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How to convert a pixel to mm

jaguar123456
jaguar123456 asked
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Last Modified: 2008-03-25
I m working on pdf. I have to get the exact value in millimeter for a pixel for an image. Lets say an image with height 100 pixel and width 200 pixel . What is the conversion formula to convert 100Pixel in millimeter (100 pixel=?millimeter).
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IT Director
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Commented:
This entirely depends on the dpi.

This website has an accurate convertor to use:

http://www.classical-webdesigns.co.uk/resources/pixelinchconvert.html

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b0lsc0ttIT Manager
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Commented:
jaguar123456,

There is no exact, perfect conversion.  The reason is a pixel is a relative measure.  On a screen that uses resolution 800x600 a pixel is larger than one on a screen 1024x768.  To help picture this remember that the actual size of the screen can be the same for both of those settings.

Let me know if you have any questions or need more information.

b0lsc0tt
b0lsc0ttIT Manager
CERTIFIED EXPERT

Commented:
@Wadski - Nice converter!  I remember seeing the formula once but I like that.

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Commented:
if i have an image uploaded in c# by file browse control. How can i get the image width or height in mm instead of picel.
An image file doesn't have any such thing as a measurement in millimetres. You only give it a physical width and height when you print it out, or when you display it on a monitor. Then the width and height depend on PPI (pixels per inch, used on monitors) or DPI (dots per inch, used when printing), and there's no real standard for either. Many high-quality printers will print at 302 DPI, whereas others may go for 150 DPI.

And whereas my monitor is currently running at about 96 PPI, other people may be running their display at 100, or 120, or 80. There's no way of knowing. So there's no sense in talking about the inherent width and height of a digital image in millimetres.

Your dealing with images on a digital page that is designed for printing at specific sizes. So you're being forced to decide how to scale an image to fit on this page. If the person you're working for hasn't given you a DPI to work to, then you need to see what works for you. I recommend sticking to a DPI of at least 150, because any less and the image may look blocky.

Once you know what DPI you're working to, you can work out the conversion like so:

(Physical size in inches) = (Pixel size) divided by (Dots per inch)

Then you need to convert inches to millimetres.
Like b0lsc0tt said, a pixel changes in size depending on your screen resolution. Usually, at optimal monitor resolution 1cm represents 1cm and 1in = 1in.
If I go in Paint under attributs., 1pixel = 0.01inch at my current resolution for my current monitor and 1px = 2.5mm.

You can get nice information from wikipedia. (http://en.wikipedia.org/wiki/Pixel)
Commented:
It's like everybody keeps telling you. The size the image is displayed at depends on the RESULUTION of you screen.

I have a 19" screen with a vertical resolution of 1024 pixels. On this monitor 3 pixels=1mm
On my 15" screen with a vertical resolution of 480 pixels. On this monitor 1.75 pixels=1mm

On my first screen an image with a height of 100 pixels would measure 33 mm
On my second screen the same image would measure 57mm in height.

 

Commented:
I beleive that these poinst should be shared as we all gave the same answer from a slightkly different perspective.
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