Hi,
The number of pixels depends on the DPI (dots per inch) of the picture. You may change the unit that the image is being measured in from pixels to Inches or Centimeters by:
a) Open Paint
b) Open Image
c) Press Alt + F on your keyboard
d) Click Properties
e) Under Units, change to the desired result
The Width and Height can also be edited from the Image Properties window.
Hope the information was helpful