MM to Pixels Converter

How do you convert mm to pixels?

To convert mm to pixels, divide the millimeters by 25.4 to reach inches, then multiply by your resolution in DPI. The formula is pixels = mm / 25.4 x DPI. At 300 DPI, a 35 mm width is about 413 pixels.

Here's why that division matters. A millimeter isn't a fixed number of pixels on its own, because a pixel only has a real-world size once you fix the DPI. DPI means dots per inch, so it tells you how many pixels pack into one inch of print. There are exactly 25.4 mm in an inch, and that constant never changes, so it anchors the whole calculation. Pick a different DPI and the same 35 mm gives you a different pixel count every time.

A quick worked example: take 50 mm at 300 DPI. First, 50 / 25.4 = 1.969 inches. Then 1.969 x 300 = about 591 pixels. Drop the resolution to 96 DPI, the standard for screens, and that same 50 mm is only 189 pixels. Same physical length, very different pixel result, and that's the whole reason a plain "mm to pixels" answer doesn't exist without a DPI.

It also works in reverse, which is handy when a designer hands you a pixel file and you need the printed size. Just flip the formula to mm = pixels / DPI x 25.4. So a 600-pixel image at 300 DPI prints at 50.8 mm, and at 150 DPI that same 600 pixels stretches to 101.6 mm. The fewer dots you pack per inch, the bigger each pixel prints, which is exactly why low-DPI files look blocky when you blow them up.

ID, passport and business-card sizes in pixels

Here are the exact pixel dimensions for the small documents people convert most, like the 35x45 mm passport photo and the 86x54 mm card. Photo and ID work usually needs 300 DPI or higher, so that's the column you'll want.

A few notes on these presets so you don't get caught out. The 35x45 mm passport size is the international standard used across the UK, EU and most visa applications, and at 300 DPI it lands at 413x531 pixels. The US visa photo is the odd one out at 51x51 mm (the 2x2 inch square), which works out to 602x602 pixels. Business cards and CR80 ID cards both sit at 86x54 mm, so they share the same 1016x638 pixel footprint at 300 DPI. If your photo lab asks for 600 DPI, just read the right-hand column and you're set.

MM to pixels conversion chart

This chart covers the lengths people reach for most, from a single millimeter up to A4 page width. It's a fast reference when you don't want to open the tool, and every row assumes 300 DPI unless you change it.

You'll notice the numbers scale in a straight line. Double the millimeters and you double the pixels, because DPI stays fixed across the whole table. That's why 1 mm sits at roughly 12 pixels while 210 mm (the A4 short edge) hits about 2480 pixels. If you're working in centimeters or inches instead, the same logic holds, you just swap the 25.4 constant for 10 or 1 in the formula.

How do you use the mm to pixels converter?

The tool above does the math for you in three steps, and it won't make you remember the 25.4 constant. Here's the flow.

1. Type the length in millimeters.
2. Pick a DPI preset, or set a custom resolution.
3. Read the pixel result and copy it.

That's all there's to it. If you're prepping a file for print, set the DPI before you read the number, because changing it after is the most common mistake people make. The result updates live as you type, so you can test a few sizes without resetting anything.

What DPI should you use?

For print, 300 DPI is the default you'll reach for, and it's what nearly every photo lab and print shop expects. For screens you don't need anywhere near that, so 72 or 96 DPI does the job. Large-format banners can drop lower since they're viewed from a distance.

• 72-96 DPI for web and on-screen graphics. Anything higher just bloats the file without adding visible detail.
• 300 DPI for photos, ID images and business cards. This is the print standard and the safest pick when you're unsure.
• 600 DPI for fine line art, tiny text or when a passport service explicitly asks for it.
• 150 DPI for large banners and posters viewed from a few feet away, where the eye can't resolve the extra dots anyway.

If you're still not sure which number fits your project, our DPI guide breaks down each use case with examples so you don't over-spec or under-spec the file.

Frequently asked questions

How do you convert mm to pixels?

Divide the millimeters by 25.4 to get inches, then multiply by your DPI. The formula is pixels = mm / 25.4 x DPI. At 300 DPI, a 35 mm width is about 413 pixels.

How many pixels is a 35x45 mm passport photo?

At 300 DPI, a 35 x 45 mm passport photo is 413 x 531 pixels. At 600 DPI it's 827 x 1063 pixels. Most photo services ask for 300 DPI or higher.

What size is a business card in pixels?

A standard 86 x 54 mm business card is 1016 x 638 pixels at 300 DPI, the print standard. You'll want to add 3 mm bleed on each side for a print-ready file.

What DPI should I use for mm to pixels?

For print, 300 DPI is the safe default and it's what most photo labs expect. For screens you don't need that much, so 72 or 96 DPI is fine. Large banners can drop to 150 DPI.

How do I convert pixels back to mm?

Divide the pixels by your DPI, then multiply by 25.4: mm = pixels / DPI x 25.4. The pixels to mm converter handles it instantly without the math.