Many people have some videos that are unedited, show little if any refraction and unmeasureable curvature over water at distances of 23 miles or so.
There are formulas for this, and it is miles squared x 8 inches.
THe measurements of our 'world' are off...none of the scientits care....which means nothing to me....but, I wonder how many people realize this.
"unedited" on YouTube means diddley squat. Modern video editing programs allow all sorts of editing without it being obvious.
The earth of course is not a sphere, but a spheroid - with some areas thanks to the bulge in the middle being significantly larger than others. Any rule of thumb for the curvature is just that - a rule of thumb, and not exact.
That the curvature is real is shown by looking over any large body of water, and observing how tall masted boats appear - first the top of the masts appear, then gradually more and more of the boats.
That the overall size of the Earth is known is shown - as others have pointed out - by the distances planes fly and the shortest directions they fly.
I don't trust those YouTube or other uploaded videos - because they contradict a huge number of independently sourced data points. It would take literally hundreds of thousands of people hiding info for zero reason for the paranoics to be correct. It would also require many corporations to waste many millions of dollars a year to support those lies. Ridiculous.
Some formulas people use are just rules of thumb - but even then they are close enough for everyday use.