Introduction
This feet and inches calculator lets you add, subtract, multiply, and divide measurements the way they appear on a tape measure. Enter values in feet, inches, fractions, or decimals, and get results in every format you need, including metric. It handles mixed numbers like 4 1/8 and fractions like 3/16, so you don't have to convert anything by hand.
Use the structured mode to plug in two measurements and pick an operation. Or switch to free-form mode and type a full expression with feet, inches, centimeters, and millimeters all at once. The calculator rounds results to the fraction size you choose, from 1/2 inch down to 1/64 inch.
This tool saves time and removes math errors on the job site when you are framing walls, cutting trim, laying tile, or planning a build. It works on any phone, tablet, or computer, so you can use it right where you work.
How to Use Our Feet and Inches Calculator
Enter two measurements in feet and inches, pick a math operation, and this calculator gives you the answer in feet, inches, metric units, and more.
Input Mode: Choose "Structured Input" to type feet and inches into separate boxes. Choose "Free-Form Expression" to type a full math problem in one line, like 4' 3 7/8" + 1.25in.
Round to Nearest: Pick how precise you want the fractional inch result to be. For example, 1/8" works for most construction tasks. Choose 1/16" or smaller for finer work.
Measurement 1 – Feet: Enter the feet part of your first measurement. You can use whole numbers or decimals. Leave it blank if you only have inches.
Measurement 1 – Inches: Enter the inches part of your first measurement. You can type a decimal like 8.5, a fraction like 3/4, or a mixed number like 6 3/4.
Operation: Pick what math you want to do. Add, subtract, multiply, or divide two measurements. You can also multiply or divide by a plain number (factor), or just convert and round a single measurement.
Measurement 2 – Feet and Inches: Enter your second measurement the same way as the first. This box shows up when you pick add, subtract, multiply, or divide.
Factor: Enter a plain number to multiply or divide your first measurement by. This box shows up when you pick "Multiply by Factor" or "Divide by Factor." You can use decimals, fractions, or mixed numbers.
Free-Form Expression: Type a full math problem using feet (ft or '), inches (in or "), centimeters (cm), and millimeters (mm) with + and − signs. Numbers without a unit are read as inches.
Calculate: Press this button to get your answer. The result shows in feet and inches, decimal feet, total inches, millimeters, centimeters, and meters.
Reset: Press this button to clear all fields and start over with the default values.
More Precision: Click this button below the result to see more decimal places in the decimal and metric outputs.
Use Result as Input: Click this button to send your answer back into Measurement 1 so you can chain multiple calculations together without retyping.
How to Calculate Feet and Inches
Feet and inches are the standard units of length used in construction, woodworking, and building projects across the United States. One foot equals 12 inches. Most tape measures show inches broken into fractions like 1/2, 1/4, 1/8, and 1/16 of an inch. When you measure boards, walls, pipes, or any material on a job site, you usually get readings in feet, inches, and fractions.
Adding, subtracting, multiplying, or dividing these measurements by hand is tricky. Unlike regular numbers, inches only go up to 12 before they roll over into the next foot. Fractions need a common denominator before you can combine them. A small math mistake can lead to a bad cut, wasted material, or parts that do not fit together.
How Feet and Inches Math Works
To add two measurements, you first add the inches together. If the inches total 12 or more, you convert every 12 inches into one foot. For example, 5 ft 9 in plus 3 ft 7 in gives you 8 ft 16 in. Since 16 inches is more than 12, you take out 12 inches and add 1 foot. The answer is 9 ft 4 in.
Subtraction works the same way but in reverse. If you need to subtract more inches than you have, you borrow 1 foot (12 inches) and add it to your inch value first. Multiplying and dividing feet and inches is easier when you first convert everything into total inches, do the math, then convert back.
Working with Fractions on a Tape Measure
Tape measures split each inch into equal parts. The most common marks are at every 1/16 of an inch. The smallest lines on the tape are 1/16 marks. The next bigger lines are 1/8 marks. Then come 1/4, 1/2, and the full inch. When you read a tape measure, you count how many of the smallest marks past the last whole inch your measurement falls. A reading like 5 and 3/16 inches means the edge lands three small marks past the 5-inch line.
When you add or subtract fractions, you need to give them the same bottom number (denominator). For instance, to add 3/8 and 1/4, you change 1/4 to 2/8, then add to get 5/8. This calculator handles all of that for you and rounds the result to whichever fraction size you pick.
Converting Between Imperial and Metric Units
One inch equals exactly 25.4 millimeters. One foot equals 304.8 millimeters or 30.48 centimeters. These conversions matter when you work with materials or plans that use metric units. Many engineered products, tiles, and imported materials list sizes in millimeters or centimeters. Knowing how to go back and forth between systems helps you avoid ordering the wrong size.
Common Uses in Construction
Builders, carpenters, plumbers, and electricians use feet and inches math every day. You might need to add up wall lengths to figure out how much baseboard to buy. You might subtract a door opening from a total wall width. Dividing a board into equal parts requires dividing its total length by the number of pieces. Multiplying a measurement by a factor helps when you scale plans up or down. In each case, getting the fractions right saves time, money, and materials on the job.