Greetings! I am thinking of implementing a weight system into my RPG. Now I'm wondering what kind of a weight unit I should use. First I thought that kilograms would be logical but then again, in a medieval world people probably didn't use kilograms.. and I would probably have a hard time figuring out how much eg. a platemail would weigh in kilograms as I haven't really seen/worn one in real life. I found this list and I'm not quite sure what weight unit is used. What units have you people used and how did you determine how much different items weigh? And it would be nice to hear some tips/ideas for a weight system if you have any. :)

Units are not particularly important, since "10 lb" represents the same amount of weight as "22 kg" or "22,000 g". An item's weight does not change if you switch systems of measurement: the item being measured is the same item in any case.

Therefore, the only concern should be picking a unit of measurement that's convenient. In game design terms, this means picking a unit of measurement that's appropriate for the types of things you'll be dealing with. For instance, in a WW2 strategy game, a unit of nanograms would obviously be a poor choice when listing the weights of tanks and boats. Units of tons would probably be more appropriate.

In general, a good choice for a unit of measurement is one for which most of the equipment/items in your game can be represented in three significant digits or less. This keeps the numbers low and makes comparisons easy. It also helps to set a minimum weight below which you will ignore the weight of items. (For instance, some RPGs set the weight of a gem or a sheet of paper at 0.)

If you're making your own weight system, you can do something like this. Suppose you make up a fictitious unit of weight called the zooble. Ideally, you want everything to weigh between 0.001 and 1000 zoobles. You set the "base" of 1 zooble to be the weight of an apple. Everything should now be compared to the weight of an apple in relative terms. If a dagger weighs twice as much as an apple, then the dagger weighs 2 zoobles; if a scroll weighs one-half as much as an apple, then it weighs 0.5 zoobles.

HTH,
k^2

Good point, but in his case the weight system isn´t really an integral part of the game mechanics - so I think you could sacrifice some accuracy and go for an even slimmer weight representation (no pun intended).
I´d aim for a carry capacity of 80-160 zoobles, depending on the strenght of the character (this lets you have a nice base + strenght modifier, say 50+strenghtmod). Now you don´t really need to track the weight of a single apple, or a bunch of arrows. If you have a slot-based inventory, bulk is a natural limitation (on the people who´d break the system by carrying 10000 apples), so the only interesting items are the really heavy ones. Armor, weapons, treasure.

A much more interesting side of having a weight system is determining encumbrance. However, being bogged down by tons of loot simply isn´t any fun, so if you already have a slot-based inventory there´s probably not that much need to add that sort of stuff.
Ideally, the two would be combined, i.e. particulary heavy inventory items fill up more slots, or take away more inventory slots than they occupy. Easier to visualise, no math involved for the player and less hassle.
For example, the plutonium nugget might only occupy 1 slot in the inventory (since it´s small), but reduce the overall inventory by 8 slots (since it´s damn heavy). You only need some way for the player to see which items are heavy (color-coding might be useful here).

As for determining what weighs how much - do some experimenting, google around for a bit. And since it´s all fictious nobody is going to hold you responsible for getting the weight of a chainmail suit wrong.
(if you go with the above values, a suit of full plate armor would probably weigh 60 zoobles or thereabouts, a longsword might weigh in at 10 zoobles or less)

Thanks for your replies! You've been helpful! It seems that I tried to get "realistic" weight system even though I definately don't need it to be realistic :) Thanks!

To be honest, you don't really need to use a system. For instances, in a weapon's stats, it could say something like:

Attack:
Weight:
Info:

Then, for every ten weight, it would cause your speed to drop your speed by one. Or, the info could say something like, "So heavy, it causes your speed to drop by one," and not even have the weight part.