How many pixels is 3.5 x 4.5 cm?

It depends on DPI: about 132 x 170 px at 96 DPI, 276 x 354 px at 200 DPI and 413 x 531 px at 300 DPI.

How many pixels is a 2 x 2 inch photo?

Multiply inches by DPI: 600 x 600 px at 300 DPI, 400 x 400 px at 200 DPI and 192 x 192 px at 96 DPI.

What is the formula to convert cm to pixels?

Pixels = cm divided by 2.54, multiplied by DPI. Round the answer to the nearest whole number.

Does changing DPI reduce file size?

Changing only the DPI label in the file header does not change the pixels, so the file size stays almost the same. Changing the pixel dimensions is what reduces size.

Is DPI the same as PPI?

Strictly, DPI refers to printer ink dots and PPI to image pixels, but in everyday use and in most form notices they mean the same thing.

Pixels, cm, inches and DPI: how to convert photo sizes

Updated 11 October 2026

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Some application notices give photo size in pixels ("200 × 230 pixels"), some in centimetres ("3.5 cm × 4.5 cm") and a few in inches ("2 × 2 inches"). A digital image only really has pixels, so you need a way to translate physical sizes into pixel sizes. That bridge is DPI.

What each unit means

Pixel (px): one tiny square of colour. A digital photo is a grid of pixels, for example 3000 wide by 4000 tall.
Centimetre and inch: physical lengths. 1 inch = 2.54 cm exactly.
DPI (dots per inch) or PPI (pixels per inch): how many pixels are packed into one inch when the image is printed. In casual use the two terms mean the same thing.

A pixel has no fixed physical size on its own. A 600 × 600 px image prints as 2 × 2 inches at 300 DPI, but as 6 × 6 inches at 100 DPI.

The formula

pixels = centimetres ÷ 2.54 × DPI

And for inches: pixels = inches × DPI. Round the result to the nearest whole pixel.

Going the other way: centimetres = pixels ÷ DPI × 2.54.

Worked example

A 3.5 cm wide photo at 300 DPI: 3.5 ÷ 2.54 = 1.378 inches. 1.378 × 300 = 413.4, which rounds to 413 pixels. The 4.5 cm height: 4.5 ÷ 2.54 × 300 = 531.5, which rounds to 531 pixels (the exact value is 531.496, just under the halfway point).

Ready-reckoner table

Physical size	96 DPI	200 DPI	300 DPI
Passport photo 3.5 × 4.5 cm	132 × 170 px	276 × 354 px	413 × 531 px
Square photo 2 × 2 inch (5.08 × 5.08 cm)	192 × 192 px	400 × 400 px	600 × 600 px
Signature 3.5 × 1.5 cm	132 × 57 px	276 × 118 px	413 × 177 px

Notice that the shape (aspect ratio) stays the same at every DPI. Only the number of pixels changes.

Which DPI should you use?

If the notice gives pixel dimensions, use those exactly and ignore DPI.
If the notice gives cm and a DPI (for example "3.5 × 4.5 cm at 200 DPI"), use the formula with that DPI.
If the notice gives only cm with a KB limit, 200 DPI is a sensible middle ground. 300 DPI may push a photo over a small KB limit, and 96 DPI may look blurry when the board prints admit cards.

Our photo resizer and signature resizer accept cm, inches or pixels and do this arithmetic for you.

Does the DPI value inside the file matter?

JPEG files can store a DPI number in their header (the JFIF or EXIF data). This number does not change the pixels at all; it is just a label telling printers what size to print at. A 413 × 531 px photo is the same image whether its header says 72 DPI or 300 DPI, and its file size is practically the same.

Most recruitment and exam portals check only the pixel dimensions, the format and the file size. A few forms, however, state a required DPI, and some document-upload systems read the header value. If your notice mentions DPI, it costs nothing to set the header to match. Our tools write the DPI you choose into the file, so a 3.5 × 4.5 cm photo at 200 DPI is saved as 276 × 354 px with a 200 DPI label.

Common mistakes

Mixing up width and height. Notices usually say width × height, but read carefully. A passport photo is taller than it is wide.
Using the cm figure as pixels. "3.5 × 4.5" means centimetres unless the notice says pixels; a 35 × 45 pixel image would be far too small.
Stretching instead of cropping. If your original photo has a different shape, crop it first. See our guide on aspect ratio.
Upscaling a tiny image. Enlarging a 100 px wide image to 413 px makes it bigger but not sharper.

For specific exam requirements, see the exam-wise photo and signature sizes page and cross-check with the official notice.

Questions people ask

How many pixels is 3.5 x 4.5 cm?: It depends on DPI: about 132 x 170 px at 96 DPI, 276 x 354 px at 200 DPI and 413 x 531 px at 300 DPI.
How many pixels is a 2 x 2 inch photo?: Multiply inches by DPI: 600 x 600 px at 300 DPI, 400 x 400 px at 200 DPI and 192 x 192 px at 96 DPI.
What is the formula to convert cm to pixels?: Pixels = cm divided by 2.54, multiplied by DPI. Round the answer to the nearest whole number.
Does changing DPI reduce file size?: Changing only the DPI label in the file header does not change the pixels, so the file size stays almost the same. Changing the pixel dimensions is what reduces size.
Is DPI the same as PPI?: Strictly, DPI refers to printer ink dots and PPI to image pixels, but in everyday use and in most form notices they mean the same thing.