How to count the amount of pixels an object in a photograph takes up

Question

I have been trying to find out the distance of an of object from an image using this calculator https://www.scantips.com/lights/subjectdistance.html

But I need to know how many pixels long the object is. How do I do this?

Answer 1

Because you want to see the height and width of a object you can use for example XnView MP.

Open the image, press and hold left button of the mouse and mark the object. On the bottom right part of the screen you will see the dimensions in pixels of the marked area.

Answer 2

Basically you have to use some kind of photo editor, in most of them (even MS Paint) marking part that interest you will show you the dimensions somewhere.

If your options are limited (e.g. you are on your smartphone) you can also use cropping function and see dimensions of cropped image in its details (just make sure that your cropping method doesn't enlarge photo - you can crop half of your image first and check if one dimension changed by about half. Also remember to save the cropped image as a new copy)

If you want to calculate a dimension that isn't parallel to your photo frame, just calculate it with Pythagorean theorem or use some diagonal calculator online using two dimensions acquired by previous methods.

Good luck :)