It handles DPI management and crop marks without leaving Figma.

Adobe Illustrator and Photoshop: Document Resolution Settings

Illustrator defaults: 72 PPI document resolution. Units switchable to mm under File > Document Setup. The 72 PPI default means pixel values differ from CSS conversions.

Photoshop approach: Set canvas to mm directly when creating a new document. Enter the target physical dimensions plus resolution. At 300 DPI on an A4 canvas, Photoshop calculates 2480 × 3508 px automatically.

A common trap: opening a 96 PPI screen design in Illustrator (72 PPI default) produces a slightly larger physical document than intended because Illustrator and CSS use different PPI baselines.

InDesign: The Print-First Unit System

InDesign works natively in millimeters from document creation. No conversion needed.

Set up a new document with physical dimensions in mm, specify bleed in mm, and InDesign handles all internal calculations. It's the tool that eliminates the px-to-mm problem entirely by never requiring pixel input in the first place.

The handoff reality: most web design starts in Figma and ends in InDesign for print. The px-to-mm conversion happens at that transition point. Knowing the PPI difference between the two tools (72 vs 96) prevents sizing errors before they reach the printer.

For color accuracy at this stage, understanding the difference between RGB (screen) and CMYK (print) is just as relevant as getting the physical dimensions right. Related unit conversions that come up at this stage include PX to EM for responsive screen layouts and PX to REM for CSS design systems, while CM to PX handles the reverse direction when physical specs need to become digital assets.

FAQ on PX To MM Converters

How many mm is 1px?

At the CSS standard of 96 PPI, 1px equals 0.2646 mm.

At 72 PPI (Adobe Illustrator's default), 1px equals 0.3528 mm. The result always depends on which PPI value applies to your workflow.

What is the formula to convert px to mm?

The formula is: mm = (px ÷ PPI) × 25.4

Divide your pixel value by the PPI, then multiply by 25.4 (millimeters per inch). For web and CSS work, use 96 PPI. For high-quality print output, use 300 PPI.

How many px is 1 mm?

At 96 PPI, 1 mm equals 3.7795 px.

At 300 DPI (print), 1 mm equals 11.811 px. Use the MM to PX converter when working from physical dimensions back to pixel values.

Why does PPI matter for px to mm conversion?

Pixels have no fixed physical size. Their real-world measurement depends entirely on the display or output device's pixel density.

Change the PPI and the millimeter output changes. 100px at 96 PPI = 26.46 mm. The same 100px at 300 PPI = 8.47 mm.

What PPI should I use for print conversion?

Use 300 PPI for commercial print work (brochures, packaging, business cards).

Use 150 PPI for draft proofing. Use 96 PPI only for screen mockups or CSS print stylesheet previews, not for files going to a professional printer.

How do I convert px to mm in CSS?

CSS supports mm natively as an absolute unit. Inside an @media print block, width: 210mm renders accurately.

On screen, browsers convert mm to px using the fixed 96 PPI assumption regardless of actual display density, so physical accuracy only holds in print output.

What is 1920px in mm?

At 96 PPI: (1920 ÷ 96) × 25.4 = 508 mm.

At 72 PPI: (1920 ÷ 72) × 25.4 = 677.3 mm. Always confirm which PPI applies before using the result in a print or physical design context.

How do px to mm conversions work in Figma?

Figma works exclusively in pixels. Its internal resolution is 72 PPI, not 96.

To work in mm, use a plugin like Uniter or Millimeters. For print-ready output, the Print for Figma plugin handles paper sizes, bleed, and DPI management without switching to InDesign.

What is the difference between DPI and PPI in conversions?

PPI (pixels per inch) describes screen or image resolution. DPI (dots per inch) describes printer resolution.

For px to mm conversion, PPI is the relevant value. In practice, most designers use the terms interchangeably when setting up conversion calculations, though they refer to different physical processes.

How many px is an A4 page?

A4 is 210 × 297 mm. At 96 PPI, that converts to 794 × 1123 px.

At 300 DPI for high-quality print, A4 requires 2480 × 3508 px. Using the 96 PPI dimensions for a print file will result in a low-resolution output.