Photo size in cm, pixels and KB: what each number means
A form asks for "3.5 × 4.5 cm, 20–50 KB, 200 DPI" and you are not sure which number to change. Here is what centimetres, pixels, KB and DPI each measure, how they relate, and how to turn any spec into a file that passes.
Online forms describe the same photo in up to four different ways: centimetres, pixels, kilobytes and DPI. They are not four versions of one number. Each measures something different, and a file has to satisfy all of the ones your form lists.
Once you know what each one means, any spec becomes easy to follow.
The four numbers, in one line each
| The form says | It measures | Where you see it |
|---|---|---|
| 3.5 × 4.5 cm | How big the photo would be printed on paper | Older notices, anything printed |
| 413 × 531 pixels | How many dots the image is made of, across and down | The upload check |
| 20–50 KB | How much space the file takes up | The upload check |
| 200 DPI | How many dots go into each inch when printed | A label stored inside the file |
The upload check almost always looks at pixels and KB. Centimetres and DPI are how a notice describes a printed size, and you turn them into pixels.
From centimetres to pixels
A centimetre on paper becomes a number of pixels once you know the DPI (dots per inch). One inch is 2.54 cm, so:
That is why the DPI matters even though portals rarely check it. The same paper size gives different pixel sizes:
| Size on paper | At 200 DPI | At 300 DPI |
|---|---|---|
| 3.5 × 4.5 cm (common photo) | 276 × 354 pixels | 413 × 531 pixels |
| 3.5 × 1.5 cm (common signature) | 276 × 118 pixels | 413 × 177 pixels |
| 5 × 6 cm (UPPSC photo) | 394 × 472 pixels | 591 × 709 pixels |
If the notice gives centimetres and a DPI, use that DPI. If it gives pixels, ignore the centimetres and use the pixels exactly: that is what the portal checks.
If it gives centimetres alone, there is no single right answer. 200 DPI is common in exam notifications, and 300 DPI is the usual print resolution. Look for a pixel size elsewhere in the notice (often in an annexure table). If there isn't one, ask the helpdesk it lists. The resize tool starts at 300 DPI, so change it if you're working to 200.
Resize by pixels, cm, mm or inchesResize a photo to exact pixel dimensions or centimetres with presets for SSC, IBPS, UPSC, passport and PANKB has nothing to do with centimetres
The file size in KB depends on two things: how many pixels the image has, and how strongly it is compressed.
- More pixels means more KB. A 4000 × 3000 phone photo is several MB. The same photo at 413 × 531 is usually well under 100 KB.
- More compression means fewer KB, but past a point the photo turns blurry and blocky.
So the order matters: first set the pixels, then adjust the KB. Squeezing a full-size phone photo straight down to 20 KB is what produces the smudged photos that get rejected for being unclear.
KB limits are often a range, for example 20–50 KB. A file under the minimum is rejected too. A good compressor looks for the sharpest photo inside the range, and adds size to a file that comes out too small without changing the picture.
Fit a photo into a KB rangeReduce a JPG or PNG to an exact size in KB for exam forms and government portalsDPI is only a label
DPI tells a printer how large to print the image. Changing the DPI label does not change the pixels or the file size, and on screen the photo looks exactly the same.
A few notices, such as UPPSC's and IBPS's, mention a DPI. Very few portals check it. If yours does, set the label and leave the photo alone: re-saving it would change the pixels and KB you already got right.
SFSet the DPI label onlyWrite a 200 or 300 DPI tag into a JPEG or PNG for forms and print shops that ask for itReading a spec, step by step
Take a typical line from a notice: "Photograph: 3.5 cm × 4.5 cm, JPG, 20 KB to 50 KB, 200 DPI."
- Format: JPG. Make sure the file really is a JPEG, not a renamed PNG or an iPhone HEIC photo.
- Pixels: 3.5 × 4.5 cm at 200 DPI → 276 × 354.
- Size: between 20 and 50 KB.
- DPI: set the label to 200. This rarely matters, but costs nothing.
If your exam has a preset, all four are already filled in. If not, enter them yourself.
EPMake a photo from any specMake the photo files for the Any form (custom size) form: Photo 276×354 px, 20–50 KBWidth first, or height first?
Forms write sizes both ways. A photo is almost always taller than it is wide, so of "3.5 × 4.5 cm" and "4.5 × 3.5 cm", the 3.5 is the width. A signature is wider than it is tall. If the finished file looks squashed or stretched, the two numbers are the wrong way round.
Quick answers
The form says 200 × 230 but my photo is 413 × 531. Is bigger fine?
No. Pixel checks are usually exact. Resize to exactly 200 × 230.
The form gives only KB, with no size.
Use a normal passport-size photo (413 × 531 is a safe choice) and bring it into the KB range.
Why does the same photo pass one form and fail another?
Because each form has its own pixels and KB range. Make a separate file for each form, and keep them in clearly named folders.