The conversion is based on simple arithmetic:

1. Input Standard Measurement: Enter the number of whole feet and the number of inches. The inches can be a decimal (e.g., 6.5) or a fraction (which you must first convert to a decimal, e.g., 5/8 = 0.625).
2. Calculate Total Inches: The calculator first converts the feet to inches by multiplying by 12, then adds the inch value.
   Total Inches = (Feet × 12) + Inches
3. Calculate Decimal Feet: The total inches are then divided by 12 to get the equivalent measurement in decimal feet.

Example 1: A rough opening of 5′ 6½″.
CAD wants a single decimal. Total inches = (5 × 12) + 6.5 = 66.5″. Decimal feet = 66.5 ÷ 12 ≈ 5.5417 ft. Enter that in the model and the opening matches the tape.

Example 2: Adding two runs on the bench.
A 4′ 7″ top rail plus a 2′ 10″ return: convert both to inches (55 + 34 = 89″), then back: 89 ÷ 12 = 7 remainder 5, so 7′ 5″ of total run. Working in one unit first is what keeps fractions from going wrong.

Example 3: Reading a decimal back to the tape.
A spreadsheet hands you 3.75 ft. That's 3 ft plus 0.75 × 12 = 9 inches, so mark 3′ 9″ — not "3 feet 75 inches."

"The dangerous number in this trade is a decimal inch. To a machinist 2.375 is exact, but a field carpenter may hear '2 point 3' and mark 3/10 inch, which is nearly a quarter-inch off. Always say the unit out loud — 'two and three-eighths inches' — and write it with a symbol." — Finish Carpenter

"When a drawing mixes formats, I convert everything to decimal inches once at the top of the cut list, do all the math there, and only translate back to feet-and-fractions when it's time to mark the wood. One conversion, done carefully, beats ten done in your head."

• Entering numbers in CAD or a CNC program that only accept a single decimal value, not a stacked feet-and-fraction notation.
• Turning a tape-measure reading into a spreadsheet cell so cut lists, material takeoffs, and cost formulas can do arithmetic on them.
• Checking a framer's or estimator's decimal-feet figure against the fraction you will actually mark on the lumber.
• Adding and subtracting runs of stock by converting each to inches first, summing, then converting the total back to feet and inches.
• Reading architectural dimensions where 12.5 means twelve and a half feet rather than twelve feet five inches.

• Fractional Inches: The standard way measurements are read on an imperial tape measure (e.g., 1/2", 3/8", 15/16").
• Decimal Inches: Inches expressed as a decimal value (e.g., 0.5", 0.375", 0.9375"). This format is easier for calculations.
• Decimal Feet: Feet expressed as a decimal value (e.g., 1.5 ft, 2.75 ft).

• Incorrect Fraction Conversion: A common mistake is incorrectly converting a fraction to a decimal (e.g., confusing 5/8 with 0.58). Always divide the top number by the bottom number (5 ÷ 8 = 0.625).
• Mixing up Tenths and Sixteenths: Confusing a decimal like 0.6 feet with 6 inches. 0.6 feet is actually 7.2 inches (0.6 * 12).