Feet and Inches to Decimal Feet: Formula and Examples
Convert 8 ft 6 in to 8.5 feet, handle fractional inches, and convert decimal feet back to feet and inches without confusing inches with decimals.
Decimal feet = whole feet + (inches ÷ 12). So 8 ft 6 in = 8.5 ft, and 5 ft 7½ in = 5.625 ft. The inches must be divided by 12; writing 8.6 feet for 8 ft 6 in gives the wrong length.
Convert a measurement in three steps
For 5 ft 7½ in:
- Convert the inch fraction to a decimal:
7 + 1 ÷ 2 = 7.5 in. - Divide the inches by 12:
7.5 ÷ 12 = 0.625 ft. - Add the whole feet:
5 + 0.625 = 5.625 ft.
A second route is total inches: 5 × 12 + 7.5 = 67.5 in. Open the US unit converter, choose Length → Inches → Feet, and enter 67.5. The converter accepts one numeric value, so do not paste 5' 7 1/2" into its input.
Quick inch-to-foot reference
Add the value in the second column to the whole-foot part of your measurement. Repeating decimals are rounded here for display only.
| Inches | Decimal feet |
|---|---|
| 1/4 in | 0.020833… ft |
| 1/2 in | 0.041666… ft |
| 1 in | 0.083333… ft |
| 2 in | 0.166666… ft |
| 3 in | 0.25 ft |
| 4 in | 0.333333… ft |
| 6 in | 0.5 ft |
| 8 in | 0.666666… ft |
| 9 in | 0.75 ft |
| 10 in | 0.833333… ft |
| 11 in | 0.916666… ft |
Use the result in an area calculation
A room 14 ft 6 in × 11 ft 3 in becomes 14.5 × 11.25 = 163.125 sq ft. Convert both measurements before multiplying; converting only one mixes units.
Keep the full result while adding rooms or applying material coverage. The square-footage guide shows how to handle L-shaped spaces and ordering allowances.
For concrete, depth must use the same unit as the other dimensions. The cubic-yard guide shows a slab with a depth specified in inches.
Convert decimal feet back to feet and inches
Take the whole number as feet. Multiply the remainder by 12.
For 9.375 ft: 0.375 × 12 = 4.5 in, giving 9 ft 4½ in.
If a drawing requires a particular fraction, round the inches to that fraction at the end. For example, 5.625 inches = 5⅝ inches exactly; rounding it to a coarser fraction changes the length. Do not invent a tolerance from the calculator display.
Common errors and limits
8.6 ft is 8 ft 7.2 in. Decimal digits are parts of a foot, not inches. That 1.2-inch difference can matter in a cut list.
These examples use positive jobsite lengths. For a signed elevation such as minus 2 ft 6 in, apply the sign to the whole measurement: −(2 + 6 ÷ 12) = −2.5 ft.
NIST's general tables of units give the 12-inch foot. Ordinary building measurements use the international foot; legacy survey coordinates require their stated datum and unit definition. See the construction conversion chart for metric equivalents and unit limits.
Use the related US tools
Check the next part of your estimate
How to Calculate Square Footage: Rooms, Walls and Cutouts
Calculate square feet from feet and inches, work through an L-shaped room, subtract openings, and turn measured area into a material order.
How to Calculate Concrete in Cubic Yards
Calculate slab concrete from feet and inches, convert cubic feet to yards, and check a 20-by-12-foot example with the allowance shown separately.
US Construction Unit Conversion Chart
A practical construction conversion reference for inches, feet, square feet, cubic yards, US gallons, pounds, PSI and common metric units.