Measuring length by lining up same-size objects
In 1st grade, children learn to measure length by laying same-size objects end to end without gaps or overlaps and counting them.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
Try these with your child
These are real questions from our 1st 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
If a pen is 3 paper clips long, how many paper clips long are two pens?
- 3
- 5
- 6
Why this matters
Once your child understands that a length is a count of equal units, with no gaps or overlaps, a ruler stops being a mystery. In 2nd grade they will use inches and centimeters and notice that smaller units give bigger numbers, and in 3rd grade the same idea leads to area, covering a shape with equal squares. Without it, children often line a ruler up at 1 instead of 0.
Where kids can get stuck
- Leaving gaps between the paper clips or blocks, so the object seems longer than it really is.
- Mixing units of different sizes, like big and small paper clips, and still counting each one as one unit.
- Starting away from the edge of the object, or letting the last unit hang far past the end, and counting it anyway.
How you can help
- Measure a few things at home with same-size objects, such as how many crayons long the table is or how many shoes long the hallway is, laying them end to end.
- Make a deliberate mistake and ask your child to catch it: leave a gap between blocks while measuring and ask whether your measurement is right and why.
- Measure the same item with two different objects, like spoons and forks, and talk about why the numbers are different, without expecting a full explanation yet.
If it’s helpful, you can watch the kid-friendly video below, or sign up for free, adaptive practice in Bobby's Math Club.
Kid-friendly explanation
Questions parents ask
Why is my child measuring with paper clips instead of a ruler?
Measuring with paper clips shows your child what a measurement really is: a count of equal units placed end to end. A ruler does the same thing with the units marked on it. Understanding this first helps children read a ruler correctly later and spot errors, like starting at the wrong place.
Why does it matter that there are no gaps or overlaps?
A gap leaves part of the object uncounted, and an overlap counts part of it twice. Either way, the number no longer matches the real length. Learning to place units carefully, touching but not overlapping, is the same skill needed to read a ruler from zero.
Will my child learn inches and centimeters in 1st grade?
Not usually. In 1st grade, measurement uses everyday objects as units, such as cubes or paper clips. Standard units like inches, feet, centimeters, and meters are introduced in 2nd grade, when children use rulers and other measuring tools and estimate lengths.
Make learning math fun
Bobby's Math Club turns 1st grade math practice into something fun to do together.
- Unlimited free practice
- Questions matched to your child’s level, a few minutes a day
- Hints when they are stuck, and a celebration when it clicks
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 1.MD.A.2: “Express the length of an object as a whole number of length units, by laying multiple copies of a shorter object (the length unit) end to end; understand that the length measurement of an object is the number of same-size length units that span it with no gaps or overlaps. Limit to contexts where the object being measured is spanned by a whole number of length units with no gaps or overlaps.” Learn how Bobby's Math Club can help your students grow. (Common Core 1.MD.2)