How large an image on computer scxreen?

Although Trekkeruss has given you an answer of sorts it is basically meaningless. You can't apply a measurement in inches that will have an real meaning in relation to a digital image on computer. Just because the supposed size when viewed on your monitor is equal to 40x30 inches that doesn't tell you anything meaningful. Look at it on a different monitor with a greater or lesser pixel density and the supposed size would be different and neither would have any real world meaning.

I think you might get more useful information if you explain why you want to know the size in inches for a digital file. What is it you are trying to achieve?

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Dan
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I love my girlfriend, my dog and my canon 5DIII - even though none of them ever do what I tell them
I am learning photo graphee - see the results at www.danmarchant.com