Carry That Weight
This mod is designed to make inventory capacity more interesting, believable, and configurable. There are several other mods that do similar things (discussed below), but I made this one because I was running three mods to try to achieve the balance I wanted and I was still not completely satisfied. My main goals were

• Make inventory capacity about more than just hauling more loot: limit inventory space, but reward looters for high stamina.
• Avoid sharp transitions that are triggered by picking up items, and more-or-less preserve the vanilla over-encumbered mechanic.
• Incorporate some reasonable volumetric considerations to inventory management without being too complicated.
• Make everything configurable, but not overwhelmingly so.
  

Features
All features are configurable in the MCM (see screenshots). By default, everything is disabled.
Configure capacity formula
The formula is:

capacity = (Base Capacity) + Level * (Per Level Capacity) + Stamina * (Per Stamina Capacity)


In vanilla, the parameters are:

(Base Capacity) = 150, (Per Level Capacity) = 0, and (Per Stamina Capacity) = 0.5

Now you can change these three parameters to whatever you like. Changes will apply retroactively. Keep capacity low if you like hard-core inventory management, or make stamina more valuable using encumbrance buffs (described further down). Enchantments, potions, and spells still work as you would expect.
Soft-cap item limiter
Set soft-caps on the number of various items in your inventory. As you exceed these limits, your pack gradually becomes messier and less efficient, decreasing its effective capacity by a configurable penalty for each item past the limit. This soft-cap system prevents sudden severe penalties; being shot with an arrow when you have a full quiver is not a debilitating debuff.

There are 6 item categories:

• Quiver: arrows and bolts
• Satchel: potions and poisons
• Coin Purse: vanilla coin
• Pouches: small items (weight < 0.9, including weightless items, but not gold)
• Bags: medium items (0.9 <= weight < 9)
• Affixed Items: large items (weight >= 9) and shields
  

Equipped armor does not count toward the limits. Your current number of items in each category and the corresponding caps are displayed in the effects window. You can set the strength of this penalty per category. Set it very high if you want the soft cap to be more like a hard cap, or set it to zero to disable the limiter for that category.

As and example,  if the arrow limit is set to 30 with a penalty of 5, but you have 50 arrows in your inventory, then the 20 arrows above the limit each reduce your carry capacity by 5, for a total reduction of 100.
Encumbrance buffs and debuffs
In vanilla, unused carry capacity is irrelevant -- an almost full pack is the same as an empty one. This mod aims to fix that and to make unfilled capacity more useful. You can choose to have your unused capacity affect your stamina, speed, or stealth, or any combination of these. You can choose a buff for when your pack is below a certain fraction of its capacity, and a debuff for when it's above a certain fraction of its capacity. The buff linearly transitions into the debuff between the capacity thresholds.

Example: In the Stat Modifier Settings MCM screenshot, my movement speed is buffed or debuffed by up to 30 percent depending on how full my inventory is. My stamina and sneak skill linearly decrease by between 0 and 30 points whenever my pack is more than 45% full. With these settings if my pack is at 75% capacity, I'm getting a 16 point penalty to sneak and stamina and a 15% speed penalty. If my pack is at 25% capacity, I'm getting a 15% speed boost and no penalties. These numbers are displayed with charming descriptions in the effects menu.
Miscellaneous maintenance settings
In the maintenance tab of the MCM, you can enable or disable the mod, force override your base encumbrance (if it was affected by another mod), configure how often your inventory is checked for changes, and configure how often (if ever) notifications alerting you that you've exceeded your soft caps will appear.

Compatibility
No or minor issues:
Should be compatible with almost all mods, including other encumbrance-related ones (although features will overlap). For example, if you like my limiter system, but want more granular control over encumbrance buffs and debuffs, you can disable my buffs and debuffs and run my mod alongside Cobb Encumbrance.

Mods that add a constant modifier to your inventory capacity can be offset by adjusting the "Base Capacity" slider in the MCM.
Major issues:
Mods that frequently and directly alter the player's base capacity are unlikely to function properly alongside this mod. Examples inclue Realistic Capacity and Requiem.

Additionally, playing Enderal as a lycanthrope may cause incorrect carry weight values right before and after transformation, as it uses a custom carry weight script.

Performance and Accuracy
Inventory accounting is inherently inefficient in Skyrim, and inventory limiters are notorious for loosing count and/or being very script-heavy. I mitigate this by making event scripting do most of the heavy lifting, but with players routinely adding and removing large numbers of items very quickly (e.g., via "take all"), Skyrim's poor old scripting engine is bound to fall behind eventually. The scripts should know when they have fallen too far behind and will pause, then do a complete recount of items when things quiet down. In addition, the mod does a periodic "sanity check" (every 300 seconds by default, but this is configurable in the Maintenance tab of the MCM). In my testing, I have not noticed any performance decrease or miscounting of limited items; however, the displayed numbers do not update while the menu is open; if they seem off, close and reopen the menu.

Alternative / Complementary Mods
Obviously, I think my mod is the best capacity mod, but that's because it's tailor made for me. You -- and I know this will come as a great disappointment -- are not me. If you're looking for some capacity-related mods, here are some you might like more than this one.

• Cobb Encumbrance: a very detailed and highly configurable encumbrance buff and debuff system. You can define up to ten "stages" of encumbrance in which different buffs or debuffs are applied. Here, I've opted for a simpler linear interpolation buffing/debuffing method and fewer possible buffs. You can use Carry That Weight with Cobb Encumbrance; the buffs and debuffs will stack as appropriate.
• RAB Inventory Limits: a "hard cap" inventory limiter. It has more inventory categories, and when you exceed the limits, you drop items. This mechanic can cause some problems with mods that add a bunch of items to the player for short periods, although patches are available. This can be used together with Carry That Weight if you don't like my soft caps, or you want a combination of hard and soft caps. The item categories are not necessarily in agreement.
• Hardcore Capacity: another "hard cap" limiter. When you exceed the cap, you become over-encumbered. This also works on followers, but I've noticed it often loses count and doesn't work on all followers. It's also annoying to become over-encumbered when you get hit with an arrow. As with RAB Inventory Limits, Hardcore Capacity can be used with Carry That Weight if you really want to.
• Realistic Capacity: drastically decreases your inventory capacity, but dynamically adds it back based on equipped armor and recently used weapons. I really like this approach, but I have noticed that the numbers are sometimes not properly calculated. I have not tested this with Carry That Weight, but I strongly suspect they are incompatible.
• Potions and Lockpick Limiter and Arrow Limiter: Two light-weight hard-cap limiter mods by the same author.
• Backpack Containers (Oldrim): makes campfire backpacks into placeable containers. Works with only minor issues in SE (converting the esp's form version is recommended). Carry That Weight does not detect the items stored inside the backpack, so it's a bit of a cheat, but the backpack's weight adjusts to its contents. A great way to keep your inventory organized.
• Various backpack and pouch mods: carry weight enchantments work as you'd expect. You can set a lower base capacity to offset their bonuses if you think they're too strong.
  

Installing/Uninstalling
Install as usual. Uninstalling is not supported, but if you want to uninstall anyway, disable the mod in the MCM and exit the menu first.