Rulers and Scales
Learn
How long is your pencil? How heavy is your backpack? Scientists and everyday people use special tools to answer these questions. Let's learn about rulers and scales!
What is a Ruler?
A ruler is a tool used to measure how long something is. Rulers have marks and numbers that show inches or centimeters. Most rulers are 12 inches long (which equals 1 foot).
What is a Scale?
A scale is a tool used to measure how heavy something is. We measure weight in pounds (lbs) or ounces (oz). When you step on a bathroom scale, it tells you how much you weigh!
How to Use a Ruler
- Place the object at the end of the ruler, starting at 0.
- Make sure the object is straight along the ruler.
- Look at where the object ends.
- Read the number - that is the length!
Units of Length
- Inch (in) - A small unit of length. Your thumb is about 1 inch wide.
- Foot (ft) - 12 inches make 1 foot. A ruler is usually 1 foot long.
- Centimeter (cm) - A metric unit. There are about 2.5 centimeters in 1 inch.
Units of Weight
- Ounce (oz) - A small unit of weight. A slice of bread weighs about 1 ounce.
- Pound (lb) - 16 ounces make 1 pound. A loaf of bread weighs about 1 pound.
Tips for Accurate Measurement
- Always start measuring from 0, not the edge of the ruler.
- Keep your eye level with the measurement to read it correctly.
- When using a scale, make sure it shows 0 before you put anything on it.
Examples
Let's practice measuring with rulers and scales!
Example 1: Measuring a Crayon
What we did: We placed a crayon on a ruler, starting at 0.
What we saw: The crayon ended at the 4-inch mark.
Answer: The crayon is 4 inches long.
Example 2: Measuring a Book
What we did: We measured the length of a book with a ruler.
What we saw: The book went from 0 to 9 inches.
Answer: The book is 9 inches long.
Example 3: Weighing Apples
What we did: We put 3 apples on a scale.
What we saw: The scale showed 1 pound.
Answer: The 3 apples weigh 1 pound together.
Example 4: Comparing Lengths
Object 1: A pencil is 7 inches long.
Object 2: A marker is 5 inches long.
Question: Which is longer? How much longer?
Answer: The pencil is longer. It is 7 - 5 = 2 inches longer than the marker.
Example 5: Converting Feet to Inches
Question: A desk is 3 feet long. How many inches is that?
Remember: 1 foot = 12 inches
Math: 3 x 12 = 36
Answer: The desk is 36 inches long.
Practice
Answer these questions about rulers and scales.
1. What tool do you use to measure how long something is?
Show Answer
A ruler.
2. What tool do you use to measure how heavy something is?
Show Answer
A scale.
3. How many inches are in 1 foot?
Show Answer
12 inches are in 1 foot.
4. A paper clip is 1 inch long. A crayon is 4 inches long. Which is longer?
Show Answer
The crayon is longer (4 inches is more than 1 inch).
5. How many ounces are in 1 pound?
Show Answer
16 ounces are in 1 pound.
6. A string is 2 feet long. How many inches is that?
Show Answer
2 x 12 = 24 inches.
7. You have a ribbon that is 10 inches long. You cut off 3 inches. How long is the ribbon now?
Show Answer
10 - 3 = 7 inches.
8. One apple weighs 5 ounces. Another apple weighs 7 ounces. How much do they weigh together?
Show Answer
5 + 7 = 12 ounces.
9. Where should you start measuring on a ruler?
Show Answer
You should start at 0 (zero), not at the edge of the ruler.
10. Put these lengths in order from shortest to longest: 6 inches, 1 foot, 3 inches
Show Answer
3 inches, 6 inches, 1 foot (Remember: 1 foot = 12 inches, so 1 foot is the longest).
Check Your Understanding
Question 1: What is the difference between a ruler and a scale?
Show Answer
A ruler measures length (how long something is). A scale measures weight (how heavy something is).
Question 2: Why is it important to start measuring at 0 on a ruler?
Show Answer
If you don't start at 0, your measurement will be wrong. You might add extra length that isn't part of what you're measuring.
Question 3: A book is 1 foot long. A notebook is 8 inches long. Which is longer and by how much?
Show Answer
The book is longer. 1 foot = 12 inches. 12 - 8 = 4. The book is 4 inches longer.
Question 4: When would you use a scale instead of a ruler?
Show Answer
You would use a scale when you want to know how heavy something is, like weighing fruit at a store or checking your own weight.
Next Steps
- Practice measuring: Find 5 objects at home and measure them with a ruler. Write down each length.
- Estimate first: Before you measure, guess how long you think something is. Then measure to see how close you were!
- Keep learning: You have completed the Tools and Measurement unit! Continue exploring science to learn more about our world.