Oblivion:Encumbrance

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Encumbrance is the load you are carrying. Maximum encumbrance is a derived attribute that determines how much weight you can carry. The total weight of all the items in your inventory must always be less than your maximum encumbrance. Otherwise, you will become over-encumbered and will not be able to move. Grabbed items do not count against your encumbrance. Your maximum encumbrance (without any magic effects applied) is five times your Strength.

Total weight carried (coupled with the type of armor worn and if your equipped weapon is currently sheathed or drawn) affects your Speed. The maximum encumbrance can be temporarily or constantly increased using a Feather or Fortify Strength spell or enchantment. It should be noted that only with Feather will you be able to run faster.

Additionally, your skill level in Heavy Armor or Light Armor will determine the weight of your armor, and by extension, your encumbrance.