How to Resize an Image in CM Free (cm to Pixels)

To resize an image in cm, convert the centimetres to pixels first, because screens and upload forms work in pixels: pixels = cm ÷ 2.54 × DPI. At 300 DPI, a 3.5 × 4.5 cm photo is about 413 × 531 pixels. Crop the photo to that shape, then type those numbers into our free image resizer and download. Nothing is uploaded, and there's no sign-up.

Centimetre sizes come from the paper world: passport photos, ID cards, application forms that will be printed. A digital file has no size in cm until it's printed, so you need to pick how many pixels go into each centimetre. That's what the DPI number does.

The formula, explained

One inch is exactly 2.54 cm. DPI (dots per inch) says how many pixels go into each inch when printed. So:

pixels = cm ÷ 2.54 × DPI

Worked example, 3.5 × 4.5 cm at 300 DPI:

• Width: 3.5 ÷ 2.54 = 1.378 inches; × 300 = 413 pixels
• Height: 4.5 ÷ 2.54 = 1.772 inches; × 300 = 531 pixels

Round to the nearest whole pixel. A pixel either way makes no visible difference.

Ready-made conversions

Size in cm	At 300 DPI	At 200 DPI
2 × 2.5	236 × 295	157 × 197
3 × 4	354 × 472	236 × 315
3.5 × 3.5	413 × 413	276 × 276
3.5 × 4.5	413 × 531	276 × 354
5 × 5	591 × 591	394 × 394
6 × 2 (a signature box, for example)	709 × 236	472 × 157

These are pure conversions, not anyone's official requirement. For what "passport size" means on different forms and in different countries, see passport size photo in cm and pixels.

300 or 200 DPI: which to use?

• The form states a DPI: use that number.
• The form states pixels as well as cm: ignore the cm and use the pixels exactly.
• You'll print it: use 300 DPI. It's the usual standard for sharp photo prints.
• It's only for an online upload with a small KB limit: 200 DPI gives fewer pixels and a smaller file, which makes a tight KB limit easier to hit. It still looks fine on screen.

If you're unsure, 300 DPI is the safer default. You can always compress afterwards. More background in what is DPI.

Step 1: Crop to the right shape

A phone photo is usually 3:4 or 4:3, and 3.5 × 4.5 cm is a slightly different shape. If you resize straight to 413 × 531 with the proportions unlocked, the face gets squashed or stretched. Crop first:

1. Open the free image cropper and choose your photo.
2. Pick Passport 35×45 mm for 3.5 × 4.5 cm (same shape). For other sizes, pick Free and type a width and height in the same proportion, such as 2100 × 2800 for a 3 × 4 cm photo, in the pixel boxes under the picture. Use numbers that fit inside your photo; the resizer shrinks it to the final size next.
3. Drag the box so the head and top of the shoulders are framed as the form describes.
4. Click Crop image and download it as JPG.

Step 2: Resize to the pixel size

1. Open the free image resizer and choose the cropped photo.
2. Keep Pixels selected.
3. Type the width from the table, for example 413. With Lock proportions on, the height fills in at about 531 because you've already cropped to the right shape.
4. If the height is off by a pixel or two and the form demands exact numbers, untick Lock proportions and type the height.
5. Under Save as, choose JPG.
6. Click Resize image. You'll see the result, like 413 × 531 px · 38 KB.
7. Click Download image.

Step 3: Check the KB

Many forms also give a KB range. If your file is too big, run it through the free image compressor as JPG, lowering the quality until the size is inside the range. If it's too small, see how to increase image size in KB.

Printing at the right size

If you're printing the photo yourself, the pixel size alone won't guarantee the paper size, because our resizer doesn't write a DPI value into the file. Printers and print dialogs often scale images to fit the page. Instead:

• In the print dialog, look for options like "actual size" or "100%" rather than "fit to page".
• Or let a photo shop print it; tell them the size in cm.
• To print several copies, many people place them on a 4 × 6 inch layout. Photo print sizes in pixels lists common paper sizes.

Measure one printed copy with a ruler before cutting the rest.

Converting the other way: pixels to cm

To find how big an image will print: cm = pixels ÷ DPI × 2.54. A 1080-pixel-wide image at 300 DPI prints 1080 ÷ 300 × 2.54 = 9.1 cm wide. At 150 DPI it would print twice as wide, but less sharp.

Do it now

Work out the pixels with the formula or the table, crop to the shape, then open the free image resizer and type the numbers. It's free and your photo never leaves your device.