--- title: "cm to Pixels Calculator – mm, cm, Inches and DPI Both Ways" description: "Convert centimetres, millimetres or inches to pixels at any DPI, and pixels back to a size on paper. For forms, prints and photos. Free, works as you type." url: "https://imagecompressor.si/cm-to-pixels-calculator" lang: "en" --- # Convert cm, mm and inches to pixels Type a size on paper and a DPI to get the pixels, or type pixels to see how large they print. ## How it works 1. **Add your images** Drag and drop, paste, or pick files. They upload over an encrypted connection. 2. **Pick a quality or a target size** Use the quality slider, or tell it exactly how many KB or MB you need. 3. **Download** Save each file, or grab them all at once as a ZIP. Forms and print shops speak in two languages at once. An application asks for a photo of 3.5 by 4.5 centimetres, then for a file in pixels; a printer asks for 300 DPI and a poster of A3. This calculator turns one into the other as you type, both ways, for the width and the height together. The rule behind it is short: pixels equal inches multiplied by DPI, and an inch is 25.4 millimetres. So 3.5 cm at 300 DPI is 3.5 ÷ 2.54 × 300, which rounds to 413 pixels, and 4.5 cm is 531. Going the other way, 600 pixels at 300 DPI print as two inches, or 5.08 cm. Nothing is uploaded on this page; it is arithmetic in your browser. When you have the numbers, the photo maker can crop and size a picture to them. ## Which DPI to use Use the DPI your instructions name. Application portals that convert centimetres to pixels for you usually state it beside the size, most often 200 or 300. Photo labs print at 300. If a form gives only pixels, DPI does not matter for the upload; it only decides how large the picture would print. For screens, the old conventions are 72 DPI on a Mac and 96 on Windows, which is why some forms expect a picture saved at 96. Modern phones and laptops pack two or three times as many pixels into an inch, but the number recorded in a file still follows the old rule. ## Why the pixels are rounded An image cannot hold part of a pixel, so the result is rounded to the nearest whole number, as every program that makes the file does. The difference is at most half a pixel, a fiftieth of a millimetre at 300 DPI, far below what any form or printer can measure. When a form gives a size in pixels and a size in centimetres together, the two only agree at one DPI. Divide the pixels by the centimetres and multiply by 2.54 to find it, or type the pixels on the right and change the DPI until the size on paper matches. ## Common sizes worked out At 300 DPI: 35 × 45 mm is 413 × 531 px; 2 × 2 inches is 600 × 600 px; 5 × 7 cm is 591 × 827 px. At 200 DPI the same 35 × 45 mm photo is 276 × 354 px. A4 paper, 210 × 297 mm, is 2480 × 3508 px at 300 DPI. For signatures, a box of 6 by 2 cm at 200 DPI is 472 by 157 pixels. For a postcard of 15 by 10 cm at 300 DPI you need 1772 by 1181 pixels, close to what a ten-megapixel phone photo already has. ## Frequently asked questions ### How many pixels is one centimetre? It depends on the DPI: about 38 at 96 DPI, 79 at 200 DPI and 118 at 300 DPI. ### How many pixels is an inch? Exactly the DPI: 300 pixels at 300 DPI, 96 at 96 DPI. ### Does changing the DPI change my image? Not its pixels. It changes the print size recorded in the file. Our DPI tool sets it without touching the picture. ### Is anything sent to a server? No. The sums happen in the page as you type. ### Why does my screen show the picture at a different size? Screens ignore DPI and show pixels at their own density, so on-screen size says nothing about print size. ### Is DPI the same as PPI? For a digital picture, yes in practice. PPI, pixels per inch, is the more exact name; forms and printers say DPI for the same number. ### Can I convert a whole document page? Yes: choose millimetres and type the page size, such as 210 by 297 for A4, to see the pixels a scan at that DPI holds. ## Related tools - [Resize a photo for a passport or ID](https://imagecompressor.si/passport-photo-resize): Crop to the photo's shape, get the exact pixels and DPI, and keep the file inside the KB limits your form sets. - [Change an image's DPI](https://imagecompressor.si/change-image-dpi): Record the resolution a form or a print shop asks for, and see how large the picture will print. - [Resize a signature image](https://imagecompressor.si/signature-resize): Type the width, height and KB limits from your form, and get a signature file that fits them.