MM to PX Converter Online
with Conversion Table

In the world of design and development, we're constantly translating ideas between two different worlds: the physical and the digital. A client might hand you a beautiful brand guide with a logo size specified in millimeters (mm), but on the web, we speak in pixels (px). How do you bridge that gap accurately?

As an agency founder, I’ve seen our team tackle this exact challenge daily. Guesswork isn't an option when brand consistency is on the line. That's why we built this simple mm to px converter. It’s a tool born from our own workflow, designed to make the translation from print-ready specs to pixel-perfect screens instant and accurate.

What is a Millimeter (mm) and a Pixel (px)?

Before we dive in, let's clarify what we're converting. Understanding the “why” makes the “how” much more powerful.

• Millimeter (mm): A millimeter is an absolute, physical unit of length. It's part of the metric system, equal to one-thousandth of a meter. A millimeter has the same, fixed size whether it's on a ruler, a piece of paper, or a business card. It's tangible and real.

• Pixel (px): A pixel (short for “picture element”) is a relative, digital unit. It's the smallest controllable dot of light on a digital screen. The key word here is relative. A pixel has no fixed, real-world size. Its physical size depends entirely on the screen's resolution, or how many pixels are packed into a certain area.

The fundamental challenge is converting an absolute physical measurement (mm) into a relative digital one (px).

Why Convert Millimeters to Pixels?

This conversion is a critical step in many creative and technical projects. If you've ever been frustrated trying to make a website element “look” the same size as a printed mockup, this is the problem you were facing.

Real-world use cases happen every day at our agency:

• Web Design: A client's branding guidelines (often made for print) dictate, “The logo must be 50mm wide.” You can't just type width: 50mm; in your CSS—it's unreliable. You need to convert 50mm to pixels to ensure it renders correctly and consistently in a web browser.

• UI/UX Design: When designing an app interface that needs to reflect real-world dimensions (like a virtual ruler or a mockup of a physical product), you need to know the pixel equivalent of its physical size.

• Print-to-Web Projects: A team might be tasked with converting a magazine layout or a physical advertisement into a series of digital banner ads. All the specs from the print version (margins, font sizes, image dimensions) will be in mm or cm and must be translated to px for the digital version.

• Responsive Design: While we primarily use relative units like rem and % for responsive layouts, the “base” for these calculations often starts with a pixel value. Getting that initial pixel value right, based on a physical spec, is crucial.

The Key: Understanding the Dependency Variable (PPI/DPI)

Here is the most important concept in this entire conversion: You cannot convert mm to px without a “translator.”

That translator is PPI (Pixels Per Inch).

• What is PPI? PPI stands for Pixels Per Inch. It's a measure of screen resolution—specifically, how many pixels are packed into one physical inch of a screen.

• What about DPI? You'll also hear DPI (Dots Per Inch), which technically refers to printer resolution (how many dots of ink a printer places in an inch). In the digital world, the terms are often used interchangeably, but PPI is the correct one for screens.

A screen with a high PPI (like a smartphone) packs many small pixels into one inch. A screen with a low PPI (like an old desktop monitor) has fewer, larger pixels in the same space.

This is why a 50mm line will be made of more pixels on a high-PPI “Retina” display than on a standard-PPI monitor.

Common PPI Values to Know:

• 96 PPI: This is the standard for web and CSS. For decades, browsers have used 96 PPI as the reference value to translate physical units. When you set a CSS property to 1in, the browser attempts to render it as 96px.

• 72 PPI: An older standard, originally from “classic” Apple Macintosh displays. You'll still see it used, but 96 PPI is the modern web standard.

• 300 PPI: This is the standard for high-quality print. If you're preparing a digital image to be printed, you'll almost always work at 300 PPI (or DPI).

For any mm to px conversion for web design, 96 PPI is almost always the number you should use.

