How to Convert Feet to Inches
Converting feet to inches is a straightforward yet frequently needed conversion within the imperial measurement system. Both feet (ft) and inches (in) are imperial units of length, with one foot equaling exactly 12 inches. This is one of the most basic unit conversions taught in schools and used in everyday life across the United States, United Kingdom, and other countries that use imperial measurements. The conversion is essential for expressing height in inches for medical records, calculating material lengths in construction and carpentry, and working with dimensions in crafts, sewing, and interior design. Builders and contractors regularly convert between feet and inches when measuring lumber, piping, and other materials. When someone says they are 5 foot 10, understanding that this equals 70 inches is useful for comparing standardized measurements. Fashion and retail industries use inches for waist, inseam, and other garment measurements that may initially be taken in feet and inches. Our converter handles this simple but important calculation instantly, making it easy to work with both expressions of imperial length.
Conversion Formula
To convert feet to inches, multiply the number of feet by 12, since there are exactly 12 inches in every foot. This is an exact relationship within the imperial system. For mixed measurements (like 5 feet 6 inches), multiply the feet by 12 and add the remaining inches: (5 × 12) + 6 = 66 inches.
Inches = Feet × 12
5.5 feet = 66 inches
Step-by-Step Example
To convert 5.5 feet to inches:
1. Start with the value: 5.5 feet
2. Multiply by the conversion factor: 5.5 × 12
3. Calculate: 5.5 × 12 = 66
4. Result: 5.5 feet = 66 inches
This is equivalent to 5 feet 6 inches, a common height for adults.
Understanding Feet and Inches
What is a Foot?
The foot has ancient origins, historically based on the length of a human foot. Different civilizations had varying definitions, from the Roman "pes" (about 11.65 inches) to the Greek "pous." The modern international foot was standardized in 1959 through an international agreement between six English-speaking nations, defining it as exactly 0.3048 meters (or 12 inches of 25.4 mm each). The foot remains a primary unit of measurement in the United States and is still commonly used in the United Kingdom, Canada, and other nations for everyday height and distance measurements.
What is a Inch?
The inch has been used for centuries, with its name derived from the Latin "uncia" meaning one-twelfth, referring to its relationship as one-twelfth of a foot. Historically, it was defined as the width of a man's thumb, or three barleycorns placed end to end. King Edward II of England decreed in the 14th century that an inch equaled three barleycorns. The modern international inch was standardized in 1959 as exactly 25.4 millimeters. Despite metrication efforts, the inch remains widely used in the US, UK, and Canada for everyday measurements, screen sizes, and technical specifications.
Practical Applications
Feet to inches conversion is used daily in construction for precise lumber and material measurements. Medical records often require height in total inches for BMI calculations and growth charts. Real estate listings may give ceiling heights in feet that need converting to inches for crown molding or fixture installation. Sewing and crafting projects often use inch measurements for patterns that describe fabric lengths in feet. Sports equipment sizing, such as ski length or surfboard dimensions, may require this conversion. TV and monitor screen sizes are measured diagonally in inches, while room dimensions are typically in feet.
Tips and Common Mistakes
Since this is an exact conversion (1 foot = 12 inches), there is no rounding error to worry about. The main mistake people make is with mixed measurements. When someone says "5 foot 10," this is 5 feet plus 10 inches, not 5.10 feet. To convert to total inches: (5 × 12) + 10 = 70 inches, not 5.10 × 12 = 61.2 inches. This distinction between decimal feet and feet-and-inches notation is critical. Another common error is confusing linear feet with board feet in lumber calculations, as board feet include width and thickness dimensions.
Frequently Asked Questions
There are exactly 12 inches in one foot. This is a precise, defined relationship within the imperial system, not an approximation. The foot has been subdivided into 12 inches since at least the Roman era, where the "pes" was divided into 12 "unciae." The number 12 was historically preferred because it is divisible by 2, 3, 4, and 6, making fractions easier to work with.