Feet and Inches Calculator
Enter two measurements in feet, inches, and fractional inches, then choose an operation to add or subtract them. Results are shown in feet-inches-fractions, decimal feet, and total inches.
Estimate only — not professional advice. Always verify results independently before purchasing materials or beginning work. Terms of Use
What is Feet and Inches?
A feet and inches calculator performs arithmetic on imperial measurements that include feet, whole inches, and fractional inches down to sixteenths. Working with these mixed units by hand is tedious and error-prone because you must manage carries between fractions, inches, and feet. This calculator handles the conversions automatically and displays the result in multiple useful formats. Imperial measurements remain standard in US construction, woodworking, and building trades. Lumber dimensions, room measurements, tape measure readings, and architectural plans all use feet, inches, and fractions. Common fractional increments on a standard tape measure are 1/16, 1/8, 1/4, and 1/2 inch. Adding two measurements like 5 feet 7 inches and 3 feet 9 inches requires carrying 16 inches into 1 foot and 4 inches, yielding 9 feet 4 inches. While straightforward for simple values, fractions make this arithmetic significantly harder. The calculator supports two operations. Addition combines two measurements, which is useful for finding total lengths when joining boards, summing wall segments, or calculating perimeters. Subtraction finds the difference between two measurements, commonly needed when cutting material to fit a space or calculating remaining stock after a cut. All results are displayed in three formats. The feet-inches-fraction format matches how measurements appear on tape measures and plans. Decimal feet is useful for calculations, spreadsheets, and converting to metric. Total inches simplifies comparison and further arithmetic. The fraction output is reduced to the simplest form using sixteenths as the base unit, which matches the finest common graduation on standard measuring tapes. This tool is especially valuable on job sites where quick mental math with fractions can lead to costly cutting errors. A single wrong measurement can waste an expensive piece of lumber, trim, or countertop material.
How to Calculate
- Enter the first measurement as feet, inches (0-11), and a fractional inch (0, 1/16, 1/8, 1/4, or 1/2)
- Select the operation: Add or Subtract
- Enter the second measurement
- Read the result in feet, inches, and fraction format
- Use the decimal feet or total inches output if you need the value in a single unit
- For subtraction, negative results are clamped to zero
Formula
Total Inches (Value) = Feet x 12 + Inches + (Fraction Sixteenths / 16) Add: Result = Value1 + Value2 Subtract: Result = max(0, Value1 - Value2) Converting back: Result Feet = floor(Total Result Inches / 12) Remaining Inches = Total Result Inches - (Result Feet x 12) Result Whole Inches = floor(Remaining Inches) Result Fraction = round((Remaining - Whole) x 16) sixteenths, reduced to simplest form Decimal Feet = Total Result Inches / 12
Example Calculation
Adding 5 ft 7 in and 3 ft 9 in (no fractions, default values): Value 1 = 5 x 12 + 7 + 0/16 = 67 inches Value 2 = 3 x 12 + 9 + 0/16 = 45 inches Result = 67 + 45 = 112 inches Feet = floor(112 / 12) = 9 ft Remaining = 112 - 108 = 4 in Fraction = 0 Result: 9 ft 4 in 0 Decimal Feet: 9.3333 ft Total Inches: 112
Frequently Asked Questions
Why does subtraction never go below zero?
The calculator clamps subtraction results to zero because negative lengths are not meaningful in construction measurements. If you need to find which value is larger, swap the inputs so the larger measurement is Value 1.
What fractions are supported?
The input supports 0, 1/16, 1/8, 1/4, and 1/2 inch — the five most common tape measure marks. The output can display any fraction in sixteenths (1/16 through 15/16), automatically reduced to the simplest form like 1/4 or 3/8.
How do I add multiple measurements together?
Add the first two values, note the result in decimal feet or total inches, then use that as Value 1 for the next addition. For quick sums of many measurements, the total inches output is easiest to work with — just add them up and convert at the end.
Can I use this for metric conversions?
This calculator works entirely in imperial units. To convert the decimal feet result to meters, multiply by 0.3048. To convert total inches to centimeters, multiply by 2.54.
Why does my fraction show as 0 when I expect a different value?
Fractions are rounded to the nearest sixteenth of an inch. If your result falls exactly on a whole inch, the fraction displays as 0. Very small remainders below 1/32 of an inch are also rounded to 0.