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Feet-Inch-Fraction Calculator

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Add or subtract two measurements given in feet, inches, and fractions of an inch.

Feet-Inch-Fraction Calculator

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Measurement 1
Measurement 2
Result
9' 10-13/16"
In decimal inches
118.8125"
Fraction result is rounded to the nearest 1/16 inch, the standard precision for most tape measures.

The method

Convert each measurement to total inches: (feet × 12) + inches + fraction Add or subtract the totals Convert back to feet, whole inches, and the nearest 1/16 fraction
Example

6'8-5/16" + 3'2-1/2": converting both to inches and adding gives 9'10-13/16" (118.8125 total inches).

Step-by-step guide

  1. Enter your first measurement in feet, inches, and a fraction (like 5/16).
  2. Choose add or subtract, then enter your second measurement.
  3. Read the combined result in feet-inch-fraction format and decimal inches.

Why converting to a single unit first avoids errors

Adding feet, inches, and fractions directly - column by column - requires careful borrowing and carrying between three different units at once, which is exactly where manual tape-measure math commonly goes wrong (an inch total over 12 needs to carry into feet, a fraction total over 1 needs to carry into whole inches). Converting everything into a single common unit (total inches, including the fractional part as a decimal) first removes that multi-unit juggling entirely - the addition or subtraction becomes simple, and converting back to feet-inches-fraction at the very end is a single, mechanical last step.

Common mistakes

Forgetting to carry when a fraction sum exceeds 1 (like 3/4 + 1/2 = 5/4, which is 1 and 1/4, carrying into the whole inches) - this is the most common manual math error in trade measurements.
Using different fraction denominators without finding a common one first (like adding 1/3 and 1/4 directly) - this calculator handles that automatically, but manual math requires converting to a shared denominator first.

Frequently asked questions

What fraction denominators does this support?

Any fraction you type (like 3/8, 5/16, 1/32) is accepted as input - the result is rounded to the nearest 1/16 inch, matching standard tape measure precision.

Can I use this for subtracting a larger measurement from a smaller one?

Yes - the result will show as negative, indicating the second measurement is larger than the first.

Can I enter just feet, or just inches, without a fraction?

Yes - leave the fraction field blank (or at 0) if your measurement doesn't include one, and the calculator treats it as a whole number of inches.

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