Math sucks; no one enjoys tallying up the individual weights for rope, grapple, lantern, oil, pouches, a dozen potions and scrolls, etc. etc. etc. Looking at the one-handed martial weapons, they're all 4-6 pounds (except, oddly, for rapier). That 1 or 2 pound variance is completely useless and needlessly complex. Every one-handed weapon should instead simply be considered a standard "one-handed weapon" unit of encumbrance.
I propose a simple slot system, similar to the magic item system. This would be simple, and also help players envision their character. Which--by forcing the player to think about what goes where--would make the game more real/fun. Verisimilitude for the win!
For example, a character would have these slots:
- Backpack
- Right hip
- Left hip
- Right shoulder
- Left shoulder
- Belt (for pouches, potions, daggers, spell components, and other small-yet-accessible items)
- Chest (bandolier for throwing daggers and other small items, similar to belt)
- Other (odd spaces created by unique equipment, like boot or wrist dagger sheathes, or double rapier/dagger sheath)
Light weapons can go anywhere. A one-handed weapon can be placed in a hip or shoulder slot. A two handed weapon takes up both shoulder slots. Reach weapons can only be carried: you can't "sheathe" a longspear, after all

. Shields can be carried or slung over a shoulder slot.
Group all items by size, just like how weapons are grouped. Small items (potions, scrolls) can go anywhere. Medium items (rope, lanterns, quivers, rations, spellbooks) can be held, or placed in a backpack, or (for items like waterskins or quivers) occupy a slot. Large or heavy items (chests, block & tackle) have to be carried, worn, or take up multiple "medium" slots in a container like a backpack or satchel. Tiny items (lockpicks, chalk, ink & pen) can fit into pouches.
Containers are considered a certain size, and can fit a number of smaller items. Pouches are considered a small item, and can fit (for example) 8 tiny items. Backpacks are considered a large item, and can fit 8 medium items (including pouches, if needed).
Characters of high or low strength can bear containers that have larger or smaller numbers of slots. So a 10 Str character can carry the default 8 slot backpack, while Conan can carry a big 16 slot backpack. Str also impacts how many slots you can fill; if you're weak you can only have two of the larger weapon slots filled (both hips, or both shoulders, or one of each) while if you're super strong you can even double up on a slot (hang a mace AND a sword off your left hip), though doubling up is awkward and should still impose some sort of penalty (perhaps adding +1 to armor check penalty).
Another way to factor in issues like armor and shields is to simply have each armor have a minimum Str requirement. Light armors require 8 Str, medium armors 10 Str, and heavy armors 12 Str. Same for shields: light shields require 8 Str, heavy shields require 10 Str, and tower shields require 12 Str. Why so low? Because common soldiers with average stats need to be able to use normal weapons and armor.
