Damage is the basic measure of how vulnerable a character is to the knockback of attacks. At low damages, the character cannot be knocked back very far, and can only be thrown off-stage by the game's most powerful attacks. However, at high damages, attacks deliver considerably more knockback, increasing the risks of severely damaged charcters to be KO'd.
Damage starts at 0% and can rise all the way up to 999%. Though damage is displayed as a percent, getting to 100% does not mean a character is doomed - the number itself is somewhat arbitrary. Damage is measured as an integer in Super Smash Bros. and a decimal number in Melee and Brawl; a damage with a decimal part is rounded down when displayed.
Each attack deals a set amount of damage, which is then modified by things such as Stale-Move Negation before the target is launched. An attack that does no damage will not cause targets to flinch and not produce a regular hit sound, although it will still cause knockback. The damage an attack deals is a significant factor in how much knockback it causes.
The following things are affected by damage:
- Knockback - As a character gets more damage, they fly further when hit. Certain attacks have set knockback, and don't apply.
- Grab time - Characters at high damage can be grabbed for longer periods of time.
- Status time - Generally, characters with higher damage are vulnerable for longer from a status effect (such as sleeping). The exception is being stunned though a shield breaking - the more damage a stunned character has, the faster they can recover.
- Ledge recovery - At 100% and up, a character's ledge animations change, becoming more sluggish and providing more invincibility frames. The slower attack also deals more damage.
- Hoop damage - Characters will not accumulate hoop damage at 150% damage or more.
- Jet Hammer - Like hoop damage, King Dedede will not be damaged by charging this attack when he has 150% or more damage.
- Lucario's attack power - The more damage Lucario has, the more damage his aura-based attacks do. The power is at "normal" when Lucario is at 75%, while it stops decreasing at 20% and caps at 170%.
- Pikmin latch time - Pikmin release a character faster at higher damages.
- A Team Healer's healing power - The more damage the target has, the more damage the item heals.
- Swim time - Higher-damaged characters have less time to swim before panicking, the shortest swim time being at 96% and up.
- Donkey Kong's forward throw - The more damage the grabbed character has, the longer they can be carried, similar to the grab time function.
Should a tournament match time out and the players have equal stock remaining, whoever has less damage is the winner, and a tiebreak procedure is followed should damage also be even.
 Damage meter
The damage meter displays the damage percentage a character has accumulated from attacks, as well as the character's universal symbol and number of stock remaining; unique to Brawl is a display of the character used, and the character's name. In all games, the number of stock remaining is visually represented by the number of icons (the character's mugshot in the original game and Melee, nondescript circles in Brawl); a stock of higher than five is represented by one stock, with a multiplier value next to it; having fifteen stock, for instance, would show "x 15".
Damage meters are displayed at the bottom of the screen during gameplay. While normally opaque, damage meters in Brawl become translucent if a character is "standing" behind it. The damage percentage itself changes colour when more damage is acculumulated; at low percentages, the value is white, but the value gradually turns a darker black (original and Melee) or red (Brawl only) as the value increases.
Additionally, in all three games, the colour of the series symbol behind the damage percentages changes depending on the player's number. Player 1 would receive a red symbol, Player 2 has blue, Player 3 has yellow, and Player 4 has green, while all CPUs have a grey colour; in Brawl, the "underline" underneath the meter would also have a corresponding colour.
- In Melee, when a character reaches 10% or 100% damage, their damage meter displays a leading zero on the frame they get hit. For example, raising one's damage from 7% to 12% will have the meter display 07% for one frame before it changes to 12%.
- In Brawl, the black outline around the damage text is not part of the number textures like in the previous two games; it is instead drawn in real-time.