This guide is based on raw elemental content. MEANING: if you came across a magical waterbottle that stored H-Rank Spell energy of your element, you would gain 75%MP rather than 1-3%MP
Note: Eating a spell does not mean it does not cause damage. It simply replenishes MP as you eat it.
A Small Amount, The Size of a Water Bottle: 1-3% Recovery
A Computer Monitor or Kitchen Sink Size Amount: 5% Magic Power
A Spell of Lesser Rank (That Only Uses a Small Amount of your Element): 5% Magic Power
A Bookshelf Size Amount: 10% Magic Power
A Car Sized Amount: 10% Magic Power
A Cannon Blast or Artillery Blast Amount: 10% Magic Power
A Spell of Equal Rank: 10% Magic Power
A Bus Sized Amount: 15% Magic Power
A Spell of Greater Rank: 15% Magic Power
A House Sized Amount: 15% Magic Power
A Lake Sized Amount: 25% Magic Power
A Mall Parking Lot Sized Amount: 25% Magic Power
A Yacht or Cruise Ship Sized Amount: 25% Magic Power
A S-Ranked Spell Effect of your Element: 30% Magic Power
A Mansion or Castle Sized Amount: 50% Magic Power
A Football Field Sized Amount: 50% Magic Power
A Stadium Sized Amount: 50% Magic Power
A Skyscraper Sized Amount: 50% Magic Power
A H-Ranked Spell Effect of your Element: 75% Magic Power
A Meteor or Asteroid Sized Amount: 75% Magic Power
Endless Amount (If Encountered Somehow) for more than 15 Seconds: 100% Magic Power
Moon Sized Amount: 100% Magic Power
NOTE: Light/Darkness Slayers cannot eat more than 10% worth of Light/Darkness per post, unless it it from a spell. The same is with Wind/Sky slayers with air. However when a Sky/Wind slayer eats their element, it does leave them vulnerable to attack as they consume it.
Poison/Venom Slayers must eat acid, or liquid poison to get MP. These are the only slayers than take reduced damage (50%) when eating their element.
TO:
All slayers will gain MP off their respective element based on their power. For example a D-Class Slayer may get more MP from a D-Class spell than an S-Class would get from a D-Class spell. All slayers gain DOUBLE MP to the cost of the spell for the user. For numbers, refer to the Class, Level and Spell Information. Slayers cannot consume a spell that is greater that 2 ranks above them.(A D-Class can consume C-Ranked spells, but not B-Ranked and above spells.) The MP gained from a higher ranked spell is double the cost of a spell their Class.
NOTE: Poison/Venom Slayers must eat acid, or liquid poison to get MP. These are the only slayers than take reduced damage (50%) when eating their element.