Item Weight

Item weights are represented in Strength units. For example, an item of 18 weight units requires a bare minimum of 18 strength points for you to carry without suffering an encumbrance penalty on your TU refresh rate.

Therefore, if you want to micromanage your items for a very weak soldier, add up the weight of all the items you want to issue the soldier, then compare the result against the soldier's strength. Add or remove items as necessary while keeping the weight vs. strength level balanced.

Tip: All small items (one inventory square) are 3 weight units.

Item weights are a heavy influencing factor for determining throwing distance. Note that although ammo loaded into a weapon does count towards soldier encumbrance, its weight is ignored when throwing the weapon.

In the battlescape display, an item lying on the ground might represent a pile of items. In this case, it is the heaviest item displayed (usually a corpse).

The following represents a complete list of item weights for X-Com UFO Defense/Enemy Unknown. TFTD item weight list to follow.

Pistol..................5 
 Pistol Clip............3
Rifle...................8
 Rifle Clip.............3 
Heavy Cannon...........18
 HC-AP..................6
 HC-HE..................6
 HC-IN..................6
Auto Cannon............19
 AC-AP..................5
 AC-HE..................5
 AC-IN..................5
Rocket Launcher........10
 Small Rocket...........6
 Large Rocket...........8
 Incendiary Rocket......8

Laser Pistol............7
Laser Rifle............10
Heavy Laser............18

Heavy Plasma............8
  Heavy Plasma Clip.....3
Plasma Rifle............5
  Plasma Rifle Clip.....3
Plasma Pistol...........3
  Plasma Pistol Clip....3
Blaster Launcher.......16
  Blaster Bomb..........3
Small Launcher.........10
  Stun Bomb.............3
 
Stun Rod................6 

Grenade.................3
Smoke Grenade...........3
Proximity Grenade.......3
High Explosive..........6
Alien Grenade...........3
Electro Flare...........3 

Motion Scanner..........3
Medi-Kit................5
Psi-Amp................10
Mind Probe..............5
Elerium.................3

Corpses:
Jumpsuit...............22
Personal Armor.........24
Power/Flying Armor.....26 
Sectoid................30
Snakeman...............40
Ethereal...............25
Muton..................40
Floater................20
Celatid................35
Silacoid...............40
Chryssalid.............40

Quick Reference for common item sets

Loaded Rifle + 3 one-space items*...........20

Laser Rifle + 3 one-space items.............19

Loaded Heavy Cannon.........................24
   + extra clip.............................30

Loaded Auto Cannon..........................24
   + extra clip.............................29

Loaded Rocket Launcher + 3 Large Rockets....42
   w/ all Small Rockets.....................34

Loaded Heavy Plasma + 3 one-space items.....20

Loaded Blaster Launcher.....................19
   + 5 Blaster Bombs........................34

Loaded Small Launcher + 2 one-space items...19

Supplementary items:
   Laser Pistol..............................7
   Loaded Plasma Pistol......................6
   Stun Rod..................................6
   Mind Probe................................5
   Psi-Amp..................................10 

* All one space items (grenades, ammo clips, motion scanner, stun bombs) have a weight of 3.

Uncarryable items

The remaining items cannot be picked up, but are included for completeness sake: 

Corpses (continued): 
Reaper*................50
Cyberdisc*.............50
Sectopod*..............50
Hovertank*.............50
Tank*..................50
Male Civilian..........30
Female Civilian........50 

* That's 50 for each quarter

Unused Items*: 
Unused slot**...........1   
Unused slot............22 (Same as above, but heavier)
Unused slot............22 (Ditto) 
Unused slot.............1  (Appears to be a type of plasma clip) 
Unused slot.............4 (Pistol variant. Slower, less accurate, 1x1 in size)
Unused slot.............4 (Unknown)

*The game has six unused item slots. Unfortunately, there's no known way to get them 
 into any of the item transfer screens. Otherwise, they'd make six extra weapons, clips,
 or grenades, but the bullets fired would look like a tank/cannon round, they won't have
 proper labels, and they won't have Ufopaedia entries. They can be added to the Skyranger
 with a ship store editor, and they'll appear in combat, but their obdata.dat entries have
 to be tweaked so that they work.

**The first three unused slots are an unnamed multi-barrelled laser. 
  Prime attracting feature: 15% TU Autofire @ 50% accuracy with 40 laser damage
 
Note: In TFTD, the above slots are used by the gauss clips and the drills

Sorted by item weight

Here's an alternate listing sorted by Item Weight. Does not include items that can't be picked up:

Weight Item

 3   Alien Grenade
     Blaster Bomb
     Electro Flare
     Elerium
     Grenade
     Heavy Plasma Clip
     Motion Scanner
     Pistol Clip
     Plasma Pistol
     Plasma Pistol Clip
     Plasma Rifle Clip
     Proximity Grenade
     Rifle Clip
     Smoke Grenade
     Stun Bomb

 5   AC-AP
     AC-HE
     AC-IN
     Medi-Kit
     Mind Probe
     Pistol
     Plasma Rifle

 6   HC-AP
     HC-HE
     HC-IN
     High Explosive
     Small Rocket
     Stun Rod

 7   Laser Pistol

 8   Heavy Plasma
     Incendiary Rocket
     Large Rocket
     Rifle

10   Laser Rifle
     Psi-Amp
     Rocket Launcher
     Small Launcher

16   Blaster Launcher

18   Heavy Cannon
     Heavy Laser

19   Auto Cannon

20   Floater

22   Soldier in Jumpsuit

24   Soldier in Personal Armor

25   Ethereal

26   Soldier in Power or Flying Armor

30   Sectoid

35   Celatid

40   Chryssalid
     Muton
     Silacoid
     Snakeman