In-Game Falling Death Data
On the page, for falling damage on the official Guild Wars 2 wiki, we can find a nice little graphic that shows how much %-health you lose respectively to which height you fall from. Due to copyright, I can't post it here so I have to describe it. It shows the %-health loss in a step of 10 starting from 0% and going to 180% and the distance in in-game units with a step of 100 going from 0 to 1500. It marks anything starting with 1500 as deadly even with fall damage reduction trade and 1250 units or higher as deadly without falling damage trait.[1]
Conversion
A long time ago I already did a conversion from units to meters and feet. I'll leave this link to the post so you can check on it if you don't remember.
The conversion was 1 Unit is equal to 2.52cm or 0.083ft.
Now we just have to put in the numbers and do the calculation...
a) with falling damage reduction: 1500units * 2.52cm/unit = 3780cm or 37.8m.For feet it's 1500units * 0.083ft/unit = 124.5ft
b) without falling damage reduction: 1250units * 2.52cm/unit = 31.5m.For feet it's 1250units * 0.083ft/unit = 103.75ft
Well... that sounds ridiculous. I don't have anything to compare it to though. So let's see for a real-life equivalent to compare.
Most Reliable Resource
Looking through the interwebs there are a lot of stories about huge falls and indecisiveness of accurate numbers. Though according to a paper of NASA the fatal speed seems to be 16m/s on hard surfaces.[2] Assuming the acceleration due to gravitation a to be 9.81m/s² and the formula being V = a * t. The total time of the fall would be t = V / a, thereby 16m/s / 9.81m/s² = 1.63s.
To calculate the distance of the fall we have to put this into the following formula: d = 1/2 * g * t²
Thus our falling distance is 1/2 * 9.81m/s² * (1.63s)² = 13.03m. (14.75ft)
Can We Calculate the Gravity on Tyria?
To do that we would need to know how long it takes to fall a certain distance or how long it takes to fall 1250, additionally it wouldn't be accurate enough compared to simply calculating the falling speed and acceleration between reaching two points during a free fall.
Nonetheless, it's still interesting to see that it takes twice the height in Guild Wars 2 to die compared to real life. Float away Sapient Beings, float away!
[1] https://wiki.guildwars2.com/wiki/Damage#Falling_damage
[2] https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930020462.pdf