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12 inches per foot — instant total inches
The foot-to-inch conversion is one of the simplest in the imperial system: 1 ft = 12 in exactly. Enter a value in feet — whole number or feet-and-inches notation like 5′10 — and the calculator returns the total in inches straight away.
The formula
in = ft × 12
- ft — the length in feet (can include a fractional part or apostrophe notation).
- in — the equivalent total length in inches.
- 12 — the fixed ratio: 1 foot = 12 inches.
For mixed input (e.g. 5′10): total inches = (5 × 12) + 10 = 70.
Worked example
Using the default of 5′10:
- Feet component: 5 × 12 = 60 inches.
- Add remaining inches: 60 + 10 = 70 inches.
So 5′10″ = 70 inches.
Conversion table — common measurements
| Feet | Inches |
|---|---|
| 1 | 12 |
| 2 | 24 |
| 3 | 36 |
| 4 | 48 |
| 5 | 60 |
| 5′6 | 66 |
| 5′10 | 70 |
| 6 | 72 |
| 6′6 | 78 |
| 7 | 84 |
| 8 | 96 |
| 10 | 120 |
History & standards
The foot has been a unit of measurement since at least ancient Egypt and Rome. In England, the yard was defined as 3 feet, and the foot was divided into 12 inches — a base-12 (duodecimal) system that allows exact thirds and quarters without fractions. The 1959 International Yard and Pound Agreement fixed 1 foot = 0.3048 m exactly, tying the imperial system firmly to the metric. NIST deprecated the slightly different US survey foot in 2023; the international foot is now the sole legal US definition.
Common applications
- Human height. Many US forms ask for height in feet and inches; the equivalent total-inches value is used in BMI and reach calculations.
- Construction & carpentry. Lumber lengths, stud spacings and ceiling heights are often specified in feet with the total-inch equivalent used for cutting.
- Fabric & sewing. Pattern pieces are sometimes given in feet; yardage calculations need the inch equivalent.
- Sports. Running events shorter than a mile are often measured in feet or yards; athletics rules specify dimensions in inches.
- Real estate. Lot and room dimensions are listed in feet; installers often need the total-inches figure for materials.
Reverse conversion
To convert inches back to feet, divide by 12: ft = in ÷ 12. Use the inches to feet calculator for instant results.
Limitations & gotchas
- Decimal feet vs. feet-and-inches. 5.5 ft (decimal) = 5′6″, not 5′5″. The calculator accepts both forms — use the apostrophe to indicate feet-and-inches.
- US survey foot (deprecated 2023). The difference vs. the international foot is about 0.3 mm per mile — negligible for everyday use but relevant for geodetic surveying.
- Rounding. Results are exact for whole-foot inputs. Decimal-foot inputs are converted exactly then rounded to the chosen display precision.
Sources & references
- NIST SP 811, Guide for the Use of the International System of Units (SI).
- BIPM, The International System of Units (SI), 9th edition.
- 1959 International Yard and Pound Agreement.
- Federal Register Vol. 88, No. 60 (2023) — deprecation of the US survey foot.
FAQs
There are exactly 12 inches in one foot. This ratio has been standard since medieval England and was formally fixed by the 1959 International Yard and Pound Agreement alongside the metric definitions.
Multiply the number of feet by 12: inches = feet × 12. For a mixed value like 5′10″, first convert: (5 × 12) + 10 = 70 inches total.
(5 × 12) + 10 = 60 + 10 = 70 inches.
6 × 12 = 72 inches.
Yes. Enter 5′10 in the input field. The calculator reads the apostrophe as the feet/inches separator and returns the total in inches.
The foot predates decimal systems. Its subdivisions (12 inches, 3 feet = 1 yard) allowed easy fractions: halves, thirds, quarters, sixths — useful for trade before calculators. The metric system replaced this with powers of ten, but the foot-inch system persists in the US and informally in the UK.