Feet and Inches Calculator
Add, subtract, multiply, or divide two measurements while keeping feet, inches, fractional inches, decimal values, and area results consistent.
Measurements
Live result
Calculation details
| Item | Feet and inches | Decimal feet | Total inches |
|---|---|---|---|
| First measurement | 5 ft 7 1/2 in | 5.625000 | 67.500000 |
| Second measurement | 2 ft 4 3/4 in | 2.395833 | 28.750000 |
| Result | 8 ft 0 1/4 in | 8.020833 | 96.250000 |
How to use the feet and inches calculator
What this calculator does
This calculator performs arithmetic with two measurements written in feet and inches. It converts each measurement to a single canonical value in inches, applies the selected operation, and then formats the result in the most useful units. Addition and subtraction return a length. Multiplication returns an area in square feet and square inches. Division returns a unitless ratio because identical length units cancel. The tool is intended for measurement arithmetic and estimation; it does not account for construction tolerances, material waste, cutting allowances, or code requirements.
When to use it
Use it to combine room dimensions, subtract an opening from a board length, multiply a length by a width to estimate area, or compare two dimensions as a ratio. It is especially helpful when measurements include fractional inches and would otherwise require repeated conversions between twelfths of a foot and common inch fractions.
How to calculate
- The calculator opens with a complete demonstration: 5 ft 7 1/2 in plus 2 ft 4 3/4 in. The result and a validated example workbook are available immediately.
- Replace the first and second measurements. Each feet or inches box accepts an integer, a decimal using a period, a fraction such as 3/8, or simple arithmetic such as 2+1/4. Scientific notation and decimal commas are intentionally rejected.
- Choose Add, Subtract, Multiply, or Divide. The result panel, detail table, summary pills, and workbook model update live.
- Choose the Fraction precision used to display fractional inches. The calculation retains full precision; only the mixed-fraction presentation is rounded.
- Select Download Excel to save the current inputs and results as a real .xlsx workbook. Reset clears the demonstration and all data, so export becomes unavailable until a complete valid state is entered again.
Input guide
First measurement – feet and Second measurement – feet are required length components. Enter a finite arithmetic expression, normally zero or greater, such as 5 or 2.5. A negative component is allowed when you intentionally need a signed measurement, but mixing negative feet with positive inches can be easy to misread; the calculator treats the two components algebraically. Increasing either operand changes the result according to the selected operation.
First measurement – inches and Second measurement – inches are also required. Enter values such as 7.5, 7+1/2, or 15/2. Inches may exceed 12 because the calculator normalizes the final length automatically. A frequent mistake is typing a decimal comma such as 7,5; use 7.5 instead. Another is dividing by a second measurement that equals zero, which is rejected.
Operation determines the dimensional meaning of the answer. Add and Subtract operate on total inches and return length. Multiply treats the measurements as two sides and returns area. Divide returns the first total length divided by the second. Fraction precision selects denominators from 2 through 64. A finer denominator can display more detail but does not make an imprecise physical measurement more accurate.
Output guide
Live result is the principal formatted answer. For length operations, it is shown as normalized feet, whole inches, and a reduced fractional inch. Decimal feet expresses the same length as feet with decimals; Total inches expresses it entirely in inches; Metric equivalent uses the exact international conversion of 1 inch = 0.0254 meter. The Fractional inches card presents the whole result in inches with the selected common fraction. For multiplication, the cards instead report square feet, square inches, and square meters. For division, they report the ratio and the two source lengths.
The Calculation details table shows both operands and the result from the same canonical model used by the page and workbook. A zero addition result means the signed measurements cancel. A negative subtraction result means the second measurement is longer than the first. A large area is not a material order recommendation; apply project-specific waste and coverage factors separately.
Worked example
The opening example converts 5 ft 7 1/2 in to 67.5 inches and 2 ft 4 3/4 in to 28.75 inches. Addition gives 96.25 inches, which normalizes to 8 ft 0 1/4 in. Decimal feet are 96.25 ÷ 12 = 8.020833 ft, and the metric equivalent is 96.25 × 0.0254 = 2.44475 m. These are the same values used by the live result and exported workbook.
Learn more
The conversion is anchored to the internationally defined inch. NIST explains the relationship between U.S. customary and SI units in its SI unit guidance for length. For broader measurement practice and correct unit symbols, consult the NIST Guide for the Use of the International System of Units.
How the arithmetic works
Total inches = (feet × 12) + inches. Addition or subtraction is performed on total inches. Area in square inches = first total inches × second total inches. Ratio = first total inches ÷ second total inches.
After addition or subtraction, the calculator separates total inches into feet and the remaining inches. Fractional inches are rounded to the chosen denominator and reduced by their greatest common divisor. When rounding produces exactly 12 inches, the display carries that amount into the next foot. This keeps values such as 6 ft 11 31/32 in from displaying an impossible 6 ft 12 in at coarse precision.
Measurement accuracy and practical limits
Displayed precision and real-world accuracy are different. Selecting 1/64 inch changes formatting, but it cannot improve a measurement taken with a tape marked only to 1/16 inch. For construction and fabrication, carry enough precision through the arithmetic, then round only at the point where the tool, material, or specification requires it. The NIST overview of SI units provides context for traceable metric measurements and unit definitions.
For area estimates, confirm that both measurements describe perpendicular sides in compatible conditions. Openings, irregular shapes, kerf, seams, overlaps, and waste are separate considerations. The calculator reports the exact arithmetic implied by the entered values; professional plans may require additional tolerances and standards.