Length, time, money, standard units
Elementary Foundations • K-5
Measurement is how we describe the size, length, weight, and other properties of objects using numbers and units. Without measurement, we could not build houses, bake cakes, or know when to leave for school. Let's learn the basics!
To measure means to compare something to a standard unit. When you say a table is "3 feet long," you are saying it is as long as 3 rulers placed end to end. Every measurement has two parts:
The number is 7 and the unit is inches.
Length is how long something is from one end to the other. Common units:
| Unit | Abbreviation | About This Long |
|---|---|---|
| Inch | in | Width of a quarter coin |
| Foot | ft | Length of a large ruler (12 inches) |
| Yard | yd | Length of a guitar (3 feet) |
| Centimeter | cm | Width of your pinky fingernail |
| Meter | m | Width of a door (100 centimeters) |
Important: Always start at zero, not at the edge of the ruler (which may not be zero)!
We measure time to know when things happen and how long they take.
| Unit | How Long |
|---|---|
| Second | About one heartbeat |
| Minute | 60 seconds |
| Hour | 60 minutes |
| Day | 24 hours |
| Week | 7 days |
A clock has two hands. The short hand points to the hour. The long hand points to the minutes.
If the short hand is on 3 and the long hand is on 12, the time is 3:00 (three o'clock).
If the short hand is between 3 and 4, and the long hand is on 6, the time is 3:30 (half past three) because 6 on the clock means 30 minutes.
Money has its own units:
| Coin/Bill | Value |
|---|---|
| Penny | 1 cent |
| Nickel | 5 cents |
| Dime | 10 cents |
| Quarter | 25 cents |
| Dollar | 100 cents |
You have 2 quarters, 1 dime, and 3 pennies. How much money is that?
Always include the unit in your answer! Saying "The table is 3" means nothing. Is it 3 inches? 3 feet? 3 meters? Those are very different! A measurement without a unit is incomplete.
Before measuring, always estimate first. Ask yourself, "About how long do I think this is?" This builds your number sense and helps you catch mistakes. If you measure a book and get 200 inches, you know something went wrong -- that would be over 16 feet!
1. Which unit would you use to measure the length of your bedroom: inches, feet, or miles?
Feet. A bedroom is usually about 10-12 feet long. Inches would give a very large number, and miles would be a tiny fraction.
2. How many minutes are in 2 hours?
1 hour = 60 minutes, so 2 hours = 2 x 60 = 120 minutes.
3. You have 3 dimes and 2 nickels. How much money do you have?
3 dimes = 30 cents. 2 nickels = 10 cents. Total: 30 + 10 = 40 cents.
4. A crayon is about 9 cm long. About how many crayons would you need to line up to equal 1 meter (100 cm)?
100 ÷ 9 is about 11 with remainder 1. You would need about 11 crayons.
5. The short hand on a clock is on 7 and the long hand is on 12. What time is it?
7:00 (seven o'clock). The long hand on 12 means zero minutes past the hour.
Summary: Measurement uses numbers and units to describe properties of objects. Length uses inches, feet, centimeters, and meters. Time uses seconds, minutes, and hours. Money uses cents and dollars. Always include your unit, and estimate before you measure.