An inch is a US customary unit of length equal to one twelfth of a foot, about the width of an adult thumb. Its abbreviation is in. Rulers split each inch into halves, quarters, eighths and sixteenths. One inch is exactly 2.54 centimeters, and 12 inches make 1 foot.
Read the last whole inch the object passes, then count the smaller spaces: the pencil reaches 2 and 6 eighths, which is 2¾ inches.
Formal definition and notation
The inch is a unit of length in the US customary system equal to112 of the international foot. Because the foot is defined as exactly 0.3048 m, 1 in = 0.0254 m = 2.54 cm exactly. Lengths smaller than an inch are usually written as fractions with denominators 2, 4, 8 or 16.
A foot is 12 inches. Use inches for small objects and feet for rooms and heights.
Quick check: 3 questions
Question 1 of 3
How long is 30 inches in feet?
Show answer and explanation
Answer: B.30 ÷ 12 = 2.5 feet (2 feet 6 inches). A divides by 10, C multiplies by 12, and D treats the 6 leftover inches as 0.6 foot.
Question 2 of 3
Which length is longest?
Show answer and explanation
Answer: C. In sixteenths: 14 = 416, 38 = 616, 18 = 216, and 316. The largest is 616 = 38.
Question 3 of 3
How many centimeters are in 10 inches?
Show answer and explanation
Answer: D.10 × 2.54 = 25.4. A divides instead of multiplying, B adds 2.54, and C misplaces the decimal point.
Inch: frequently asked questions
How many centimeters are in an inch?
Exactly 2.54 centimeters. The foot is defined as exactly 0.3048 meter, and an inch is one twelfth of that, which is 0.0254 meter, or 2.54 cm. To change inches to centimeters, multiply by 2.54; to change centimeters to inches, divide by 2.54. For estimates, about 2.5 cm per inch is close enough.
How do you read inches on a ruler?
Find the last whole number the object passes; that is the whole inches. Then count the small spaces past it. On a ruler marked in eighths, each space is 1/8 inch, so 6 spaces past 2 is 2 6/8, which simplifies to 2 3/4 inches. The longer a mark, the simpler its fraction: halves are longer than quarters, quarters longer than eighths.
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