Speed

is one of the eleven core player statistics. It is a measure of the walking and running speed of the player expressed as a percentage of the original speed. Interestingly, speed will not apply while jumping.

Any item that increases speed by a base value (such as +40) can be thought of as an increase of the base speed by that much percentage.

It is capped at 400% under normal circumstances, but this cap can be increased to 600%. High speed is very hard to reach under normal circumstances. Most methods of reaching 400% speed require the Rogue Sword, or armor such as the Obsidian Chestplate, Farmer Boots, and Young Dragon Armor, or buffs.

Increasing Base Speed
Players have a base of 100 by default. It can be increased by:
 * Turning in Fairy Souls to Tia the Fairy
 * Leveling Wolf Slayer
 * Holding more Accessories

Increasing Bonus Speed
There are several ways to gain additional bonus, which last for various amounts of time.

Increasing Maximum Speed
Players have a maximum of 400% by default. It can be increased by: Note that both abilities apply and the player's maximum speed can be extended to 600%, but appears not to with the popular mod SkyBlock Addons made by Biscuit, as it only supports up to 500% speed. Inspecting the SkyBlock Menu's profile will correctly display the speed.
 * Young Dragon Armor's Full Set ability
 * A Black Cat Pet's first ability

Decreasing
A mob's speed stat can be worsened in a handful of ways. A Slowness Potion decreases speed by the same intervals as speed potions. The Venomous Potion decreases speed by 5% per level up to 20%.

Players may use Rancher's Boots to cap their speed at a lower value, used notably to farm efficiently without skipping crops from too much speed outpacing the block breaking speed.

Achieving Maximum Speed
To achieve 600%, the player must first use a full set of Young Dragon Armor and a Level 100 Black Cat Pet. This increased the speed cap to 600% and also gives 80% (150% when above 50% ). The Black Cat Pet gives 25% and can hold a Spooky Cupcake that gives 20%. The pet also gives 100, which can be used with some item abilities to increase. The total for just the armor and pet is 105%, and when above 50% , 175%. The player already has 100% base speed, which brings the total to 275% when above 50%. 194 Fairy Souls and LVL 8 Wolf Slayer both give 3% base. Sugar Rush III on boots gives 6%. The enchantment Legion V can also be used to increase your speed around other players by up to 56% if you have it on every armor piece. Talisman Spamming can give a large amount of speed when reforged to Vivid. Here is a list of all Accessories and their  bonus when reforged to Vivid. Using all of these Accessories (other than accessories that have a higher tier) with a Vivid reforge gives approximately 207. This brings the total to 494. Holding a Yeti Rod that has caught at least 1000 fish increases by 100%. This will total up to 594%, which means only a few of the Accessories need to be Recombobulated to achieve 600%. However, to use all 600%, the player must be above 50% and be holding their Yeti Rod.

Speed in B/s
Movement speed in blocks per second can be easily calculated using this formula:

$$Movement Speed = Base Speed * Speed Modifier$$ Base Speed - amount of movement speed coded into Minecraft. Base Speed values for different actions are following: Speed Modifier - your Speed stat value. Percent value must be converted to decimal (e.x. 230% = 2.3).

Example

 * Information
 * Action: Sprinting
 * Speed value: 207%
 * Calculation

$$5.6 * 2.07 = 11.592 B/s$$

Trivia

 * There used to be a bug where the speed buff from the Aspect of the End never ran out on the player's island. This allowed for the player to easily achieve 400% speed. This was patched in version 0.7.
 * Riding on a Level 1 Skeleton Horse Pet is equivalent to walking with 200% speed (8.62 B/s).
 * Riding on a Level 100 Skeleton Horse Pet is equivalent to walking with 500% speed (21.55 B/s).

Video
速度