Add or subtract lengths in inches (decimal or fraction), feet, centimeters, and millimeters. Enter equations just like you would write it on paper, e.g. 4′ 3 7/8″ + 5 cm.

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See the results in inches, feet, centimeters, and millimeters – all results are in imperial and metric.


How to Add or Subtract Feet & Inches

Adding or subtracting lengths in feet and inches might seem complicated, but it’s actually really easy if you follow a few simple steps. It’s even easier to add or subtract length measurements using a calculator like the one above, but follow these easy steps to learn how to do it yourself.

Step One: Convert Feet and Inches to Decimal

The first thing to do when adding, subtraction, or doing other math with inches, feet, and other measurements is to convert all the measurements into a common unit of measure.

Start by converting inch fractions into decimal. Then convert feet, centimeters, and millimeters to inches.

Convert inch fractions to decimal by dividing the bottom half of the fraction by the bottom half on a calculator. If there is a whole number, add it to the decimal value after converting.

You can also use an inch fraction calculator to quickly find the decimal value for an inch fraction.

For example:3/8 = 3 ÷ 8 = .375 inches

Convert feet to inches by multiplying the number of feet by 12, since there are 12 inches in a foot. Using a feet to inches conversion calculator also simplifies this step.

For example:3 feet = 3 × 12 = 36 inches

Try our other length conversion calculators to convert other units to decimal inches.

Step Two: Add or Subtract the Converted Values

With all measurements in an inch decimal form, add or subtract all measurements as you normally would, using a calculator as needed. The final result will be the length in inches; you can convert the result to any other unit at this point.

To express the sum or difference value in feet, simply multiply by 12.

The following charts simplify the process of adding and subtracting fractional inch values together and might be faster than using a calculator.

Inch Fraction Addition Chart

Table showing the sum of common inch fractions. Add a fraction from the top heading and first column; the sum is where they intersect.+ 1/8″+ 1/4″+ 3/8″+ 1/2″+ 5/8″+ 3/4″+ 7/8″+ 1″1/8″1/4″3/8″1/2″5/8″3/4″7/8″1″
1/4″3/8″1/2″5/8″3/4″7/8″1″1 1/8″
3/8″1/2″5/8″3/4″7/8″1″1 1/8″1 1/4″
1/2″5/8″3/4″7/8″1″1 1/8″1 1/4″1 3/8″
5/8″3/4″7/8″1″1 1/8″1 1/4″1 3/8″1 1/2″
3/4″7/8″1″1 1/8″1 1/4″1 3/8″1 1/2″1 5/8″
7/8″1″1 1/8″1 1/4″1 3/8″1 1/2″1 5/8″1 3/4″
1″1 1/8″1 1/4″1 3/8″1 1/2″1 5/8″1 3/4″1 7/8″
1 1/8″1 1/4″1 3/8″1 1/2″1 5/8″1 3/4″1 7/8″2″

Inch Fraction Subtraction Chart

Table showing the difference of common inch fractions. Subtract a fraction from the top heading from the first column; the difference is where they intersect.− 1/8″− 1/4″− 3/8″− 1/2″− 5/8″− 3/4″− 7/8″− 1″1/8″1/4″3/8″1/2″5/8″3/4″7/8″1″

We’ve covered the basics of adding length measurements, and we hope you’re feeling confident using the steps above. Learn more about how to add feet and inches in our in-depth guide.

How to Multiply or Divide Feet & Inches

The steps to multiply or divide feet and inches are similar to the steps for adding and subtracting above.

Step One: Convert Feet and Inches to Decimal

The first step in multiplying or dividing is to convert the length measurements to a decimal value. If the length measurements are in feet and inches, it might be easiest to convert to inches.

Step Two: Multiply or Divide

With the length value converted to a decimal, it’s now possible to multiply or divide just like you would with any decimal number. For example, if your inch value is 1.25 and you need to multiply by 2, simply multiply using 1.25 × 2 = 2.5.

The following charts make multiplying or dividing fractional inch values much easier.

Inch Fraction Multiplication Chart

Table showing the multiplication of common inch fractions. Multiply the fraction in the first column by the top heading’s value; the result is where they intersect.× 2× 3× 4× 5× 6× 7× 81/8″1/4″3/8″1/2″5/8″3/4″7/8″1″
1/2″3/4″1″1 1/4″1 1/2″1 3/4″2″
3/4″1 1/8″1 1/2″1 7/8″2 1/4″2 5/8″3″
1″1 1/2″2″2 1/2″3″3 1/2″4″
1 1/4″1 7/8″2 1/2″3 1/8″3 3/4″4 3/8″5″
1 1/2″2 1/4″3″3 3/4″4 1/2″5 1/4″6″
1 3/4″2 5/8″3 1/2″4 3/8″5 1/4″6 1/8″7″

Inch Fraction Division Chart

Table showing the division of common inch fractions. Divide the fraction in the first column by the top heading’s value; the result is where they intersect.

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÷ 2÷ 3÷ 4÷ 5÷ 6÷ 7÷ 81/4″1/2″3/4″1″

Inch Fraction and Decimal Equivalents

Sometimes a chart makes things easier: find common inch fractions and equivalent decimal values using this one.