The movement speed is influenced by certain items: boots, pets, capes and archery gear. Most of these items have a positive modifier, but some (e.g. piglet) have a negative modifier.
High speed is very helpful when gathering resources but can lead to more accidental attacks by monsters.
The default speed is 0. Max speed is +60 (higher values are possible but are capped to 60).
The total speed determines the time needed to move from one tile to the next.
The formula deduced from the source code is:
<time needed to move to next tile>
= 300ms - <speed> * 3ms
= 3ms * (100 - <speed>)
Therefore the speed is the relative reduction (in %) of the movement time.
|speed||reduction||movement time in ms|
This means that +60 speed is three times as fast as -20 speed!