There are a fair number of good alternatives out there, but none of them quite feel right to me. So I made my own.
Item classifications and their meaningsOnce you're on the road, items come in two main categories: Small items, and Large items. What category an object falls into is a combination of weight, bulk, and how much care must be taken with that object in trasport. It's important to note that this only matters for new items you pick up, since you're using your previously-calculated encumbrance as your starting point.
Small ItemsSmall items don't weigh you down. Some common examples of small items include swords, scrolls, potions, cloaks, very small rugs, helmets, and spellbooks. 100 coins also count as a Small item in my game.
Five Small items count as one Large item.
Large ItemsIf you are carrying a Large item, count yourself one step more encumbered. If you are carrying 2 Large items, count yourself two steps more encumbered, and take a -2 to hit and AC. Also, you aren't going to be stealthy. You cannot normally carry more than 2 Large items. Examples of Large items include plate or chain mail, shields, tapestries, small treasure chests, busts, and Halfling bodies.
Free ItemsAnything not big enough to be a small item basically doesn't count against encumbrance. This includes rings, jewels, certain other jewelry (often assuming you're wearing it), lockpicks, and generally anything that would easily fit in the palm of your hand and not feel terribly weighty.
Two-man ItemsThe name's pretty much self-explanatory; these things require at least two adventurers to cooperate to move them. Two-man items count as two Large items for each member of the moving team. Examples include large chests, armoires, and elf-sized statues.
|Another example of a large item|
Extensions and VariationsThe core works pretty well all by itself. People I've played with have agreed that it hits the sweet spot between complexity and plausibility, allowing them to actually make meaningful choices about what they'll carry while not feeling like it takes too much time and effort. However, over time I've identified some tweaks I like to make to differentiate characters and some further rulings I've made that help the system feel more complete.
StrengthCharacters with a Strength of 5 or less can only carry one Large item, and for them it behaves as though they are carrying two. (Two encumbrance levels, minuses in combat.) Characters with a Strength of 15 or higher can carry an extra Large item before being doubly encumbered. Characters with the rare and coveted 18 Strength can carry two more.
RaceDwarves can carry one extra Large item before being doubly encumbered, because dwarves are naturally doughty. (Woe betide the dungeon denizens who run across a Dwarf with 18 Strength; they'll all be naked.)
Halflings on the other hand can carry one fewer, because they're tiny.
Elves are roughly human-sized, but slightly smaller. Some items that would count as Small for a Man might count as Large for them, and they only get four Small items to the Large (unless you forget or don't care).
Load Bearing Equipment and Beasts of Burden
Ponies and donkeys can carry three Large items. Horses can carry five. Mules can carry six. Good luck fitting a mule in a dungeon. Other more fantastic animals are up to the GM.
Bags come in two different sizes. Small bags can carry up to 3 Small items, combining them to count as one. Large bags can carry up to 10 Small items, counting as 1 Large item. Small chests are the same, but you don't have to worry about your bundle of swords accidentally cutting through it while you're running away from goblins.
Medium chests can carry up to 25 Small items, but they count as 2 Large items. (You can share this load between 2 people if you can't carry enough, and this allows you to easily drop it in combat.)
Large chests are Two-man items, and can carry up to 50 Small items.
A hand-cart or wheelbarrow will allow you to carry 50 Small items by yourself, but of course you aren't going to be stealthy and you aren't doing anything else with your hands.
Potion belts, scroll belts, and the like carry 5 or so of the specified Small items and count the total as just one Small item.
Magical load-bearing equipment such as Tenkar's Flying Disc and Bags of Holding should be similarly rated by the GM for how many Small items they can carry. (I like calling Bags of Holding Large items that can carry up to 200 Small items.)
Once you get to wagons and the like, you've grown beyond the limits where this system is useful.
Use your judgment on what to allow players to put in bags. Just because a glaive is a Large item doesn't mean it'll fit into your large bag.
Parting ThoughtsI like this system because I find it easy to run at table and easy for players to understand. It doesn't require looking things up, ever. I also think that, because of the ease of use in play, it opens up inventory management as a real object that can be manipulated in play. For example, a cursed Loadstone is two Large objects that cannot be put down. Further, temporary effects can really, actually be useful or debilitating in play without requiring a mood-crippling amount of number fiddling. As proof, below I'll share two spells that have made it onto the Cleric list in my game.
Share the Load
Duration: 1d4 + cleric level hours
This spell allows the subject to carry one more Large item before experiencing any encumbrance effects. Only works on humanoids.
Burden of Truth
Range: 30 ft
Duration: 1d4 + cleric level turns
This spell causes the subject to feel the extra heft of 2 more Large items. Save vs. magic to resist.