Encumbrance describes the burden that characters and working animals can carry or draw, that in turn impedes how far they can progress with regards to movement and daily travel. How much can be carried determines the character's action points (AP), which are calculated by the character's strength, weight and exceptional capacity. The more that a character and mount attempts to carry, or attempts to pull in the form of a cart or wagon, or even a barge moving along a canal, the fewer AP are made available.
The necessity of tracking encumbrance is a troublesome duty, but no less than would be the actual management of a player character's gear, if such were actually to be stowed away, counted, carefully protected, kept clean or endlessly hunted for when the character can't remember just where the thing was put. Compelling the character to painstakingly count the weight of things helps remind them of what they do possess, and helps establish game strategies where players make plans to reduce their load just prior to combat, or learn to obtain hirelings who can carry most of their stuff, while still being nearby to promptly hand these things over when requested. It's understandable that players dislike the inconvenience inherent in having "stuff." Nevertheless, the DM cannot relent nor show pity for characters who cannot perform simple arithmetic, or learn how to organize their things in a rational, easily added together fashion.
Having separate sheets or files for "person," "backpack," "mule," "hireling" or "home" can greatly simplify a player's life. Turning from the ancient practice of pencil and paper and embracing the newfangled electronic computing equipment that has been readily available for 40 years now is a strategy worth mentioning. If a player complains about the necessity of this, it is the player's misfortune to overcome. DMs do not exist to help players who whine about life sometimes including drudgery.
The determination is accomplished by using a simple excel calculator, which can be located HERE (and then opened with google sheets). Separate tabs for enable calculations for "humanoid" and "cartage," the latter expressing how much an animal or team of animals can pull or carry. Below shows the cell formulas for the humanoid excel sheet. It is quite simple to recreate.
|Penalty per range of weight carried in lbs.|
|None||-1 AP||-2 AP||-3 AP||-4 AP|
|up to 10||11-21||22-32||33-43||44-54|
For example, a halfling weighing 60 lbs., with a strength of 13, inserts those numbers into the boxes for "insert weight" and "insert strength." The result yields the figures shown in the table.
As a humanoid, the character naturally possesses 5 AP. The results show that as long as the halfling only carries up to 10 lbs., no penalty to its movement is felt. However, the next column over, "11-21" (count any fraction above ten as "11") indicates that carrying up to 21 lbs. would reduce the halfling's -1 AP, or "4." The table also shows that the maximum weight the halfling can carry is 54 lbs.