Levels

 are a game mechanic in Diep.io. Players level up by gaining score, through killing other players or by destroying Polygons. Your total score and level are represented by two bars below your name, as shown on the right. The numbers on the top bar represents your total score whilst the bar compares your score as a percentage of the score of the Leader (the player at the top of the Scoreboard) - as such, when you are the leader, this bar is full. The bottom bar represents your current level, and your current progress to the next level; once this bar is full, you gain a level.

Mechanics
For every level you gain, up to level 28, you get a skill point (after which you get a skill point at level 30, and then every 3 levels afterward up to level 45). Skill points are used to upgrade your Stats. In the skill tree, shown to the right, you can use up to 7 total skill-points for each of 8 stats (except the Smasher branch, which can use up to 10 points, but only 4 stats. The Auto Smasher, however, has all 8 stats with a maximum of 10 points). There are a maximum of 33 skill points, so use them wisely, or the player will end up with an ineffective build.

Even two of the same tanks can vary widely based on how its skill points are distributed; these different skill point distributions are known as Builds. They vary between strict melee builds and ranged builds.

For every 15 levels, up to 45, you may go up to the next Tier, which drastically improves the characteristics of your tank and its Barrels. As you level up:
 * The size of your tank and its ammunition will increase
 * Your tank’s Health will increase by 2 HP per level.
 * Your Field of View (FoV) will increase
 * Your Movement Speed will decrease

Should you die, you will respawn at a lower level, which fully depends on your level before you died. It is usually half of your level, but below Level 12 you will go down only one level, when you are Level 15 you will get Level 12, and upwards to 30 it depends on score, then level.

Experience Gain
Different game modes have different Experience modifiers.
 * FFA, 2 Teams, 4 Teams, Maze and Sandbox has an experience multiplier of x1.
 * Domination has an experience multiplier of x2.
 * Survival, Tag and Mothership has/had an experience multiplier of x3(the Mothership game mode has been removed).

Trivia

 * In old versions of Diep.io (April 15th-17th 2016), the level cap was 60 instead of 45.
 * This meant that tier 5 did in fact exist at one point
 * The only tier 5 tank back then was Octo Tank, when Quad Tank upgraded from Triple Shot.
 * Should you kill someone over 23,536 EXP, you will only receive 23,536 EXP. This may be so that you cannot get 1m points from a player immediately, then it would be unfair since you instantly get the EXP.
 * If you are 20 Levels higher than someone and you kill that opponent, there will be no kill notification. This however only occurs in Free For All or Maze.