Bag of holding

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( Bag.png
Name bag of holding
Appearance bag
Base price 100 zm
Weight 15
Material cloth
Monster use Will not be used by monsters.

A bag of holding is one of the most coveted items in NetHack. Placing items into a noncursed bag of holding makes them weigh less, allowing you to carry more items.

The prize at the end of Sokoban always has a 50% chance of being a bag of holding (it will otherwise be an amulet of reflection).

Attempting to remove items from a cursed bag of holding may make them vanish, with a separate 1/13 chance for each item.

When non-greased bags of holding get wet, their contents may get wet. Greasing the bag protects against this, but the grease may wear off. You can also put the bag of holding in a non-cursed oilskin sack to protect it from water damage.

Identification

A bag of holding is easy to identify: first confirm that it isn't a bag of tricks by seeing that you can put items into it, then pick up just enough gear to get encumbered, and put a fair amount of weight into the bag. If you become unencumbered, the bag must be a bag of holding. (One exception: putting gold in a sack or an oilskin sack might change your encumbrance despite the bag not being a bag of holding, because NetHack rounds the weight of your purse and the weight of the gold in your bag separately.)

Price identification can also help to distinguish the various bags: oilskin sacks and bags of tricks cost 100, while normal sacks cost 2. (Make sure there is nothing in the bag when you check the price.) Bags of tricks are also easily identifiable (better to #loot in a shop than to pay a usage fee).

Weight change

The weight of a bag of holding (wgt) - including the 15 for the bag itself - depends on the weight of its contents (cwgt) and its BUC:

blessed:   wgt = 15 + (cwgt/4 + 1)
uncursed:  wgt = 15 + (cwgt/2 + 1)
cursed:    wgt = 15 + cwgt*2

Generally speaking, bags of holding halve the weight of the objects contained, blessed bags divide it by four, and cursed bags double it.

Putting dangerous items into bags of holding

Some items should not be put in a bag of holding as they may make the bag explode, destroying all its contents. These items are:

  • other bags of holding
  • bags of tricks with charges remaining
  • wands of cancellation with charges remaining
  • other bags containing any of the above items (these have a chance of not exploding if you nest them; see below)

The first two are straightforward to avoid; the wand can be trickier. To be safe, do not put any unidentified wands inside the bag that make engravings disappear (this includes cancellation, teleportation, and make invisible).

Strategy

Many players name a plain sack something like "Cancel" or "Don't ever put this in BoH!" and keep what could be wands of cancellation in that sack as a safety measure.

Item management becomes much less tedious if you additionally carry a sack around. Before stashing or unstashing things, you temporarily put your entire main inventory into that sack (escape items, primary weapon, often used tools, etc). Then you won't need to sort all your possessions whether you want them in your bag of holding or in the open. The same technique also helps avoid curses and theft.

Bags of holding are possibly the best candidate in the game for blessing, since doing so doubles the amount you can carry in it.

Due to the risk of explosion, rare items like a wand of wishing or artifacts should probably not be kept in the bag of holding you use for dungeon loot. Any such item that you aren't currently using should probably be kept in a normal or oilskin sack, both to reduce inventory clutter and reduce the risk of destruction by exterior forces (e.g. lightning bolts, trapped boxes, etc).

Consider putting your bag of holding into a sack on lower levels when not in use due to the prevalence of the curse items spell, especially once the Wizard of Yendor starts after you.

If you find a bones pile with a cursed bag of holding, it will likely be too heavy to lift. (If it isn't, you can just pick it up and dip it in holy water, or use a scroll or spell of remove curse.) The best solution is to zap it with a wand or spell of cancellation. This will only uncurse the bag of holding and does not affect its contents. You can also allow a gelatinous cube to eat the bag: the contents, even the organic ones, will land safely on the ground when you kill the cube. Just make sure you can secure all the items before something damages them, since they will be vulnerable to monsters once out of the cube. This destroys the bag of holding, so don't do this if you need it.

If cancellation is not available and the bag is too heavy to lift, you can tip the bag as a last resort. This will still make items vanish, but at least you can get everything else out without being limited by your inventory in how much you can remove.

Nesting bags of holding

It is possible, though risky, to first put items that would ordinarily cause a bag of holding to explode into sacks or oilskin sacks and then place them inside the bag of holding, without causing an explosion.

In general, at most two nested bags of holding are useful because the payload is limited by your ability to lift the innermost bag, not by the outermost weight. You risk an explosion again every time you add contents.

The chance of an explosion occurring then depends on the amount of nesting:[1]

Number of sacks Odds of explosion Success probability
0 1/1 0
1 2/2 0
2 3/4 0.25
3 4/8 0.5
4 5/16 0.6875
5 6/32 0.8125
6 7/64 0.890625
7 8/128 0.9375
8 9/128 0.9296875
n, where n>6 (n+1)/128

If they do not explode, the effect of the two bags will be cumulative, as expected: If both are blessed, any items in the innermost bag will have their weight reduced to about 1/16.

As can be seen in the table above, nesting bags of holding with more than 7 sacks in between makes explosion more likely, so there is no point in using more than 7 sacks.

You may choose to continue to nest the bags of holding further; the chance of success with certain configurations of sacks between the bags of holding is given below:

Number of bags of holding Sack spacing Success probability
2 7 0.9375
3 7,7 0.769042...
4 7,7,7 0.512570...
5 7,7,7,7 0.256222...
6 7,6,6,6,7 0.0935839...
7 7,6,5,5,6,7 0.0236287...
...
43 3,2,2, ... ,2 very small

For example, if you use 7 sacks between each of three bags of holding like this (H for bag of holding, s for sack): HsssssssHsssssssH (denoted as "7,7" in the table above), the chance of successful nesting would be 1-(8/128) for the first nesting, and then (1-(8/128)) * (1-(16/128)) for the second nesting (each of the two 'inner' bags of holding put into the outermost bag must pass its own independent roll for the nesting to succeed[2]) giving roughly a 23.1% chance that something will explode.

Some players either consider the 6.25% chance of explosion from nesting to be an acceptable risk [1] or assume from a test in wizard mode that it is safe. If you are confident you can withstand the explosion, you can risk it before you leave the main dungeon to increase your score or bring specific items to the ascension bar.

References