Encumbrance rating

Version 0.31: This article may not be up to date for the latest stable release of Crawl.

For shield encumbrance, see Shields. Not to be confused with encumbrance from inventory weight, an obsolete mechanic.

An encumbrance rating is a penalty applied to body armour. The heavier your armour, the higher the encumbrance rating. The higher the encumbrance, the higher the penalty is to evasion, spellcasting, stealth, and ranged weapons. Encumbrance can be mitigated, but not removed, by strength and Armour skill.

This page exclusively covers body armour. Certain other armours may "encumber" you, but use different mechanics.

• Bardings have a -2 EV penalty. This does not penalize casting, stealth, etc., and cannot be reduced by strength / armour skill.
• Shields also have an encumbrance rating, but it's handled entirely differently. See Shields for more details.

See the Table of Armours for numerical details on all items with encumbrance ratings.

Base Penalty

Body armour has a "base" penalty of:

Where:

• "S" = scale. Scale essentially equals to 1 (100/100), meaning it has no impact the final result. It is used to increase the precision of encumbrance calculations.
• "armour" = Armour skill and "str" = strength.

This equation can be simplified into the following form:

While this equation is not used directly, it is used to determine most of the other penalties.

Evasion

Encumbrance rating has two effects on EV:

1. Encumbrance will directly lower your evasion. This is reduced by armour skill and strength.
2. Encumbrance will lower the effect of Dodging skill on evasion. This penalty is only reduced by strength.

EV Penalty

Encumbrance will lower your EV by:

This number is subtracted directly from your EV score.

Dodging Penalty

Encumbrance will also reduce the EV gained by Dodging skill and dexterity.

For Dodging Bonus = (8 + 0.8 × Dodging × Dex) / (20 - size_factor). See Evasion for more detail.

This Dodging Bonus is then multiplied by a modifier:

For e = encumbrance. If (e-3) is 0 or lower, then there's no penalty to Dodging.

Spellcasting Penalty

Encumbrance increases "spellFailure", which is not to be confused with your chance of actually failing a spell:

As a reference:

• 1 intelligence = -2 spellFailure
• 1 Spellcasting skill = -3 spellFailure
• 1 (Spell School) skill = -12 spellFailure, divided by the number of schools of a spell

"SpellFailure" is then transformed multiple times to determine your actual chance of failure. See spell success for details.

Stealth Penalty

Encumbrance reduces your stealth score:

Independent of armour skill or strength. This does not reduce the Stealth skill, so encumbrance doesn't impact the strength of stabs, nor does it impact the use of atropa and datura darts.

Ranged Weapon Penalty

Encumbrance slows down Ranged Weapons (but not Throwing weapons). It increases the attack delay of these weapons, in units of decaAut:

This penalty is rounded to the tenths place in a weighted fashion, then added to your attack delay. Note that, because these are in units of decaAut, the equation is divided by 10. If you want regular aut, multiply by 10.

Analysis

In general:

• Armour skill has a linear impact on encumbrance. Every point in Armour reduces encumbrance by -2.2%.
• Strength has a logarithmic impact - i.e. a diminishing return - on encumbrance. For everything except the Dodging penalty, going from 7 -> 17 strength will give the same % reduction as 2 -> 7 strength, which has the same reduction as 17 -> 37 strength.

On Evasion

As mentioned above, strength has a diminishing return on encumbrance as a whole. But there exists a clear breakpoint, e - 3 = str, where the dodging penalty shifts from 1 equation to another. Beyond this point, strength starts to drop more rapidly. This breakpoint only applies to Dodging, not to casting or the general EV penalty.

This is the basis behind a rule of thumb, where strength should at least be the same number as encumbrance. However, this is not a hard rule. More strength is still likely to have a noticeable impact. And, if you don't have any Dodging skill, then str = (e-3) has next-to-no significance to your character.

The % of Dodging Bonus is tabulated below, as an example:

Fire dragon scales (e=11)				Plate armour (e=18)
Strength	% of Dodging	Delta		Strength	% of Dodging	Delta
5	31.25%			12	40.0%
6	37.5%	+6.25%		13	43.3%	+3.3%
7	43.75%	+6.25%		14	46.6%	+3.3%
8	50%	+6.25%		15	50%	+3.3%
9	55.5%	+5.5%		16	53.1%	+3.1%
10	60%	+4.5%		17	55.9%	+2.8%
11	63.6%	+3.6%		18	58.3%	+2.4%

Note, again, that this is only the impact on Dodging bonus. Remember that there is another EV penalty on top of this. Overall, every point of strength will give less EV than the previous point of strength. (Of course, you should still have high strength if you plan to wear heavy armour).

On Spellcasting

Armour skill vs Spell skill

• Encumbrance increases SpellFailure by 19/225 * encumbrance^2 * (90 - 2armour) / (str+3). This can be rearranged to -armour * 38/225 * encumbrance^2 / (str+3).
• Having 1 of every spell school (except Spellcasting) reduces SpellFailure by 12. Divide by number of spell schools if needed.
• Therefore, each level in Armour is worth 19/1350 * encumbrance^2 / (str+3), or roughly 1/71 * encumbrance^2 / (str+3), levels in each spell school.

For example, if you have 11 strength and fire dragon scales, 1 Armour skill = 1/71 * 11^2 / 14 = 0.122 levels in each spell school. This is a ratio of 8.21 Armour skill : 1 in each spell school. If you have a dual-school spell, like Iron Shot, 4.1 Armour skill = 1 Earth Magic OR 1 Conjurations, while 8.21 Armour = 1 Earth AND Conjurations.

Of course, this analysis does NOT include the fact that Armour increases your AC and EV. You may want to train Armour for those reasons, or train spell schools to increase power.

Strength vs Intelligence

• For a given change in strength 'x', strength reduces SpellFailure by (1/<str+3> - 1/<str+x+3>) * 19/225 * encumbrance^2 * (90 - 2armour).
• Intelligence reduces SpellFailure by 2 per point.

For example, you have 11 strength, fire dragon scales, and 0 Armour skill. On level up, you have a choice of 2 str or 2 int. The impact of +2 str is equal to (1/14 - 1/16) * 19/225 * 11^2 * 90 = 8.21 SpellFailure, greater than 2*2 = 4 SpellFailure from intelligence.

Of course, intelligence also increases spell power, while strength also reduces shield encumbrance.

Spreadsheet

See this spreadsheet (and/or make a copy) for an armour penalty calculator: Calculator (outdated as of 0.27)

History

• Ranged weapon penalties were added in 0.29.
• Armour to-hit penalties 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.