App that can '''measure'' a line on a pic

[snowdog]

Hello,

I'm looking for an app like paint but then that can measure a line if you draw it, eg. so you can apply a scale to it.

So far with straight horizontal or vertical lines I did this by reading the pixels the line started at and ended at, but obv. this is a bit hard ( well hard, I'm too lazy actually) to use on lines that aren't perfectly vertical or horizontal ( yes I can use maths, Pythagoras, but surely an app can do this for me lol ? ).

So kind of like on google earth the measuring tool, you draw a line and it measures the distance, but then for a picture.

Anyone knows such an app ?

 

[snowdog]

Okay thank you seems to work .
Bit iffy to control the app as pasting ( ctrl + v) an image in your clipboard doesnt seem to work but that aside it works and i know how to use *** measure tool, thank you.

Reason I need it is I need to calculate how much force ( in newtons) there is onto the cables of the Erasmusbridge. I have the scematics of it and I know how much upward force there is needed in the point where the cables are attached to the roadway and I need to translate that into force on the cables wich are in various angles. And for that I have to scale stuff on the scematic eg 1cm or 10 pixels is 1 newton...

Anyways enough rubbish talk, I just need to do something for school and you helped me, ty .