Pixels to Inches Conversion

As discussed above, converting pixels to inches needs to be done when you have to take a printout of an image or when you have to scan the image. Also, if you enlarge a small pixel image, your image becomes blurred. In this case, you are changing the size of the image more than its resolution , i.e. dimensions of the image expressed in pixels. Hence, we should know the resolution of the image before we change its size.

Pixel
A pixel is the unit of picture. It is used to measure the distinct points captured by a camera. In short, a pixel indicates the number of points on a 2-dimensional grid and is represented by squares or dots.

Inch
An inch is the universal unit of measurement of length. It is mostly used in United Kingdom, Canada and United States. It is denoted by in or a double prime ("). Sometimes inches is written after the desired number.

The size of a printout of an image is measured in inches. As each pixel is varied in size, it is difficult to convert pixel to inch. Also, there is no specific pixels to inches ratio that tells us the pixel to inches conversion of a particular image. Hence, we use the term DPI (Dots Per Inch) or PPI (Pixels Per Inch). They are used to measure the size of each pixel by counting the number of dots (points) captured by the camera.

• DPI - It is a term used to know the printer resolution. It tells us how many dots of ink are present on the printed image.
• PPI - It is a term used to know the image resolution. It tells us the size of the image that a printer will print.

DPI is also sometimes called PPI.

Pixels to Inches Formula
This conversion is done with the help of a formula mentioned below

For Printers	For Scanners
Inches = (Pixels) / (DPI)	Pixels = (Inches) x (DPI)

If you take a file from Adobe Photoshop, photoshop adjusts the image to 72 dpi automatically. Hence we have also used 72 dpi and constructed a pixel to inches table that gives the values from 1" to 10".

Pixels to Inches Table

Pixel	72	108	144	180	216	252	288	324	360	396	432	468	504	540	576	612	648	684	720
Inches	1	1.5	2	2.5	3	3.5	4	4.5	5	5.5	6	6.5	7	7.5	8	8.5	9	9.5	10

Pixel to Inch Conversion Example
Now, let us consider a small example which can help us understand the concept of pixels, inches, DPI and PPI.

For example If you are using a printer that uses 1200 dots of ink per inch and you want to print an image of 600 PPI from it, then each pixel will be made of 4a small dots. Now take a 200 pixel image. This image would be having 800 dots according to our calculation. If you want to take a printout of this image (200 x 200 pixel) and you want to print an image of 50 ppi then you would have a 4" x 4" b image. If you want to print the same image at 25 ppi then you would get an 8" x 8"c image. Formula used a. No. of dots = DPI / PPI (1200 x 1200) DPI / (600 x 600) PPI = 4 1 pixel is equal to no. of dots. Therefore, in this case, 4 dots would be making one pixel. b. Inch = (Pixels) / (PPI) (200 x 200) pixel / (50 x 50) ppi = 4 inches x 4 inches c. Inch = (Pixels) / (PPI) (200 x 200) pixel / (25 x 25) ppi = 8 inches x 8 inches From the above example you can conclude that the number of pixels will remain the same even if you adjust the size of your image.

This conversion is required mostly in printing and image scanning. Since, the image resolution is given in pixels and not inches, it's necessary to use some formula to convert the image without altering its clarity.