🔢 MathGrade 2Lesson 28
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Measure with Rulers Accurately
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Learning Objectives
- 1Place a ruler correctly with the zero mark at the start of an object
- 2Read the inch or centimeter mark at the other end to find the length
- 3Know common household-object lengths in inches and centimeters
- 4Read both edges of a dual-scale US ruler (inches on top, centimeters on bottom)
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Mini Lesson
A ruler is a measuring tool marked with two scales. In the United States, a standard ruler shows inches (in) along the top edge and centimeters (cm) along the bottom edge. Measuring accurately means following three rules every time.
Two scales on one ruler
- Inches (in) — the US customary unit. A 12-inch ruler is about one foot (1 ft = 12 in).
- Centimeters (cm) — the metric unit. A standard US ruler has 30 cm on the other edge. 1 inch is about 2.5 cm.
- Pick the scale you want, then read along that edge only.
Three rules for accurate measuring
- Rule 1 — Line up the zero: place the 0 mark exactly at one end of the object. Not the edge of the ruler — the zero mark!
- Rule 2 — Keep it straight: the ruler must run in a straight line along the object, not at an angle.
- Rule 3 — Read the end mark: look at the number where the other end of the object reaches. That number is the length — in inches if you read the top edge, or centimeters if you read the bottom edge.
Common objects and their lengths
- A standard pencil: about 6 in (about 15 cm)
- A large eraser: about 2 in (about 5 cm)
- A crayon: about 3.5 in (about 9 cm)
- A glue stick: about 3 in (about 7 cm)
- A small paper clip: about 1 in (about 3 cm)
- A new unsharpened pencil: about 7.5 in (about 19 cm)
Common mistake to avoid
- Do not start measuring from the edge of the ruler if the ruler has a gap before the zero mark. Always find and use the 0.
- Do not mix the two edges in one reading. If you start in inches, finish in inches.
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Ask yourself: "Is my zero mark lined up with the start of the object? Which edge am I reading — inches or centimeters?"
Vocabulary
Ruler
A measuring tool with two scales — inches on one edge and centimeters on the othere.g. I used a ruler to measure my pencil.
Inch (in)
A US customary unit of length. 12 inches = 1 foote.g. My pencil is 6 inches long.
Foot (ft)
A US customary unit of length, equal to 12 inchese.g. A ruler is 1 foot long.
Centimeter (cm)
A metric unit of length. 100 cm = 1 metere.g. My eraser is 5 centimeters long.
Length
How long something is from end to ende.g. I measured the length of the crayon.
Zero mark
The 0 line on a ruler where measuring startse.g. I lined up the zero mark with the end of the pencil.
Measure
To find the size of something using a toole.g. We measure to compare two objects.
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