Influence Point

Influence Points, or IP, are a measure of a summoner's influence in the League of Legends rewarded based on their performance on the Fields of Justice. The amount of IP rewarded varies on the outcome of the game, the game type, and the length of the match. Influence points can be used to permanently unlock champions, runes, or additional runebook pages in the Riot Store.

Determining Factors
Since patch V1.0.0.111, the amount of Influence Points awarded for a given match depends on these rules:
 * It increases linearly with the duration of the game.
 * For each Field of Justice there is a floor and cap for IP gained per match.
 * Games longer than the cap or shorter than the floor grant the same IP as a game with length corresponding to the length of the cap.
 * The floor does not apply to Co-op vs. AI games, the cap is not tested.
 * On Summoner's Rift these lower and upper limits are at 25 minutes (76 IP for a win) and 55 minutes (145 IP for a win).
 * On Twisted Treeline the floor is at 20 minutes (64 IP for a win) and the cap is at 55 minutes (145 IP for a win).
 * The precise limits for the Crystal Scar are not known, the floor seems to be around 10 minutes, additional testing is needed. It was previously believed to be 20 minutes as surrender is available at 15 minutes similar to the Twisted Treeline.
 * The cap is different on ranked games. IP boost grants 168 IP on ranked games on Summoner's Rift, so it appears the cap is 65 minutes for ranked games on Summoner's Rift.
 * For a win, the reward is approximately: 18 IP + 2.312 per minute IP.
 * For a loss, the reward is approximately: 16 IP + 1.405 per minute IP.
 * An active Wins IP Boost gives you a flat amount of IP equivalent to the minimum IP you could get from a game matching the duration of the cap (for whichever game mode you are playing).
 * A custom game has a penalty of 25%.
 * Custom games only grant IP when teams are balanced. (example: 2vs2, NOT 2vs3)
 * Co-op vs. AI and custom games have separate limit timers which reset daily, after 180 minutes for Co-op vs. AI and 120 minutes for custom games no IP is earned.
 * Twisted Treeline in Co-op vs. AI does not have a limit timer.
 * A win, in any game type except custom, will award the "First Win of the Day" bonus if available. This bonus is a fixed 150 IP which is not affected by boosts or penalties. When awarded, this bonus becomes unavailable for 22 hours.

Co-op vs AI Gamemode Modifiers
Co-op vs. AI matches have penalties depending on the summoner level and difficulty.
 * The rule for minimum IP reward does not apply (a match shorter than 25 minutes will give less IP than a match of 25 minutes).
 * The rule for maximum IP reward does apply.

General
Formula: { [base IP] + ([IP / min] * [game time in minutes]) * [gamemode modifier] } + [Dominion Bonus]

The game time is always rounded down, meaning a game of 35:59 grants the same amount as a 35:00 minute game.

Dominion has a special bonus that is given depending on how well your team did. The more hp your nexus has if you win the larger the bonus, the less hp their nexus has if you lose the larger your bonus.

The custom game modifier is 0.75.

You will earn 0 XP/IP when playing a custom game that does not have the same number of champions on both teams.

Prices
For a table listing the IP prices of all the champions, please see here.

For a table listing the IP prices of all runes, please see here.

Trivia

 * Runes can only be bought with IP.
 * Skins and bundles can be bought only with RP, not with IP.
 * The maximum/minium amount of IP  from a match is:
 * Win: (first win of the day bonus, 55+ mins ranked match, IP boost (timed and per win)) 150 + 168 + 168 + 168 = 654 IP (822 on a double-IP weekend)
 * Loss (55+ mins match): 95 IP