Not to be confused with encumbrance from inventory weight, an obsolete mechanic.
An encumbrance rating is a penalty applied by almost all body armour and bardings. This is a measure of how much your defensive equipment gets in the way of spellcasting, ranged weapons, and attempts to evade enemy attacks. Multiple sources of encumbrance rating stack with each other. Shields also have a penalty, but it is handled differently and is never actually named in game (see Shields#Shield Penalties).
In general, the heavier your equipment, the greater the encumbrance rating will be. You can reduce the impact of your encumbrance rating by increasing your strength or Armour, though the stealth penalty is always constant. For the purposes of evasion, there is a breakpoint at (ER-2) strength, where reaching this point provides the greatest gain per specific strength point, with strength having a slowly diminishing return from there.
See the Table of Armours for numerical details on all items with encumbrance ratings.
See this spreadsheet (and/or make a copy) for an armour penalty calculator: Calculator
Adjusted body armour penalty
Where e is the encumbrance rating of the armour, S is an arbitrary scale the base is used at for the particular penalty, a is the armour skill of the subject, and s is the strength of the subject.
This penalty is not applied directly, rather it is used in evasion, to hit, and cast chance. For to hit the scale used is 20, while for evasion and cast the scale used is 100. This syntax is the same for the other formula.
Adjusted evasion penalty
This amount is subtracted from your evasion along with other factors such as your size and dodge skill before being stepped down.
Where B is the base dodge bonus (formula shown), S is the relationship between strength and encumbrance, d is dodge skill, D is dexterity stepped down if it is above 24, and F is normalized size factor.
This penalty along with the evasion penalty impacts your ability to evade attacks. Due to the change of function when encumbrance nears strength, this penalty makes it a good idea to have a strength equal to or larger than two minus the encumbrance of the armour.
The size factor is normalized around medium size, and can be derived from the following table:
|Medium: Most Races||0|
|Large: Troll, Ogre, Palentonga, Naga||-1|
This penalty is subtracted from your stealth score.
If this added to your shield penalty is positive, then this is added to your failure chance. See spell success for more information.
Ranged Weapon Penalty
[ (e)^2 / 2250 ] * [ (90-2a) / (S + 3) ]
This penalty, in decaAut, is added onto weapon delay to Ranged Weapons, but not Throwing.
Encumbrance Penalty Analysis
By calculating the second derivative of the dodge penalty plus the evasion penalty (formula shown above), we can measure the gains from additional strength for any given character. Using this information we can determine what value you would want to raise your strength to for the greatest benefit. The graph on the right shows a spike in gains from strength at two lower than the encumbrance rating of the armour, however a few points after that spike tend to be fairly beneficial as well.
This relationship leads to the rule of thumb for strength that you should at least raise it to the same number as your encumbrance, though more strength is still likely to have a noticeable impact. This rule of thumb does not apply to Spellcasting and Ranged Weapons usage, only for EV.
- Ranged weapon penalities were added in 0.29.
- Armour to-hit penalities were removed in 0.28. Specifically, they were:
- Armour no longer slows down unarmed melee attacks, and some of the mathematics have changed between 0.13 and 0.17.
- Encumbrance ratings were introduced in 0.13, replacing the EV penalty system.