English Units of Length
English units of length — inches, feet, yards, and miles — are the standard measurements used in Grade 8 math (Yoshiwara Core Math, Chapter 3: Measurement). One foot equals 12 inches, one yard equals 3 feet, and one mile equals 5,280 feet. To convert between units, use a conversion factor (a unit fraction equal to 1) that cancels unwanted units. For example, converting 30 feet to yards means multiplying by (1 yard / 3 feet) to get 10 yards. Mastering these conversions is essential for real-world measurement problems in geometry and applied math.
Key Concepts
Property Units of length: $$1 \text{ foot} = 12 \text{ inches}$$ $$1 \text{ yard} = 3 \text{ feet}$$ $$1 \text{ mile} = 5280 \text{ feet}$$ A conversion factor is a fraction equal to 1, such as $\frac{3 \text{ feet}}{1 \text{ yard}}$. We choose the factor that cancels the old units and leaves the new ones. Such conversion factors are also called unit fractions.
Examples A person is 5 feet 4 inches tall. To express this in inches, calculate $5 \times 12 + 4 = 64$ inches.
A piece of fabric is 90 inches long. To find its length in feet, you divide: $\frac{90}{12} = 7.5$ feet.
Common Questions
How many inches are in a foot?
There are 12 inches in 1 foot. To convert feet to inches, multiply the number of feet by 12.
How many feet are in a mile?
There are 5,280 feet in 1 mile. This is a key conversion fact in the English system.
What is a conversion factor in measurement?
A conversion factor is a fraction equal to 1 that lets you switch between units. For example, (3 feet / 1 yard) = 1, so multiplying by it converts yards to feet.
How do you convert 90 inches to feet?
Divide 90 by 12 (since 1 foot = 12 inches) to get 7.5 feet.
How do you convert 30 feet to yards?
Multiply 30 feet × (1 yard / 3 feet) = 10 yards. The feet units cancel, leaving yards.
How do you express 5 feet 4 inches in total inches?
Multiply the feet by 12 and add the extra inches: 5 × 12 + 4 = 64 inches.