Feet and Inches Calculator Online: Add, Subtract, Convert

This online feet and inches calculator lets you add, subtract, multiply, and divide measurements that are in feet and inches, and it also converts between feet/inches and decimal feet or meters. You enter values like 5 ft 6 in or 6 ft 8 in, pick an operation, and the calculator returns the result in feet and inches, decimal feet, and inches. It is built for construction, woodworking, sewing, and any project where measurements come in the imperial system.

Formula

The calculator works by converting everything to inches first, doing the math in inches, then converting back to feet and inches. The core formulas are:

• Convert to inches: total_inches = (feet × 12) + inches
• Add: result_inches = total_inches_1 + total_inches_2
• Subtract: result_inches = total_inches_1 − total_inches_2
• Multiply: result_inches = total_inches_1 × total_inches_2 (this gives square inches if both are lengths, but the calculator treats it as a pure number)
• Divide: result_inches = total_inches_1 ÷ total_inches_2 (a dimensionless ratio)

Then to convert back: feet = floor(result_inches / 12) and remaining inches = result_inches − (feet × 12). For metric output, 1 inch = 0.0254 meters exactly.

Worked Example

Using the default values: first value = 5 ft 6 in, second value = 3 ft 9 in, operation = Add.

1. Convert first value to inches: (5 × 12) + 6 = 60 + 6 = 66 inches
2. Convert second value to inches: (3 × 12) + 9 = 36 + 9 = 45 inches
3. Add: 66 + 45 = 111 inches
4. Convert back to feet and inches: 111 ÷ 12 = 9 feet with remainder 3 inches
5. Result: 9 ft 3 in, which equals 9.25 decimal feet or 2.8194 meters

That matches the calculator output for the default inputs.

Why Use Feet and Inches Instead of Decimals?

In the US, construction lumber, drywall, and many hardware items are sold in feet and inches. A 2×4 stud is actually 1.5 by 3.5 inches, and a sheet of plywood is 4 ft by 8 ft. When you measure a wall, you might get 12 ft 7 in, not 12.583 ft. Using feet and inches avoids rounding errors that come from converting to decimal feet too early. For example, 7 inches is 0.5833 feet, and if you round to 0.58, you lose about 0.04 inches per measurement—small, but it adds up over a long run of framing.

Common Mistakes and How to Avoid Them

• Forgetting to carry the 12: When adding 8 in + 7 in, you get 15 in, which is 1 ft 3 in. Many people write 15 in and forget to convert.
• Mixing units in subtraction: 5 ft 2 in − 3 ft 9 in requires borrowing: 5 ft 2 in = 4 ft 14 in, then subtract 3 ft 9 in = 1 ft 5 in.
• Using decimal feet when you need fractions: 0.5 ft is 6 in, but 0.33 ft is not exactly 4 in (it is 3.96 in). Always convert using ×12 for inches.
• Ignoring negative results: If you subtract a larger measurement from a smaller one, the result is negative. This calculator shows it as negative inches and negative feet/inches.

How to Read the Results

The first output, Total inches, is the raw result in inches—useful for ordering materials that are sold by the inch, like trim or piping. The second output, Feet and inches, is the same value broken into whole feet and remaining inches, which is how you would mark it on a tape measure. Decimal feet is the result as a single number, handy for entering into CAD software or a calculator that expects decimal input. Meters gives the metric equivalent, useful when working with imported plans or metric hardware.

When to Use This Calculator vs. a Regular Calculator

A regular calculator handles numbers fine, but it does not understand that 12 inches equals 1 foot. If you type 5.6 + 3.9, you get 9.5, which you then have to interpret as 9 ft 6 in—but only if you remember that 0.5 ft is 6 in. This calculator does that conversion automatically. It is especially useful for:

• Adding up multiple measurements for a single cut list (e.g., 3 pieces of 2 ft 4 in each)
• Finding the difference between two measurements to see how much material you need to remove
• Scaling a pattern up or down (multiply or divide)
• Converting a measurement from feet and inches to meters for international shipping or plans

Limitations and Edge Cases

This calculator works with whole inches and feet, so it does not handle fractional inches like 1/16 or 3/8. If you need fractions, convert them to decimals first (e.g., 3/8 in = 0.375 in) and enter that as the inches value. Also, multiplication of two lengths gives a result in square inches (area), not linear inches—this calculator returns a linear number, so it is best used for scaling, not area calculations. Division of two lengths gives a unitless ratio, which is useful for finding how many times one length fits into another.

Frequently Asked Questions

How do I convert 5 feet 6 inches to just inches?

Multiply the feet by 12 and add the inches: 5 × 12 = 60, plus 6 = 66 inches. This is the first step the calculator does internally.

What is 6 ft 3 in minus 2 ft 8 in?

Convert both to inches: 6 ft 3 in = 75 in, 2 ft 8 in = 32 in. Subtract: 75 − 32 = 43 in. Convert back: 43 ÷ 12 = 3 ft with remainder 7 in, so the answer is 3 ft 7 in.

How many inches are in a foot?

There are exactly 12 inches in 1 foot. This is the basis for all conversions in this calculator.

Can I use this for metric measurements?

This calculator is for feet and inches only. For metric, you would enter meters and centimeters separately, but the logic is the same: 100 cm = 1 m. The output includes meters as a conversion, but the inputs must be in feet and inches.

Why do I get a negative result when subtracting?

If the first measurement is smaller than the second, the difference is negative. For example, 2 ft − 3 ft = −1 ft. This is correct mathematically, but for physical measurements you would usually take the absolute value to get the distance between the two.

How do I multiply feet and inches by a whole number?

Enter the whole number as the feet value and 0 as the inches for the second measurement, then choose Multiply. For example, to triple 4 ft 5 in, enter 4 ft 5 in as the first value and 3 ft 0 in as the second, and the result is 13 ft 3 in.

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in ft1 | Feet (first value) | ft | 5 | 0
in in1 | Inches (first value) | in | 6 | 0
in ft2 | Feet (second value) | ft | 3 | 0
in in2 | Inches (second value) | in | 9 | 0
sel op | Operation | Add=1, Subtract=2, Multiply=3, Divide=4
out total_in | Total inches | in | (ft1*12+in1) + (ft2*12+in2) * (op==2 ? -1 : 1) * (op==3 ? (ft2*12+in2) : 1) / (op==4 ? (ft2*12+in2) : 1) | 2
out ft_in | Feet and inches | - | floor(total_in/12) + " ft " + round(total_in - floor(total_in/12)*12, 0) + " in" | 0
out decimal_ft | Decimal feet | ft | total_in / 12 | 2
out meters | Meters | m | total_in * 0.0254 | 2