Feet and Inches Calculator
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.
See the results in inches, feet, centimeters, and millimeters – all results are in imperial and metric.
Inches, Feet, Fraction, Centimeters, and Millimeters Results
Imperial Units
Metric Units
On this page:
Joe is the creator of Inch Calculator and has over 20 years of experience in engineering and construction. He holds several degrees and certifications.
How to Add or Subtract Feet and Inches
Calculating feet and inches might seem complicated, but adding and subtracting measurements is actually really easy if you follow a few simple steps. While it’s easy to add or subtract feet and inches using a measurement calculator like the one above, if you follow a few basic steps, you can do it yourself!
Step One: Convert Feet and Inches to Decimal
The first thing to do when adding, subtracting, or doing other math with inches, feet, and other measurements is to convert all the measurements into a common unit of measure. For example, when reading a tape measure, inches will be in fraction form.
Start by converting inch fractions into decimals. 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 foot to inch conversion calculator also simplifies this step.
For example:
3 feet = 3 × 12 = 36 inches
Try our length converter to convert other units to decimal inches.
Step Two: Add or Subtract the Converted Values
With your feet and inch measurements in an inch decimal form, add or subtract them 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
| + 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 1/8″ |
| 1/4″ | 3/8″ | 1/2″ | 5/8″ | 3/4″ | 7/8″ | 1″ | 1 1/8″ | 1 1/4″ |
| 3/8″ | 1/2″ | 5/8″ | 3/4″ | 7/8″ | 1″ | 1 1/8″ | 1 1/4″ | 1 3/8″ |
| 1/2″ | 5/8″ | 3/4″ | 7/8″ | 1″ | 1 1/8″ | 1 1/4″ | 1 3/8″ | 1 1/2″ |
| 5/8″ | 3/4″ | 7/8″ | 1″ | 1 1/8″ | 1 1/4″ | 1 3/8″ | 1 1/2″ | 1 5/8″ |
| 3/4″ | 7/8″ | 1″ | 1 1/8″ | 1 1/4″ | 1 3/8″ | 1 1/2″ | 1 5/8″ | 1 3/4″ |
| 7/8″ | 1″ | 1 1/8″ | 1 1/4″ | 1 3/8″ | 1 1/2″ | 1 5/8″ | 1 3/4″ | 1 7/8″ |
| 1″ | 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
| − 1/8″ | − 1/4″ | − 3/8″ | − 1/2″ | − 5/8″ | − 3/4″ | − 7/8″ | − 1″ | |
|---|---|---|---|---|---|---|---|---|
| 1/8″ | 0″ | -1/8″ | -1/4″ | -3/8″ | -1/2″ | -5/8″ | -3/4″ | -7/8″ |
| 1/4″ | 1/8″ | 0″ | -1/8″ | -1/4″ | -3/8″ | -1/2″ | -5/8″ | -3/4″ |
| 3/8″ | 1/4″ | 1/8″ | 0″ | -1/8″ | -1/4″ | -3/8″ | -1/2″ | -5/8″ |
| 1/2″ | 3/8″ | 1/4″ | 1/8″ | 0″ | -1/8″ | -1/4″ | -3/8″ | -1/2″ |
| 5/8″ | 1/2″ | 3/8″ | 1/4″ | 1/8″ | 0″ | -1/8″ | -1/4″ | -3/8″ |
| 3/4″ | 5/8″ | 1/2″ | 3/8″ | 1/4″ | 1/8″ | 0″ | -1/8″ | -1/4″ |
| 7/8″ | 3/4″ | 5/8″ | 1/2″ | 3/8″ | 1/4″ | 1/8″ | 0″ | -1/8″ |
| 1″ | 7/8″ | 3/4″ | 5/8″ | 1/2″ | 3/8″ | 1/4″ | 1/8″ | 0″ |
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 with 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
| × 2 | × 3 | × 4 | × 5 | × 6 | × 7 | × 8 | |
|---|---|---|---|---|---|---|---|
| 1/8″ | 1/4″ | 3/8″ | 1/2″ | 5/8″ | 3/4″ | 7/8″ | 1″ |
| 1/4″ | 1/2″ | 3/4″ | 1″ | 1 1/4″ | 1 1/2″ | 1 3/4″ | 2″ |
| 3/8″ | 3/4″ | 1 1/8″ | 1 1/2″ | 1 7/8″ | 2 1/4″ | 2 5/8″ | 3″ |
| 1/2″ | 1″ | 1 1/2″ | 2″ | 2 1/2″ | 3″ | 3 1/2″ | 4″ |
| 5/8″ | 1 1/4″ | 1 7/8″ | 2 1/2″ | 3 1/8″ | 3 3/4″ | 4 3/8″ | 5″ |
| 3/4″ | 1 1/2″ | 2 1/4″ | 3″ | 3 3/4″ | 4 1/2″ | 5 1/4″ | 6″ |
| 7/8″ | 1 3/4″ | 2 5/8″ | 3 1/2″ | 4 3/8″ | 5 1/4″ | 6 1/8″ | 7″ |
| 1″ | 2″ | 3″ | 4″ | 5″ | 6″ | 7″ | 8″ |
Inch Fraction Division Chart
| ÷ 2 | ÷ 3 | ÷ 4 | ÷ 5 | ÷ 6 | ÷ 7 | ÷ 8 | |
|---|---|---|---|---|---|---|---|
| 1/4″ | 1/8″ | 5/64″ | 1/16″ | 3/64″ | 1/32″ | 1/32″ | 1/64″ |
| 1/2″ | 1/4″ | 11/64″ | 1/8″ | 7/64″ | 5/64″ | 1/16″ | 1/16″ |
| 3/4″ | 3/8″ | 1/4″ | 3/16″ | 5/32″ | 1/8″ | 7/64″ | 3/32″ |
| 1″ | 1/2″ | 21/64″ | 1/4″ | 13/64″ | 11/64″ | 9/64″ | 1/8″ |
Inch Fraction and Decimal Equivalents
