The measurement of something along its greatest dimension.
Length is the measurement of how long something is. In math, we usually measure length as the distance from one end of an object to the other—like the edge of a ruler, the side of a rectangle, or the height of a table.
We measure length using standard units such as:
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Inches, feet, yards (in the U.S. customary system)
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Millimeters, centimeters, meters (in the metric system)
For example:
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The length of a pencil might be 15 centimeters.
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A soccer field might be 100 yards long.
Length is one of the most common measurements in math and real life. We use it when:
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Measuring how tall we are
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Describing the size of an object
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Solving geometry problems involving shapes and perimeter
When Do Students Learn About Length?
Students begin learning about length early on when they explore measurements in everyday life.
Grades K–2 – Introduction to Length
Students start by comparing the length of objects and using tools like rulers to measure.
Grades 3–5 – Using Standard Units and Solving Problems
Students work with both metric and U.S. customary units to solve problems involving length, perimeter, and more.
Grades 6+ – Applying Length in Geometry and Algebra
Students use length in formulas, coordinate geometry, and more advanced math topics.
