Measurement Units: How They Compare

Grade 4 Measurement and Data: 4.MD.A.1

In this lesson:

• Compare unit sizes using "times as" language
• Convert a larger unit into a smaller one
• Build and use two-column conversion tables

Learning Objectives for This Lesson

By the end of today, you can:

1. State the key metric and customary conversion factors
2. Describe a unit relationship as a "times as" comparison
3. Convert a larger unit to a smaller unit
4. Generate a conversion table and describe its pattern
5. Apply conversion to real-world problems

How Many Tiles Match One Ruler?

Here's a foot ruler and a stack of one-inch tiles.

How many tiles would you need to line up, end to end, to match the ruler exactly?

Quick Check: How Many Times As Many?

Recall from earlier: if you have 3 marbles and a friend has 12, your friend has ___ times as many as you.

Hold that phrase — "times as many" — in mind. We're about to use it a lot.

Counting Tiles Gives Us the Rule

1 foot = 12 inches

Twelve Times as Long, Not Twelve More

• 1 foot is 12 times as long as 1 inch, not "12 more"
• The larger unit (foot) is built from smaller units (inches)
• The conversion factor, 12, is fixed and never changes
• It tells how many small units fit inside one large unit

Eight Facts You Need to Know

Every fact here is a "times as" statement, grouped by what it measures.

Predict First: True or False?

"1 meter is 10 times as long as 1 centimeter."

Decide before advancing — is this true or false?

Match Every Pair to Its Factor

• 1 km and 1 m → ___
• 1 kg and 1 g → ___
• 1 L and 1 mL → ___
• 1 ft and 1 in → ___
• 1 hr and 1 min → ___

Fill in each blank, then check against the reference chart.

From Comparing Sizes to Converting

You can now compare any two units in a system — a foot to an inch, a kilogram
to a gram.

But comparing isn't the same as converting. What if you have an actual
measurement and need it in different units?

The Snake Problem: Feet to Inches

4 × 12 = 48 inches

Predict: 15 Inches or 36 Inches?

A different snake is 3 feet long.

Is that 3 + 12 = 15 inches, or 3 x 12 = 36 inches? Pick one before advancing.

Multiply the Groups, Don't Add Them

3 feet = 3 groups of 12 inches, not one 12 added on.

The general method: find the conversion factor, then multiply.

Two More Conversions, Same One Rule

A table is 2 meters long. How many centimeters?

A bag of rice weighs 3 kilograms. How many grams?

When a Measurement Has Two Units

A class period is 1 hour and 15 minutes long. How many minutes is that in total?

Convert only the larger unit, then add the leftover:

The Answer Should Always Get Bigger

Converting to a smaller unit always produces a bigger number.

Does 5 kilograms equal 0.005 grams? Does that seem reasonable — is a gram
bigger or smaller than a kilogram?

Your Turn: Two Hours Thirty Minutes

A movie is 2 hours and 30 minutes long. How many minutes is that in total?

Step 1: Convert the hour part: 1 hr = 60 min, so 2 hr = ?
Step 2: Add the leftover 30 minutes.

From One Conversion to a Whole Table

You can now convert any single measurement you're handed.

What if, instead of one conversion at a time, we organized every possible one
into a single table — so the whole pattern was visible at once?

Building the Feet and Inches Table

If 1 foot is 12 inches, how many inches are in 2 feet? In 5 feet?

Two Patterns, One Multiplication Rule

• Across the columns: multiply the number of feet by 12
• Down the inches column: the values increase by 12 each row
• The down-column pattern isn't a separate fact — each new row adds one more group of 12

Build Your Own Hours and Minutes Table

Generate a table for hours and minutes, from 1 hour up to 5 hours.

State the across-column rule and the down-column pattern for your table.

Metric shortcut: a factor of 1,000 just means appending three zeros.

Table Check: How Tall Is the Shelf?

A bookshelf is 3 feet tall. Using the table above, how many inches tall is that?

What If the Table Runs Out?

Now: a different bookshelf is 7 feet tall. Your table only goes up to 5 feet.

Extend the table, or compute directly:

Now Mix Every Measurement Type Together

You can convert a single measurement and generate a table for any unit pair.

Today's last stretch mixes every measurement type — length, weight, capacity,
and time — using both of those skills together.

Rapid Fire: Name Every Conversion Factor

For each pair, state the conversion factor and the "times as" comparison:

km and m · m and cm · kg and g · L and mL · ft and in · lb and oz · hr and min · min and sec

Five Problems, Five Measurement Systems

• 7 ft jump rope, x12, 84 in
• 6 kg watermelon, x1,000, 6,000 g
• 45-min soccer half, x60, 2,700 sec
• 15 L fish tank, x1,000, 15,000 mL
• 4 lb package, x16, 64 oz

Build a Table, Then Go Further

Build a minutes-and-seconds table from 1 to 5 minutes.

Then use it to find: how many seconds are in 3 minutes and 20 seconds?

Your Turn, No Help This Time

A track workout lasts 2 hours. How many seconds is that in total?

No factor is given. No table is drawn. Work the entire conversion yourself.

Four Mistakes to Watch Out For

3 groups of 12, not 12 added once: 2 ft is 24 in, not 14 in
Smaller unit means bigger number: always multiply, never divide
Meters to centimeters uses 100, not the usual 1,000
48 inches and 4 feet are the same length, different units

Key Takeaways From Today's Lesson

✓ A conversion factor is a fixed multiplication, not an addition
✓ Larger to smaller unit always means multiply
✓ A table's pattern comes from that same one rule
✓ The routine works for length, weight, capacity, and time

All eight facts are on your reference chart from earlier.

Coming Up Next: Real-World Problems

You can now convert between units and read or build a conversion table.

Next lesson puts that skill inside multi-step word problems — figuring out,
for example, how much ribbon is left after cutting several mixed-unit lengths
from one spool.