Estimating basics
Feet and Inches to Decimal Calculator
Drawings give sizes as feet, inches and a fraction, but spreadsheets and takeoff tools want a single decimal number. Enter the three parts and get total inches, decimal feet and millimeters. The math is exact, so 1/16 in and every fraction above it convert without rounding error.
Result
Planning estimate- Total inches
- 36.5000 in
- Decimal feet
- 3.04167 ft
- Millimeters
- 927.10 mm
- Normalized size
- 3' 0 1/2"
How it is calculated
- 1 Total inches = feet x 12 + inches + fraction, where the fraction is a whole number of sixteenths divided by 16.
- 2 Decimal feet = total inches / 12.
- 3 Millimeters = total inches x 25.4. One inch is exactly 25.4 mm.
- 4 The normalized size rewrites the total as feet, whole inches and a reduced fraction, so 14 in + 1/2 in shows as 1' 2 1/2".
- 5 Calculations use exact fractions rather than floating point, so the results carry no drift.
Assumptions to confirm
- Fraction precision
- The fraction list stops at sixteenths. If a dimension is finer than that, enter the decimal inches in the inches box and the normalized size will be rounded to the nearest 1/16 in.
- Inch definition
- Uses the international inch (25.4 mm) and foot (0.3048 m). Survey feet differ by about 2 parts per million, which is far below anything that matters for doors, frames or finishes.
- Example size
- The pre-filled 3' 0 1/2" is only an example so the results show on first load. Replace it with your own dimension.
- Rounding in the display
- Results are shown to 4 to 5 decimal places. Round to the precision your schedule or supplier works to.
This is an early planning estimate, not a quotation. Check quantities against your drawings, your specification and the manufacturer's data.
Questions about this calculator
How do I convert 3'-0 1/2" to decimal feet?
Total inches are 3 x 12 + 0 + 1/2 = 36.5. Divide by 12 to get 3.04167 ft.
What is 1/16 of an inch as a decimal?
1/16 in is 0.0625 in, or 1.5875 mm. Each step up the fraction list adds another 0.0625 in.
Why do estimators use decimal feet?
Quantities, areas and unit costs multiply cleanly in decimals, and most spreadsheets cannot read 3'-0 1/2" as a number. Convert once, then calculate.
What if my inches are more than 11?
Enter them anyway. 42 in with 0 feet gives 3.5 ft, and the normalized size shows it as 3' 6".
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- Waste Factor Add a waste allowance to a net quantity and round up to whole packs. Open
Take these numbers off the drawings
Estimateria reads the door, hardware and finish schedules out of your PDFs into a priced grid, so the quantities you check here start from the set instead of a retype.