What is this skill?
Unit conversion means writing a measurement in a different unit. Fourth graders convert from a larger unit to a smaller one, such as 4 feet to inches, 3 minutes to seconds, or 6 meters to centimeters. Because the new unit is smaller, there are more of them, so the number gets bigger.
The tool is multiplication by the conversion factor. Since 1 foot is 12 inches, 4 feet is 4 × 12 = 48 inches. Children learn the common pairs: feet and inches, yards and feet, meters and centimeters, kilometers and meters, pounds and ounces, hours and minutes, minutes and seconds, liters and milliliters, kilograms and grams, gallons and quarts, quarts and pints, days and hours. They also build conversion tables, writing the first few lines (1, 2, 3 …) and spotting the pattern.
Why it matters
Conversions connect measurement with multiplication, and show that the same quantity can be described in different ways. They come up in cooking, travel, sports and any time a child reads a label or a schedule. In science and later math classes, being comfortable with units is a daily need.
The metric system is a good place to see place value in action, since each step is a factor of 10, 100 or 1,000. The customary system (feet, pounds, gallons) has less pattern and asks for more memory, which is why short, regular practice helps. Knowing the size of each unit, such as a yard being about one big step, also lets a child judge whether an answer is sensible.
Common mistakes
- Multiplying when they should divide, or the reverse. In this grade the conversions go from big to small, so the number grows.
- Mixing up the conversion factors, such as saying 1 foot is 10 inches or 1 yard is 12 feet.
- Forgetting the unit in the answer, so “48” stands without “inches.”
- Confusing similar units like quarts and pints, or liters and milliliters.
- Assuming time follows a base-10 pattern. There are 60 seconds in a minute, not 100.
How to help at home
- Measure things in two units. A table might be 3 feet and 36 inches, and a child can see why both are right.
- Make a mini poster of the factors your child needs and keep it on the fridge for a week.
- Cook together and convert: how many pints are in 3 quarts? How many quarts in a gallon?
- Compare units before calculating: “Will there be more inches or feet?” gets children to predict the direction.
- Use a table with a starting row, such as 1 yard is 3 feet, 2 yards is 6 feet, and keep going.
Worked examples
These are real questions from the Tutorsaurus converting units of measurement practice, with the answers worked out.
Example 1
4 feet = ? inches
Answer: 48 inches. 1 foot = 12 inches. 4 × 12 = 48 inches.
Example 2
3 minutes = ? seconds
Answer: 180 seconds. 1 minute = 60 seconds. 3 × 60 = 180 seconds.
Example 3
6 yards = ? feet
Answer: 18 feet. 1 yard = 3 feet. 6 × 3 = 18 feet.