When you see a photograph or other image on your computer monitor, you are looking at a rectangle constructed of pixels. A pixel, short for "picture element," is a tiny colored square that your computer mixes with other pixels to create images. DPI refers to the number of pixels per inch in an image. Learning to calculate DPI at various pixel resolutions can help you produce better images when you enlarge or print them.
Press the "Windows" key and "E" together to open Windows Explorer. Navigate to any image file and right-click the file.
Select "View Properties" to open the "Properties" pop-up window. Click the "Details" tab. You will see values for the image's width and height in pixels. For example, the following values may appear in the window:
Width: 440 pixels Height: 254 pixels
Write down those values. These are the image's pixel dimensions. Click "Close" to close the "Properties" window.and return to Windows Explorer.
Right-click the image file. Select "Open With" and then select "Internet Explorer." The image will open in Internet Explorer.
Locate a ruler and measure the image's width and height in inches.
Divide the pixel width that you wrote down by the width in images that you measured to get the image's horizontal DPI. For instance, if the pixel width is 1524 pixels and the width in inches is six, you have this equation:
Horizontal_DPI = 1524 / 6.
Solving for Horizontal_DPI, you get 254 dpi for the image's horizontal resolution.
Divide the image's pixel height by its height in images to determine its vertical DPI.
If you wish to print an image and maintain good quality resolution, choose image dimensions that yield a minimum DPI value of 220 dpi. Do this by using the DPI calculation to compute the dpi for a particular print size. For example, according to the equation, a 4 x 6 print will have a higher DPI value than an 8 x 10 print.