The Conversion Formula + Example Calculation

The math itself is straightforward. It's a two-step process:

1. First, convert your millimeters to inches (since PPI is Pixels Per Inch).

2. Second, multiply the inch value by your target PPI.

There are 25.4 millimeters in one inch.

The Formula: Pixels (px) = (Millimeters (mm) / 25.4) * PPI

Example 1: Converting for the Web (96 PPI)

Let's convert our client's 50mm logo for their website.

• Step 1 (mm to inches): 50mm / 25.4 = 1.9685 inches

• Step 2 (Inches to Pixels): 1.9685 in * 96 PPI = 189.96px

• Result: You would set your logo's width to 190px (rounding to the nearest whole pixel).

Example 2: Converting for Print (300 PPI)

Now, let's say you're creating a digital file (in Photoshop) for a brochure, and the spec is also 50mm.

• Step 1 (mm to inches): 50mm / 25.4 = 1.9685 inches

• Step 2 (Inches to Pixels): 1.9685 in * 300 PPI = 590.55px

• Result: Your digital file should have the logo at 591px wide to ensure it prints correctly at 50mm.

The difference is huge (190px vs. 591px). This is why knowing your target PPI is essential—and why a reliable tool is so much faster.

How to Use Our Simple MM to PX Converter

We designed our mm to px converter to be fast, accurate, and foolproof. No more manual math or hunting for formulas.

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Here’s how to use it:

1. Enter Your Millimeter Value: In the first field, type the number of millimeters you want to convert (e.g., 50).

2. Select Your PPI (Pixels Per Inch): This is the crucial step. We've included the most common values as presets.

   • Choose 96 PPI for all standard web/CSS conversions.

   • Choose 300 PPI if you are working on a high-resolution file for print.

   • You can also type a Custom PPI if you know the exact specs of a specific device.

3. Get Your Result Instantly: The “Pixels (px)” field updates in real-time. No “submit” button needed.

4. Copy the Value: Click the “Copy” button to instantly grab the pixel value. You can paste it directly into your CSS file, Figma, Sketch, or Photoshop.

Advantages + Use Cases (The Founder's Voice)

From an agency founder's perspective, efficiency is everything. Every minute a designer or developer spends fumbling with a calculator is a minute not spent on creative problem-solving. We built this tool suite to shave off those minutes and reduce friction in our workflow.

The advantages are simple but powerful:

• Speed: Get an instant, accurate answer.

• Accuracy: It eliminates human error. Mistyping 25.4 as 2.54 can break a layout, but the tool is always correct.

• Consistency: This is the big one for me. When our entire team uses the same mm to px converter, we guarantee consistency. A 50mm spec from a brief always becomes 190px (at 96 PPI), no matter which designer or developer picks up the task. This is vital for brand integrity.

• Client Clarity: We often share these tools with clients. It helps them understand why their 50mm logo on paper translates to 190px on a screen, demystifying the “magic” of digital design.

It becomes a part of the daily workflow for sizing padding, margins, width, height, and font-size, ensuring all elements derived from a print spec are translated perfectly to the web.

Best Practices for Converting MM to PX

A tool is only as good as the person using it. Here are our pro tips for getting this conversion right every time.

1. The Golden Rule: Know Your PPI. I can't say it enough. Before you convert, ask “What is this for?” If the answer is “the website,” use 96 PPI. If it's “a high-res print file,” use 300 PPI.

2. Don't Use mm Units in CSS. This is a common mistake for beginners. While CSS technically allows you to write width: 50mm;, it is extremely unreliable. The browser has to guess your monitor's PPI to render it, and it's almost always wrong. The result is an element that is a different physical size on every single screen. Always use this converter to find the pixel equivalent (e.g., width: 190px;) for consistent layouts.

3. Round to the Nearest Whole Pixel. You'll often get a decimal result (like 189.96px). Since a pixel is the smallest whole unit, it's best practice to round to the nearest integer (e.g., 190px).

4. Talk to Your Printer. If you're converting from px to mm for a print job, always ask the print shop for their required DPI. Don't just assume 300.