Two echoes are better than one, right? Of course!
There's lots of good resources online for this topic, the best of which (I think) are listed below:
https://www.olympus-ims.com/en/applications/measuring-metal-thickness-paint/
https://www.youtube.com/watch?v=zHjmUmJ7VeY
This one has the math to show how the paint magically disappears, so if that's up your alley or you can't sleep, then enjoy!