Measuring how much longer one thing is
In 2nd grade, children learn to measure two objects and to find how much longer one is than the other, in a standard unit like inches or centimeters.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
Try these with your child
These are real questions from our 2nd grade practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
John jumped 3 feet. Mia jumped 5 feet. How much shorter was John's jump?
- 2 feet
- 8 feet
- 1 foot
Why this matters
Comparing lengths lets your child answer real questions with numbers they measured themselves, turning measuring into a subtraction problem. It also builds careful habits, like measuring both objects from zero with the same unit. Comparing measurements comes up again in 3rd and 4th grade, including lengths with fractions of an inch, and in everyday questions like how much your child has grown since last year.
Where kids can get stuck
- Adding the lengths instead of subtracting, answering 12 inches for how much longer a 7-inch pencil is than a 5-inch marker.
- Measuring one object in inches and the other in centimeters, then subtracting as if the units matched.
- Giving the longer object's length, 7 inches, instead of how much longer it is than the shorter one.
How you can help
- Measure two family members' hands, feet, or arm spans with a ruler or tape, then ask your child how many inches longer one is than the other.
- Compare two toy cars, crayons, or spoons side by side on a ruler, and ask your child to find the difference by looking at the gap and by subtracting.
- Track growth by measuring two plants, or a plant at two times, in centimeters, and talk about how many centimeters taller one has grown.
The kid-friendly video below is a nice one to watch together. For more, Bobby's Math Club has free practice at your child’s level.
Kid-friendly explanation
Questions parents ask
Why is my child learning to find how much longer one object is?
Finding the difference between two lengths connects measuring with subtraction. It helps your child see that comparing amounts is a real-life use of math, and it builds on the comparing word problems they already know. Naming the unit in the answer also builds good habits.
What if my child adds the two measurements instead of subtracting?
Line up the two objects next to each other and point to the part of the longer one that sticks out. Ask, "How long is this extra part?" Seeing that the difference is the gap, not the total, helps your child understand why subtraction is the right choice.
Does it matter which unit my child uses?
Both objects must be measured in the same unit. Your child can use inches or centimeters, but not one of each. If a book is 9 inches and a notebook is 23 centimeters, the numbers cannot be compared directly. Measuring both in the same unit makes the difference meaningful.
Make learning math fun
Bobby's Math Club turns 2nd grade math practice into something fun to do together.
- Free, unlimited practice for every child in your family
- Questions matched to your child’s level, a few minutes a day
- You see their progress and what to work on next
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.
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Join the clubNote for teachers: This skill is covered by Common Core math standard 2.MD.A.4: “Measure to determine how much longer one object is than another, expressing the length difference in terms of a standard length unit.” Learn how Bobby's Math Club can help your students grow. (Common Core 2.MD.4)