How to Convert Feet to Inches (and Back)
Feet and inches are the two primary units for measuring height and short distances in the United States. While the relationship is simple — there are exactly 12 inches in a foot — converting between them becomes less obvious when dealing with mixed measurements like 5 feet 9 inches or decimal feet like 5.75 ft. This guide covers all the cases.
The Basic Relationship
1 foot = 12 inches (exact, by definition). 1 inch = 1/12 foot = 0.08333... feet.
To convert feet to inches: multiply by 12. For example, 6 ft × 12 = 72 inches.
To convert inches to feet: divide by 12. For example, 66 inches ÷ 12 = 5.5 feet = 5 feet 6 inches.
Why 12 Inches in a Foot?
The foot was historically based on the length of a human foot — a convenient body-based measurement used across ancient civilizations. The division into 12 inches comes from the Roman uncia (one-twelfth).
12 is a practical divisor: it divides evenly into halves (6), thirds (4), quarters (3), sixths (2), and twelfths (1) — useful for carpentry and trade before decimal arithmetic was common.
The barleycorn system further divided the inch into thirds (3 barleycorns = 1 inch), making 36 barleycorns in a foot. This system persists in US shoe sizing, where one shoe size equals one barleycorn (1/3 inch).
Converting Mixed Feet and Inches
To convert a height like 5 feet 9 inches to total inches: (5 × 12) + 9 = 60 + 9 = 69 inches.
To convert total inches back to feet and inches: 69 ÷ 12 = 5 remainder 9 → 5 feet 9 inches.
To convert decimal feet to feet and inches: 5.75 ft → 0.75 × 12 = 9 inches → 5 feet 9 inches.
To convert feet and inches to decimal feet: 5 ft 9 in → 9 ÷ 12 = 0.75 → 5.75 ft.
Height Reference Table
Common heights in feet/inches and total inches:
- 5'0″ = 60 inches
- 5'3″ = 63 inches
- 5'6″ = 66 inches
- 5'9″ = 69 inches
- 6'0″ = 72 inches
- 6'3″ = 75 inches
- 6'6″ = 78 inches
Construction and Measurement Contexts
In US construction, measurements are typically given in feet and inches (e.g., a ceiling that is 8 ft 0 in high, a doorway that is 6 ft 8 in tall). Blueprints and building codes use feet and inches rather than decimal feet.
Lumber is sold in nominal lengths in feet (8 ft, 10 ft, 12 ft) but actual dimensions use inches (a "2×4" board is actually 1.5 inches × 3.5 inches).
Aviation: runway lengths and altitudes use feet. A typical cruising altitude of 35,000 ft = 420,000 inches. Obstacle clearance heights are given in feet.
Conclusion
1 foot = 12 inches exactly. To convert feet to inches, multiply by 12. For mixed measurements (e.g., 5'9″), convert feet to inches first then add the remaining inches: (5 × 12) + 9 = 69 inches. Use our free length converter for instant results.