When a measurement is written as 1 ft 8 in, it means one foot plus eight inches. Convert the inches to a fraction of a foot by dividing by 12, then add the whole feet:
Decimal feet = feet + (inches ÷ 12)
| Written measurement | Calculation | Decimal feet | Total inches |
|---|---|---|---|
| 1 ft 8 in | 1 + (8 ÷ 12) | 1.6667 ft | 20 in |
| 2 ft 10 in | 2 + (10 ÷ 12) | 2.8333 ft | 34 in |
| 5 ft 6 in | 5 + (6 ÷ 12) | 5.5 ft | 66 in |
Because 12 inches = 1 foot, the inches part must be less than 12 when written as a normalized feet-and-inches measurement. For example, 2 ft 14 in can be rewritten as 3 ft 2 in.
Read the notation carefully
A phrase such as “1 8 in feet” may mean 1 ft 8 in converted to feet, but it could also mean something else if punctuation or units are missing. If the intended quantity is 1.8 inches, that is 0.15 ft (1.8 ÷ 12), not 1 ft 8 in. Likewise, “2 feet 10” is interpreted here as 2 ft 10 in; confirm that the original source means inches.
To convert decimal feet back to feet and inches, keep the whole-number feet, multiply the decimal remainder by 12, and express the result in inches. For example, 2.8333 ft is about 2 ft plus (0.8333 × 12) ≈ 10 in.
These are length conversions. They do not determine which dimension—height, width, depth, or length—a source is describing. For the unit definitions, see NIST's conversion reference.