Warhammer has several rules (such as outnumbering, fear, etc) where the unit with greater weight of numbers gains an advantage over its opponents. To measure this, each unit has a unit strength. In the case of most infantry units, you just need to count the number of models in the unit for example, 15 Men on foot have a unit strength of - 15 and clearly outnumber eight Elves on foot (unit strength 8).
Models such as cavalry, monsters, war machines, chariots, etc, are individually more powerful than a single man on foot. For example, each cavalry model counts as two infantry. To establish the unit strength of all your different units, you need to use the chart below.
|Model Type||Unit Strength|
|Roughly man-sized; Square 20/25 mm base; On foot||1|
|Up to & including Ogre-sized;* Square 40/50 mm base; On foot||3|
|Monster (larger than Ogre-sized);** Any base/no base||Starting Wounds|
|Cavalry;*** 25 x 50 mm base||2|
|Ridden monsters/chariots||Equal to monster/chariot +1|
|War machines||Equal to the number of crew remaining|
|Units of flyers||1|