KK.2 Choose the appropriate metric unit
What are metric units of measurement?
Metric units are a standardized system used to measure length, mass (often called weight), and volume (capacity). This system is based on multiples of ten, making conversions straightforward.
- The length of a notebook is measured in centimeters.
- The mass of an apple is measured in grams.
- The volume of a water bottle is measured in liters.
The metric system is used by scientists and most countries around the world. It is important to learn because of its logical, decimal-based structure.
Choosing metric units for length
Length is the measurement of how long or short something is. The most common metric units for length are millimeters, centimeters, meters, and kilometers.
- Millimeter (mm): Very small lengths. (The thickness of a coin.)
- Centimeter (cm): Small to medium lengths. (The width of a finger, the height of a book.)
- Meter (m): Medium to large lengths. (The height of a door, the length of a classroom.)
- Kilometer (km): Very long distances. (The distance between two towns.)
A meter is about the same length as a yardstick. A kilometer is a little more than half a mile. Think about the size of the object to select the best unit.
Choosing metric units for mass
Mass is the amount of matter in an object, often thought of as its weight. The most common metric units for mass are grams and kilograms.
- Gram (g): Light masses. (A paperclip, a raisin, a pencil.)
- Kilogram (kg): Heavy masses. (A textbook, a bag of flour, a cat.)
A paperclip has a mass of about one gram. A liter of water has a mass of about one kilogram. One kilogram equals 1,000 grams.
Choosing metric units for volume
Volume (or capacity) is the amount of space a liquid or substance takes up. The most common metric units for volume are milliliters and liters.
- Milliliter (mL): Small volumes. (A spoonful of medicine, a small eye dropper.)
- Liter (L): Large volumes. (A bottle of soda, a large jug of milk.)
A milliliter is a very small amount. A standard water bottle holds about 500 milliliters, and a large juice bottle holds about 2 liters. One liter equals 1,000 milliliters.
Estimating and choosing the best unit
The best metric unit is the one that gives a simple, easy-to-understand number for the object you are measuring—not too large and not too small.
- Would you measure the length of a bus in centimeters or meters?
Answer: Meters. Using centimeters would give a very large, unwieldy number. - Would you measure the mass of a strawberry in grams or kilograms?
Answer: Grams. A kilogram is far too heavy for one strawberry. - Would you measure the volume of soup in a bowl in milliliters or liters?
Answer: Milliliters. Liters are used for much larger containers.
Always ask yourself: "Which unit will give me a number that makes sense without being in the thousands or a tiny fraction?" This helps you choose correctly.