Pixelcalculator - convert DPI / PPI to pixels and mm, cm, inches

The file remains on your device.

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Result

Pixel total Pixel [ Mpx]
Picture size
dpi / ppi
Color depth
Disk space MB
Pitch μm
Pixel size μm²

sponsored by: Dia Foto Film Scannen www.archivscan.ch 

Formulas for converting DPI - PPI, mm - cm - inches and pixels

Calculation of length or width, pixels and DPI with the following specifications:

Image: 3266×2449 Pixel (8Mpx, 4:3)
Print size: 277 × 207 mm
Pixel density: 300dpi

With these formulas you can convert the length, pixels and DPI / PPI:

\( Length[mm] = {pix × 1 in [25.4mm] \over dpi}\)

\(Pixel = {dpi × mm \over 1 in [25.4mm]}\)

\(dpi = {pix × 1 in [25.4mm] \over mm}\)

\(Bytes = { \over 8 bit [1 Byte]} = {(1000px · 2000px) × 24 \over 8 bit × 1M} = 6MB\)

Examples: print resolution, scan resolution and image size in practice

I want to print a picture for the photo album, 13 x 18 cm, with good quality. How big does the resolution have to be in pixels?

A good quality picture for a photo album is printed at 300 dpi. To calculate the resolution in megapixels, multiply the number of pixels of length and width and divide them by mega (1 million).

\(Pixel X = {300dpi × 13mm \over 25.4mm} = 1535 pix\)

\(Pixel Y = {300dpi × 18mm \over 25.4mm} = 2126 pix\)

\(Resolution = {1535 × 2126 \over 1`000`000} = 3.3 Mpx\)


I have an image with 3264 x 2448 pixels and would like to print it as a poster. How big can I print the poster?

In contrast to a small picture in the photo album, the poster does not have to have a high pixel density, as this is viewed from a greater distance and the pixels become smaller for the eye. Approx. 100 dpi is recommended for a poster.

\(Length = {3264pix × 2.54cm \over 100dpi} = 83 cm\)

\(Width = {2448pix × 2.54cm \over 100dpi} = 62 cm\)


I would like to scan slides and present them with a slide show on the television. Screen TV 40 inches; Resolution: 1,920 x 1,080 pixels. How big does the scan resolution have to be?

The dimensions of a slide are 36 x 24 mm, so the aspect ratio does not match that of the television (television = 16: 9 slide = 3: 2). We only calculate the pixel density of the height of the image, as this is the limiting measure.

\(dpi = {1080pix × 25.4mm \over 24mm} = 1143 dpi\)

Resulting image size horizontally in the correct aspect ratio:

\(pixel = {1143dpi × 36mm \over 25.4mm} = 1620 pixel\)


I would like to print a poster of 900 x 600 mm with the maximum resolution from a slide. How good will the quality be in "dpi"?

The maximum resolution of the scanner is 4000dpi, a slide has the dimensions of 36 x 24 mm. After you have calculated the number of pixels, you can use the dimensions of the poster to calculate the pixel density.

\(Pixel = {4000dpi × 36mm \over 25.4mm} = 5669 Pixel\)

\(dpi = {5669pix × 25.4mm \over 900mm} = 160 dpi\)


Units

engl. unit of length 1 Inch = 25.4 mm
dots per inch 1 dpi = 1 Dot per Inche(25.4 mm)
pixel per inch 1 ppi = 1 Pixel per Inch(25.4 mm)
digital unit of measurement B = Byte
1 bit = 0 | 1
1 B = 8 bit
1 kB = 1024 B
1 MB = 1024 kB