Creatures come in a variety of sizes. Generally, humans--and most other heroes in Secret Wars have a have a size of 5, or Medium. Exceptions are as follows:
Horrors start with a base size of 3
A nezumi's rat-form is size 3
Dwarves and gnomes start with a base size of 4
A kitsune's fox-form and a size 4
Trolls start with a base size of 6
A bersarkir's bear-form is size 7
Here are some common sizes:
1 - Tiny: Handheld objects, rodents, pixies
2 - Infant humans, cats, skateboards
3 - Small: mid-sized dog, child, window, closet monsters
4 - Teenage human, spear, chair
5 - Medium: Adult human, door, wolf, leopard
7 - Deer, bicycles
9 - Large: Alligator, bear, coffin
11 - Vault door, compact car, horse
13 - Huge: Great white shark, pickup truck
15 - Full-sized SUV, elephant. young dragon
20 - Light airplane, yacht, semi-truck
25 - Gargantuan: Dump truck, houseboat, tour bus, mature dragon
30 - Small house, whale
40 - Large house
50 - Colossal: Jumbo jet, elder wyrm
60 - Apartment building
80 - Big box store
100 - Skyscraper, stadium, shopping mall
Bulk measures how unwieldy an object is to carry, representing its size, weight and general awkwardness. Usually, an item or person has a Bulk Value equal to its size score, but unwieldy items usually have a higher bulk. Living, conscious creatures usually have a bulk one higher than their size due to their constant flailing.
Items can have a standard bulk modifier, or they can be considered Light (L) or negligible (-). For example, a knife or a smartphone has a value of Light, while a pen or credit card has a value of negligible. Ten light items count as 1 bulk (rounding down fractions), while items of negligible bulk only count when you're trying to carry a ludicrous amount.
A character's Bulk Limit is equal to 5+their Strength modifier. A character carrying more than that is encumbered. A character cannot physically carry more than 10+their strength modifier.
If you're dragging something, you can count its bulk as half of its normal value. You can only drag one thing at a time, and you must use both hands to do so. If you're dragging in combat (such as dragging an unconscious ally behind cover), costs 3 actions, and you can move, at most, 1 range during that round.