Characters and creatures are limited in their capacity to carry tools and equipment beyond their natural weight according to their mass and strength.
With regards to player characters, the capacity for movement (both in terms of covering distance and taking actions) is measured in action points. This base movement can be lowered by encumbrance, an expression of the amount of sheer weight which the character (or other creature) carries.
The following downloadable table is designed to calculate a creature's encumbrance in terms of the penalty accrued for carrying a given amount of weight:
The Encumbrance Calculator can be seen HERE.
Use of the table is simple. Some experimentation will show that a halfling character with a weight of 60 lbs. and a strength of 13 has a maximum weight allowance of 55 lbs., while a human with a weight of 180 lbs. and the same strength has a maximum allowance of 165 lbs. A display of the latter should appear as this:
See Fight while Immersed for notes on the effects of moving in water and while swimming on encumbrance calculations.