In GIMP measure the length of the calibration image using the measure tool - set the units to pixels.
Write down the number of pixels.
Now lets say for example, the real size of the calibration image is 5cm, and lets say it measures 650px on screen.
First convert the size into inches, so 5cm = 1.968 inches
The calculation is 650 / 1.968 = 330ppi
In GIMP click Image > Print size > change the PPI to 330ppi
Now if you change the measure tool to cm, and measure it again, it should measure 5cm
Why I am getting larger number at the bottom of the image when i try to measure the distance of a certain part of an image which is less in length and width than the calibration shows in GIMP ?
