Feet to Inches Converter

Article — Feet to Inches Converter

Feet to Inches: Formula, Heights, Lumber, and TV Sizes

To convert feet to inches, multiply by 12. The relation is exact: 1 foot = 12 inches, fixed by definition since the 1959 International Yard and Pound Agreement (1 ft = 0.3048 m exactly, so 1 in = 0.0254 m). Common conversions: 5 ft = 60 in, 6 ft = 72 in, 10 ft = 120 in. Decimal feet are not the same as feet-and-inches notation — 5.5 ft means 5 ft 6 in, not 5 ft 5 in.

Feet and inches are the standard units of length in the US customary system, and they remain common in the UK, Canada, and aviation worldwide for height, lumber, ceiling clearance, screen diagonals, and altitude. The 12:1 ratio is not a quirk — it traces back to ancient Rome and has practical advantages over a decimal split.

The exact relation: 1 foot = 12 inches

Multiplying feet by 12 gives inches. There is no rounding, no measurement uncertainty, no "approximately". The relation has been exact by definition since the United States, the United Kingdom, Canada, Australia, New Zealand, and South Africa signed the 1959 International Yard and Pound Agreement. The agreement set 1 yard = 0.9144 m exactly, which makes 1 foot = 0.3048 m and 1 inch = 25.4 mm, all exact.

The reverse, inches to feet, divides by 12. Whole-inch values often give non-terminating decimals: 70 in = 5.833… ft, 100 in = 8.333… ft. That is why heights are usually written as feet and inches (5 ft 10 in) rather than decimal feet. The mixed notation avoids the recurring decimals.

Why 12 and not 10

The 12:1 ratio is a Roman legacy. The Roman foot (pes) was about 29.6 cm and was divided into 12 unciae. That word, uncia (one-twelfth), gave English both inch and ounce. Twelve was chosen because it is a highly composite number — it divides evenly into halves (6), thirds (4), quarters (3), and sixths (2), all whole inches. Ten only splits cleanly into halves and fifths. A carpenter with a 12-inch ruler can mark thirds and quarters without fractions; a 10 cm ruler gives 3.33 cm thirds.

Reading and writing human height

In the United States and United Kingdom, adult height is normally given in feet and inches, written with a prime and double-prime: 5′10″ (5 feet 10 inches). To convert to total inches, multiply the feet by 12 and add the inches: (5 × 12) + 10 = 70 in. To convert to centimetres, multiply the total inches by 2.54: 70 × 2.54 = 177.8 cm.

CDC NHANES data (2015–2018) puts the average US adult male at 175.4 cm (5′9″) and female at 161.7 cm (5′3.6″). The 50th percentile range for men is 5′8″ to 5′10″ (172.7 to 177.8 cm). NBA average height is around 6′6″ (198 cm), and the tallest verified person, Robert Wadlow, reached 8′11.1″ (272 cm) before his death in 1940.

Construction, lumber, and ceiling heights

North American lumber comes in fixed lengths measured in feet: 8, 10, 12, 14, and 16 ft are the standard 2x4 stock (nominally 2 by 4 inches, actually 1.5 by 3.5 inches after milling). A standard sheet of plywood is 4 ft × 8 ft = 48 in × 96 in. Residential ceilings are typically 8 ft (96 in), with newer construction at 9 ft or 10 ft. The shipping industry uses the foot too: a standard intermodal container is 20 ft (240 in / 6.10 m) or 40 ft (480 in / 12.19 m). Container ship capacity is measured in TEU (twenty-foot equivalent units).

TV diagonals and screen sizes

TV and monitor sizes are stated as a single number in inches, measuring the screen diagonal. A 55-inch TV has a 55-inch diagonal, equal to 55/12 = 4.58 ft (4 ft 7 in). For a 16:9 widescreen, the width is 87.16 percent of the diagonal and the height is 49.03 percent. So a 55-inch screen is 47.94 in wide and 26.97 in tall — roughly 48 × 27 in. A 65-inch widescreen is about 57 in wide (4 ft 9 in), useful when measuring the wall before purchase.

Fractional feet on tape measures

Imperial tape measures mark inches and binary fractions of an inch: 1/2, 1/4, 1/8, 1/16, sometimes 1/32. They do not mark decimal fractions. When a plan specifies a length as 5 1/2 ft, multiply the whole part by 12 (5 × 12 = 60) and add the inches the fraction represents (1/2 ft = 6 in), giving 66 in. For 5 3/4 ft: 60 + 9 = 69 in.

Common fractional feet on construction plans: 1/8 ft = 1.5 in, 1/4 ft = 3 in, 1/3 ft = 4 in, 1/2 ft = 6 in, 2/3 ft = 8 in, 3/4 ft = 9 in, 5/6 ft = 10 in. The thirds and sixths come out as whole inches because 12 is divisible by 3 and 6.

The 64-year story of the US Survey Foot

From 1959 to 2022, the United States officially used two definitions of the foot at once. The International Foot was 0.3048 m exactly. The US Survey Foot was 1200/3937 m, about 0.30480061 m. The 2 parts-per-million gap accumulated to tens of metres of error over the area of a US state. NIST and NOAA jointly retired the Survey Foot on 1 January 2023, 64 years after the "temporary" agreement that introduced it. Engineering plans, geodetic surveys, and state plane coordinate systems now use the International Foot only.

Common conversion mistakes

The most common error is treating feet-and-inches notation as a decimal. 5′10″ is 70 inches; 5.10 ft is 61.2 inches. They differ by 8.8 inches. Spreadsheets and quick-typed forms often mishandle this, so always convert to a single unit (total inches or pure decimal feet) before doing arithmetic.

The second is forgetting that decimal feet rounds the inches awkwardly. A height entered as 5.5 ft equals 5 ft 6 in exactly (the 0.5 of a foot is 6 inches), but 5.6 ft is 5 ft 7.2 in, not 5 ft 6 in. The third mistake is assuming the inch is exactly 2.5 cm. The exact value is 2.54 cm — the 1.6 percent gap matters for any precise work.

• 1 ft = 12 in (exact by definition)
• 1 ft = 0.3048 m (exact since 1959)
• 1 in = 2.54 cm (exact since 1959)
• 5 ft = 60 in = 152.4 cm
• 5′10″ = 70 in = 177.8 cm (US male average)
• 6 ft = 72 in = 182.88 cm
• 8 ft = 96 in, plywood sheet length
• 20 ft = 240 in, shipping container length
• 35,000 ft = 10,668 m, cruise altitude
• 1/2 ft = 6 in, 1/4 ft = 3 in, 1/3 ft = 4 in