How Many Pixels Is a 3 × 4 cm Photo?
Convert a 3 × 4 cm print into pixels at 300 or 600 DPI and distinguish physical photo sizes from digital upload dimensions.
By Nexurivo · Updated
There is no single pixel answer without resolution
Three by four centimeters describes a physical rectangle, not one fixed digital file size. It is the same as 30 × 40 millimeters and has a 3:4 aspect ratio. To calculate pixels, you also need the intended print resolution. At 300 DPI the rounded output is 354 × 472 pixels; at 600 DPI it is 709 × 945 pixels. Neither value by itself establishes that a photograph meets an application authority's requirements.
Work through the conversion
Use pixels = millimeters ÷ 25.4 × DPI for each side. At 300 DPI, the width calculation is 30 ÷ 25.4 × 300 = 354.33, rounded to 354. The height is 40 ÷ 25.4 × 300 = 472.44, rounded to 472. At 600 DPI the unrounded results are approximately 708.66 and 944.88. Small rounding differences are expected. They should not be confused with an incorrect aspect ratio or a print dialog that scales the entire page.
Prepare a proportional crop
Choose Photo 3 × 4 and select a portrait with enough space around the subject. Adjust the crop to the intended composition rather than stretching the source. A square original can fit inside a 3:4 frame with padding or be cropped to fill it, but those choices produce different borders and framing. Review the destination's background and positioning rules before choosing. Extra pixels from a high DPI setting do not fix a poor crop or an out-of-focus face.
Treat digital requirements separately
An online form might request a 300 × 400 pixel image. That shares a 3:4 ratio, but it is not the same pixel output as a 3 × 4 cm print at 300 DPI. This is an example, not a standard for any country or institution. Use Online Form Image Maker when a destination specifies pixels and a byte ceiling together. Follow its accepted file formats as well. A correctly sized print image may still be unsuitable for that digital upload.
Measure before producing all copies
For a paper submission, export the photo or arrange it on the desired sheet. In the print application, choose the matching paper dimensions and Actual Size. Disable automatic fitting and check whether the printer adds margins or borderless enlargement. Measure a test print with a ruler before cutting multiple copies. A 3 × 4 label addresses physical size only; review current instructions for head placement, expression, background and all other acceptance conditions with the requesting authority.