What this calculator does
This tool combines a measurement given in feet, inches and a fraction of an inch into a single value, then rebuilds it as a tidy feet-inches-fraction reading. It is ideal for carpentry, construction, sewing and any task where a tape measure shows fractional inches.
How to use it
Enter the whole feet, whole inches, and the fraction as a numerator over a denominator (for example 3 over 4 for three-quarters). Pick the precision you want the answer rounded to, from 1/2 down to 1/32 of an inch. The calculator returns the total in decimal inches, the total in decimal feet, and a clean feet-inches-fraction reading.
The formula explained
First everything is converted to inches: $$\text{Total Inches} = 12 \times \text{Feet} + \text{Inches} + \frac{\text{Numerator}}{\text{Denominator}}$$ Total feet is simply that value divided by 12: $$\text{Total Feet} = \dfrac{12 \times \text{Feet} + \text{Inches} + \frac{\text{Numerator}}{\text{Denominator}}}{12}$$ To rebuild the reading, the whole feet are taken as the floor of total inches divided by 12, the leftover inches are the floor of the remainder, and the remaining decimal is rounded to the nearest 1/precision and reduced to lowest terms: $$\begin{gathered} \text{Fraction} = \frac{\operatorname{round}(F \cdot P)}{P} \\[1.5em] \text{where}\quad \left\{ \begin{aligned} F &= \text{fractional part of an inch} \\ P &= \text{Precision} \end{aligned} \right. \end{gathered}$$
Worked example
For 5 ft 8 3/4 in: \(5 \times 12 = 60\), plus 8 = 68, plus \(3/4 = 0.75\), giving 68.75 total inches and \(68.75 / 12 = 5.7292\) feet. Rebuilt at 1/16 precision this is 5 ft 8 12/16, which reduces to 5 ft 8 3/4 in.
FAQ
Can I enter an improper fraction? Yes. Something like 9/4 inches is fully valid and will roll over into whole inches automatically.
What does the precision option do? It controls the smallest fraction the answer is rounded to, matching the markings on your tape measure.
Does it reduce fractions? Yes, the fraction is always reduced to lowest terms, so 12/16 becomes 3/4.
