Units used in ARK are based on the Unreal engine's units, which are approximately 1 cm.
They are what is being displayed on the Bed's Fast-Traveling map, and what is shown in many stats in this Wiki.

A foundation in ARK is about 300x300 units, i.e. 3x3m

Creatures' travel speeds are only shown as percentages in-game, so in order to calculate a real speed from that, one would have to look up the absolute speed on this Wiki, apply any upgrade factor, and would then be able to calculate an approximate travel time (useful when trying to figure out whether the ride across some extreme cold area might be too long).
For example, if my Pteranodon's speed factor is 135%, and I see on the creature's stats table that its base sprint speed is ~ 1,898, that means its absolute speed is 2,562 (1,898*1.35=2,562). Now, if the distance from one bed to another shown as 400,000 units, I can divide the distance by the calculated speed, and will conclude that it will take about 150 seconds to get from one bed to another (400,000/2562=156). So - if your ride has enough stamina to sprint for 150 seconds, you should be fine!