Weight is a major mechanic of the Pikmin series. Liftable objects weigh some number of carrying units, and in order to carry them, enough Pikmin must be directed to the object in order to support its weight. Some obstacles, such as seesaw blocks, also involve weight.
The weight of objects is measured in arbitrary weight units, with most Pikmin types able to carry exactly 1 weight unit. Smaller objects tend to have lower weights and larger objects tend to have higher weights. Large weights usually come in multiples of 5.
In the main series of Pikmin games, most Pikmin types can carry 1 weight unit, while Purple Pikmin can carry 10 weight units. In Pikmin Bloom, carrying strengths are slightly different – most Pikmin types can still carry 1 weight unit, but Purple Pikmin can carry 5 and Rock Pikmin can carry 3.
In order to carry an object, there must be Pikmin attempting to lift it with a total carrying strength greater than or equal to the object's weight. If there are any less than this, the object will stay put.
Weight is clearly indicated in the HUD, through numbers that appear above the object when Pikmin are carrying or trying to carry it (or when the cursor is placed over it, in Pikmin 3 Deluxe). In Pikmin and Pikmin 2, the top number indicates the weight and the bottom number represents the strength of the Pikmin, to visually symbolize Pikmin lifting the object's weight. In Pikmin 3, the bottom number indicates the weight and the top number represents the strength of the Pikmin, following the convention for writing fractions. In Hey! Pikmin, the same information is indicated through dots that are filled up as Pikmin are thrown onto the object.
Pikmin and leaders
Pikmin and leaders also have weights, and these are used for weight-detecting obstacles. Most Pikmin types weigh 1 unit, except for Purple Pikmin which weigh 10. The weight of a leader is inconsistent and depends on the game and the situation. When a leader lies down, they weigh 4 units in Pikmin and 1 unit in Pikmin 2. When a leader stands on a seesaw block or elevator platform, they weigh 0 units in Pikmin 2 and 1 unit in Pikmin 3. In Pikmin 3, when unconscious leaders are carried at some points in the story, they weigh 5 units.
In Pikmin 2, some treasures dropped by bosses will sometimes change their weight to match the size of the player's squad. This happens if the treasure's weight is greater than the number of Pikmin the player has in the cave when the boss is defeated.
Weight units do not represent a consistent amount of mass. An object's weight is more dependent on its general size and what is needed for gameplay purposes, rather than being based on a real-world weight. There is one treasure that does show its weight, the Doomsday Apparatus, a 1-kilogram dumbbell. It weighs 1000 weight units, indicating that each weight unit is equal to 1 gram, but other treasures in Pikmin 2 easily disprove this; for example, the Proton AA weighs 6 units, while actual AA batteries weigh as much as 25 grams. Thus there is no real-world value of a weight unit.
Weight as an obstacle
Weight is sometimes used in obstacles. Cardboard boxes, paper bags, iron blocks, and iron balls all require a certain number of Pikmin to push on the obstacle in order to pass it, and this pushing strength is measured in weight units, with each Pikmin (and in some cases, each leader) pushing the obstacle with its own weight. Seesaw blocks and elevator platforms use weight in a more complex way, with weight being able to be applied to both sides of a scale.
In Pikmin 2, heavy weights are sometimes used as an obstacle, due to the presence of Purple Pikmin, which can carry 10 units and weigh 10 units themselves. Some treasures weigh more than 100 weight units, and due to the 100 Pikmin limit, Purple Pikmin must be used to carry them because of their increased strength. Some paper bags also take more than the strength of 100 Pikmin to compress, meaning Purple Pikmin are required.
Metric weight in Pikmin Bloom
In Pikmin Bloom, items collectable on expeditions have their weight indicated in grams. This metric weight has nothing to do with the weight of the item in carrying units. For fruits, it indicates how much nectar the fruit will provide. For seedlings and gift boxes, it has no functionality.