96 DPI — the CSS reference pixel used by browsers and UI design
150 DPI — draft-quality print, quick proofs
300 DPI — standard for print production (brochures, magazines)
600 DPI — fine art prints and large-format signage
How to use
1
Type a size
Enter a value into any row — mm, cm, inch or px — and the other three update instantly.
2
Set the DPI
Pick a preset (72 / 96 / 150 / 300 / 600) or type a custom value from 1 to 2400. Pixel values recalculate live as you change it. If a print shop has asked for 300 and you are not sure what that request covers, our 300 DPI guide takes it apart.
3
Choose a paper size
Select an ISO A or B size, US Letter, Legal or Tabloid, or a business card, credit card or postcard preset, then toggle portrait or landscape.
4
Add bleed and safe margin
Set bleed and safe margin in mm to see the trim size, the size with bleed, and the safe area in both mm and px.
From a measured size to an artboard
Print work starts with a physical measurement and ends with a canvas counted in pixels. Below are the pieces designers size most often, converted at the print standard of 300 DPI: the trim size you were given, the canvas once bleed is added, and the safe area left over for text once you pull back from the cut line.
Piece
Trim (mm)
Artboard (px)
With 3 mm bleed (px)
Safe area, 5 mm in (px)
Business card
90 × 54
1063 × 638
1134 × 709
945 × 520
Postcard
100 × 148
1181 × 1748
1252 × 1819
1063 × 1630
A5 flyer
148 × 210
1748 × 2480
1819 × 2551
1630 × 2362
A4 leaflet
210 × 297
2480 × 3508
2551 × 3579
2362 × 3390
A3 poster
297 × 420
3508 × 4961
3579 × 5031
3390 × 4843
Every figure comes from px = mm ÷ 25.4 × DPI, rounded to the nearest whole pixel — so converting a full size in one step and adding up converted parts can land a pixel apart. The 3 mm bleed and 5 mm safe margin are common starting points, not standards: ask the printer for the values they want before you build the file.
Four jobs that start with a ruler
Millimetres come from the physical world — a card in your hand, a wall you measured, a spec sheet from a print shop. How many pixels that becomes depends entirely on what happens to the file afterwards.
Laying out a business card
A 90 × 54 mm card at 300 DPI is a 1063 × 638 px artboard. Add the usual 3 mm bleed on all four sides and the canvas you actually paint on grows to 1134 × 709 px, while pulling 5 mm back from the trim leaves a safe area of 945 × 520 px. That safe width is the real constraint on the design: a name, a role, a phone number and an email all have to live inside 945 px, not the 1134 px you can see. When a supplied logo has to fill part of that width, the px to mm converter tells you how many millimetres its pixels are actually worth.
A sign you measured with a tape
A 700 × 500 mm window sign at 300 DPI works out to 8268 × 5906 px — about 48.8 megapixels, heavy to edit and rarely necessary. Large-format printing is read from further away, so 150 DPI (4134 × 2953 px, roughly 12.2 megapixels, a quarter of the pixels) is a common working resolution for signage, and some banners are built lower still. Get the required resolution at final size from the printer before you commit to an artboard, and keep in mind that the DPI field stored in a file is only a label — the pixel count is what decides how large the piece can print.
Artwork for merchandise printing
Print-on-demand vendors publish their print area in millimetres, and a 280 × 380 mm front panel is typical for an adult tee. At 300 DPI that is a 3307 × 4488 px file; at the 150 DPI many garment printers accept it halves on each axis to 1654 × 2244 px. Vendors usually cap the upload size too, so when a 300 DPI PNG is rejected for weight rather than resolution, the image compressor brings the file down without touching its pixel dimensions.
A screen design specified in millimetres
Kiosk and signage briefs often arrive in millimetres even when the output is a display. CSS anchors its physical units to 96 px per inch, so 1 mm resolves to 3.7795 px and a 10 mm touch target lands on 38 px — the same answer this converter gives with the DPI set to 96. Treat those units as nominal rather than physical, because a browser has no way of knowing how large the screen in front of it really is. Our A4 pixel reference runs the same 96 DPI arithmetic across a whole page.
