Resize Image in cm
Set a physical size in centimetres and a DPI, and get a photo with exactly the right pixels, under your KB limit.
= 276 × 354 px at 200 DPI. The photo is centre-cropped to this shape and the DPI is written into the JPG.
More options: pixel size, DPI, how KB is counted
Leave width and height empty to let the tool choose. Fill in one of them to keep the proportions; fill in both for an exact size.
From centimetres to pixels
A digital image has no size in centimetres of its own; it only has pixels. A physical size appears when you decide how many pixels go into each inch, the DPI (dots per inch). One inch is exactly 2.54 cm, so:
pixels = centimetres ÷ 2.54 × DPI
For example, 3.5 cm at 300 DPI is 3.5 ÷ 2.54 × 300 = 413.4, rounded to 413 pixels.
Common sizes in pixels
| Size | 150 DPI | 200 DPI | 300 DPI |
|---|---|---|---|
| 2.5 × 3.5 cm | 148 × 207 | 197 × 276 | 295 × 413 |
| 3.5 × 4.5 cm | 207 × 266 | 276 × 354 | 413 × 531 |
| 4 × 5 cm | 236 × 295 | 315 × 394 | 472 × 591 |
| 5.08 × 5.08 cm (2 × 2 in) | 300 × 300 | 400 × 400 | 600 × 600 |
| 10 × 15 cm | 591 × 886 | 787 × 1181 | 1181 × 1772 |
What the tool writes into the file
When you save as JPG, the DPI you enter is stored in the file’s JFIF header, the standard place for pixel density in a JPG. Image viewers, word processors and print dialogs that honour it will show the picture at your chosen physical size. PNG and WebP files from this tool are saved without a DPI value.
Only need pixels? Use the width and height boxes under More options on the KB resizer. Resizing a signature to a box size? The signature resizer also trims margins and whitens the paper.
Frequently asked questions
How do I resize a photo to a size in cm?
Type the width and height in centimetres and the DPI your form or printer asks for. The tool converts that to pixels (cm ÷ 2.54 × DPI), crops the photo to the right shape, saves it under your KB limit and records the DPI in the JPG file.
How many pixels is 3.5 × 4.5 cm?
It depends on the DPI: 276 × 354 pixels at 200 DPI, and 413 × 531 pixels at 300 DPI. The table on this page lists other common sizes.
What DPI should I use?
Use the value your form or print shop specifies. If none is given, focus on the pixel size you need: DPI is only a label in the file, and on screen an image is shown by its pixels.
Does a higher DPI make the file bigger?
Only because it means more pixels. The DPI number itself is just a label in the file header; changing it alone doesn't change the file size or the picture. 3.5 × 4.5 cm at 300 DPI has roughly 2.25 times as many pixels (1.5 × 1.5) as at 200 DPI, so it needs more bytes for the same quality.
My photo is a different shape. Will it be stretched?
No. Choose 'Crop to fill' to trim the excess equally from both sides, or 'Fit with white borders' to keep the whole photo and fill the gap with white. The picture is never distorted.