The technical name for the metric system is “The International System of Units.”   We abbreviate that to “SI”, from the French “Le Système International d'Unités.”  Nearly all nations in the world use the metric system, and it is the standard in science as well. Below are some common objects, measured using metric units.

Unit

Measure of

Example

gram (g)

mass (“weight”)

one paperclip weighs about 1 g; one nickel weighs 5 g

liter (L)

volume

the largest commonly available soda bottle size is 2 L

milliliter (mL)

volume

one mL of water weighs about as much as a paperclip

meter (m)

length

a doorknob is typically about 1 m above the floor

millimeter (mm)

length

a dime is 1 mm thick

Note: Technically the liter is not an SI unit.  One liter is equal to one cubic decimeter, which is SI-approved.  However, scientists use liters (and milliliters, microliters, etc.) all the time!