Convert whole and fractional inches into decimal feet with an accurate twelve-inch ruler, a 5 ft 7⅜ in worked example, reverse check and rounding guidance.
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The calculation
Decimal feet = total inches ÷ 12. For feet plus leftover inches: decimal feet = whole feet + (leftover decimal inches ÷ 12). Convert a fractional inch a/b into decimal inches as a ÷ b first.
Worked example
5 ft 7⅜ in = 60 + 7 + 3/8 = 67.375 in. Divide by 12: 67.375/12 = 5.614583… ft, or 5.6146 ft to four decimal places. Equivalently, 5 + 7.375/12 = 5.614583… ft. Multiplying the rounded value by 12 gives 67.3752 in; the 0.0002-in difference comes from rounding.
The decimal part is a portion of a foot. The value 7.375 in is decimal inches, not 7.375 ft. Keep units visible, use the exact 12 in/ft relationship and round at the end to an appropriate precision for the measurement.
Video chapters
- 0:00 — What does decimal feet mean?
- 0:15 — Twelve inches make one foot
- 0:31 — Start with a whole-inch example
- 0:47 — First make the fraction decimal inches
- 1:01 — Combine the entire measurement
- 1:16 — Divide by twelve for decimal feet
- 1:37 — Multiply back to check
- 1:55 — Decimal inches are not decimal feet
- 2:14 — A reusable two-step method
Read the full transcript
How do you turn inches into decimal feet? The digits after the decimal represent a fraction of a foot, not a count of inches. Imagine a board measuring five feet, seven and three eighths inches. We will convert it, then check the answer in inches.
The unit bridge is exact: one foot is twelve inches. A twelve-inch ruler fills one foot-long box. To convert inches into feet, divide by twelve. You are counting the twelve-inch boxes. The units cancel: inches divided by inches per foot leaves feet.
Try thirty inches. Two full rulers account for twenty-four inches; the six-inch remainder is half a ruler. So thirty divided by twelve is two point five feet. Reverse it: two point five feet times twelve inches per foot gives thirty inches.
Now take seven and three eighths inches. The fraction is three divided by eight, or zero point three seven five inch. Add the seven whole inches: seven point three seven five inches. This is decimal inches. It is not yet decimal feet.
Five whole feet contain sixty inches. Add the remaining seven point three seven five inches. The total is sixty-seven point three seven five inches. Convert that total in one step, or keep the five whole feet and convert only the leftover inches.
Using the total route, sixty-seven point three seven five divided by twelve is five point six one four five eight three, with more digits following. Or divide seven point three seven five by twelve to get zero point six one four five eight three feet, then add five feet. Both routes give about five point six one four six feet to four decimal places.
Multiply the rounded answer by twelve. Five point six one four six feet gives sixty-seven point three seven five two inches. The original was sixty-seven point three seven five inches. That tiny difference is rounding. Keeping the exact fraction would return the original length exactly.
Watch the unit. Seven point three seven five inches is short; seven point three seven five feet is twelve times longer. Do not simply put inches digits after a feet decimal point. Divide the inch remainder by twelve. Useful anchors: three inches is a quarter foot, six is half, and nine is three quarters.
The method is simple. Convert a fractional inch to decimal inches: numerator divided by denominator. Combine the inches and divide by twelve. Or add whole feet after dividing only the leftover inches. Keep units visible, then round to the precision you need. Five feet, seven and three eighths inches is about five point six one four six feet.
Sources
- NIST — customary length conversion factors
- NIST — exact inch definition
- NIST — international foot definition
- OpenStax — converting a fraction to a decimal