Forms ask for image dimensions in three different languages. Upload portals talk in pixels: "200 × 230 px". Print jobs talk in centimetres or inches: "3.5 × 4.5 cm". And somewhere in between, someone asks for a JPG when what you have is a PNG.
All three are the same operation — changing the size and format of an image — and doing it properly takes about twenty seconds.
Pixels, centimetres and the number that connects them
An image file stores pixels. It does not store a physical size. The bridge between the two is DPI — dots per inch — which says how many pixels get packed into each inch of paper.
The arithmetic is simple:
- pixels = inches × DPI
- inches = centimetres ÷ 2.54
So a 3.5 × 4.5 cm photo at 300 DPI needs about 413 × 531 pixels. At 72 DPI the same physical size would need only 99 × 128 pixels — and would print looking soft and pixellated.
| Purpose | Use | Why |
|---|---|---|
| Printing | 300 DPI | The standard for sharp photo and document printing |
| Large posters | 150 DPI | Viewed from a distance, so fewer pixels per inch is fine |
| Screen and web | 72–96 DPI | DPI barely matters on screen; the pixel count is what counts |
How to resize an image
- Open the Resize / Convert Image tool.
- Upload the photo.
- Enter the width and height you need.
- Leave keep aspect ratio on unless you deliberately want to stretch the image.
- Choose the output format — JPG or PNG — and download.
Resize to exact dimensions and convert between JPG and PNG — free.
Open the Resize / Convert toolWhy "keep aspect ratio" matters
The aspect ratio is the relationship between width and height. Force a 4:3 photo into a square box and faces get visibly squashed — it is one of the most obvious signs of a hurried job.
When a form demands dimensions that do not match your photo's shape, do not stretch it. Crop to the right shape first, then resize. The Auto Crop Scanner can crop to a chosen shape, and for headshots the Passport Photo Maker handles the framing for you.
Enlarging does not add detail
Making an image smaller throws pixels away and looks fine. Making it bigger has to invent pixels that were never captured, and invented pixels look soft and mushy — no tool can recover detail that the camera did not record.
So if a form wants at least 1000 pixels wide and your image is 400, do not upscale it. Go back to the original photo, or retake it. Always work from the largest version you have.
JPG or PNG?
- JPG — photographs, faces, scenery, anything with smooth colour. Small files, no transparency.
- PNG — screenshots, logos, line art, anything with hard edges or transparency. Larger files, perfectly crisp.
Converting PNG to JPG will flatten any transparency onto a solid background. Converting JPG to PNG does not undo compression damage that is already baked in — it just stores the same picture in a bigger file.
Frequently asked questions
How do I convert cm to pixels?
Divide the centimetres by 2.54 to get inches, then multiply by your DPI. For print, use 300. Example: 3.5 cm ÷ 2.54 × 300 ≈ 413 pixels.
Will resizing reduce the file size?
Yes, considerably — fewer pixels means a smaller file. If you have a specific KB target to hit, follow up with Compress Image.
Can I resize several images at once?
This tool handles one image at a time so you can check each result. For a batch of photos going into a single document, Image to PDF takes several files together.
My resized photo looks blurry.
Almost always because it was enlarged past its real resolution. Check the original's pixel dimensions — if they are smaller than what you asked for, the softness is unavoidable.
Does resizing rotate my photo?
No. If your photo appears sideways, that is the camera's orientation tag. Use the Auto Crop Scanner, which has rotate controls, to fix it.
Related tools
- Compress Image — hit an exact KB limit after resizing.
- Auto Crop Scanner — crop and straighten before you resize.
- AI Background Remover — plain background for application photos.
- Image to PDF — deliver the finished image as a PDF.