Frequently asked questions
What is A4 in pixels at 300 DPI?
A4 is 210 × 297 mm. At the print standard of 300 DPI that’s 2480 × 3508 px (210 ÷ 25.4 × 300, rounded). At 150 DPI it’s 1240 × 1754 px, and at 72 DPI it’s 595 × 842 px.
Why does CSS use 96 DPI?
Browsers and OS UI frameworks have used 96 DPI (96 px per inch) as the screen pixel reference since the 1990s. CSS defines its px unit against that same 96 DPI baseline, so it’s the number used whenever inches or points are converted to px.
What is bleed, and why is 3 mm the default?
Bleed is extra artwork drawn past the trim line so a small misalignment when a printer cuts the sheet doesn’t leave a white edge. 3 mm is a common print-shop default, but always confirm the exact figure your printer requires before sending final files.
What’s the difference between DPI and PPI?
Strictly, DPI (dots per inch) describes a printer’s ink-dot density, while PPI (pixels per inch) describes a digital image’s pixel density. Design tools often use the terms interchangeably — this tool uses DPI since that’s the more familiar term for print work.
Why is my exported image too small to print?
Exporting at the screen default of 72 DPI produces far fewer pixels than 300 DPI for the same physical size, since px = mm ÷ 25.4 × DPI. Check the pixel size at your target DPI here before exporting.
What’s the difference between safe margin and bleed?
Bleed extends artwork outward past the trim line; safe margin pulls inward from it as a keep-out zone for text and logos. Both use the same math — grow or shrink every side by the same amount — just in opposite directions.
How do I convert millimeters to pixels?
Use px = mm ÷ 25.4 × DPI, then round to the nearest whole pixel. For example, 100 mm at 300 DPI is 100 ÷ 25.4 × 300 = 1181.102…, which rounds to 1181 px.
Does changing DPI change the physical size in millimeters?
No. The millimeter measurement stays the same; DPI only changes how many pixels represent that physical length. Raising the DPI produces more pixels for the same size in mm, while lowering it produces fewer.
How are fractional pixel values rounded?
The tool rounds pixel results to the nearest whole number. It displays millimeters to two decimal places and inches to three decimal places.
What size should a business card artboard be in pixels?
90 × 54 mm — the trim used across Korea and much of Europe — is 1063 × 638 px at 300 DPI, or 1134 × 709 px once a 3 mm bleed is added on every side. A US card is 3.5 × 2 in (88.9 × 50.8 mm), which lands on exactly 1050 × 600 px because 3.5 × 300 and 2 × 300 are whole numbers with nothing to round. Confirm the trim and the bleed with your printer before you build the file — card formats vary more between shops than ISO paper sizes do.
Why is 10 mm 118 px at 300 DPI rather than 120?
Because an inch is 25.4 mm, not 25. The conversion runs 10 ÷ 25.4 × 300 = 118.11, which rounds to 118 px. The gap widens with the measurement: 100 mm is 1181 px rather than 1200, and the 297 mm height of A4 is 3508 px rather than 3564. Any figure worked out by treating an inch as a round 25 mm comes out about 1.6% too large — enough to push artwork past a trim line.
Can I write millimeters straight into CSS instead of converting to pixels?
You can. CSS accepts mm, cm, in, pt and pc, all anchored to the same 96 px per inch, so 10mm resolves to 37.8 px — and inside a print stylesheet those units are the right choice. For anything that ends up as an exported raster, though — an artboard, a canvas element, an image asset — convert to whole pixels at your target DPI instead, since a browser cannot know the physical size of the display it is drawing on.
Should I set the document up in millimeters or in pixels?
It depends on the tool. Illustrator and InDesign work in real-world units and ask for a resolution only when you export, so millimeters are the natural input there. Photoshop, Figma and most screen-first tools want a pixel canvas up front, and Figma has no millimeter unit at all — that is the moment to convert. Settle the output DPI before you create the document, because changing your mind later means rebuilding raster artwork at a different pixel size.