Feet and Inches Calculator

Construction-length workbench

Calculate, normalize, and convert feet and inches

Work with separate feet, whole inches, and binary inch fractions, or convert a decimal or metric length in either direction.

Solve forRound fractional inches toDecimal places

Operation

Enter two lengths, then choose Add or Subtract.

First length

FeetWhole inchesInch fraction

Second length

FeetWhole inchesInch fraction

Mixed-unit construction arithmetic

Calculate with feet, inches, and shop fractions without notation traps

Feet-and-inches measurements use twelve inches per foot and often divide the inch into binary fractions. Reliable arithmetic starts by normalizing that mixed notation, then rounds only the final construction-style result.

Step-by-step guide · Mixed-unit construction arithmetic

Normalize arithmetic before formatting the answer

Mixed-unit base: 12 in = 1 ft
Exact metric bridge: 1 in = 25.4 mm
Supported finish: Nearest 1/2 through 1/64 in

Convert both lengths to a common internal unit
Five feet nine inches is 69 inches. Two feet seven and three-eighths inches is 31.375 inches. A common unit prevents separate foot, inch, and fraction columns from drifting out of alignment.
Perform the operation once
Adding those examples gives 100.375 inches. Subtraction can produce a negative result, and division must reject a zero divisor rather than guessing a value.
Return to normalized notation
100.375 inches becomes 8 ft 4 3/8 in. Carrying from twelve inches into one foot occurs only after the underlying arithmetic is complete.

Calculate with feet, inches, and shop fractions without notation traps: Feet-and-inches measurements use twelve inches per foot and often divide the inch into binary fractions. Reliable arithmetic starts by normalizing that mixed notation, then rounds only the final construction-style result.

Feet and inches are mixed-radix notation, not a decimal number

In a measurement such as 5 ft 9 in, the inch component counts twelfths of a foot. It is not the decimal part of 5.9 ft. Five feet nine inches equals 5.75 decimal feet, while 5.9 decimal feet equals 5 ft 10.8 in. Treating the separator as a decimal point creates an error before any addition or conversion begins.

Construction fractions add another layer. One-half, one-quarter, one-eighth, and one-sixteenth inch are binary subdivisions used by many tape measures and shop drawings. The workbench converts every entered length to one internal total, performs the requested arithmetic, and then normalizes the result back into a sign, feet, whole inches below twelve, and a reduced fraction.

Normalize arithmetic before formatting the answer

Convert both lengths to a common internal unit
Five feet nine inches is 69 inches. Two feet seven and three-eighths inches is 31.375 inches. A common unit prevents separate foot, inch, and fraction columns from drifting out of alignment.
Perform the operation once
Adding those examples gives 100.375 inches. Subtraction can produce a negative result, and division must reject a zero divisor rather than guessing a value.
Return to normalized notation
100.375 inches becomes 8 ft 4 3/8 in. Carrying from twelve inches into one foot occurs only after the underlying arithmetic is complete.

Fractional rounding is a field decision

Unrounded total

Keep this value for decimal inches, decimal feet, yards, and metric equivalents. It preserves the calculation before presentation choices.

Construction fraction

Choose the nearest half, quarter, eighth, sixteenth, thirty-second, or sixty-fourth inch for the final mixed display. The selected denominator should reflect the tool, material, and tolerance actually in use.

Manufacturing tolerance

Rounding a nominal dimension is not the same as defining an allowable tolerance. The calculator does not decide whether a rounded cut remains acceptable.

Bridge to metric and project quantities deliberately

A resolved decimal-foot measurement can go to the feet-to-metres calculator for a metric deliverable. If the job begins with a metric plan, the metres-to-feet calculator explains decimal-foot output before mixed notation is chosen. Small hardware dimensions belong in the millimetres-to-inches calculator.

This page calculates linear measurements. Surface size belongs in the area calculator, and lumber volume and pricing conventions belong in the board-foot calculator. The exact international inch and foot definitions support metric conversion, but they do not turn rough field measurements into precise plans or replace a project's dimensioning standard.

Important limitations

Mixed-length fields treat feet and whole inches as components of an absolute input length; subtraction or a signed decimal/scalar can produce a negative result. Fractional-inch precision affects only the final construction measurement, while decimal precision affects only supporting displays. The calculator does not parse free-form dimension strings or calculate area or volume.

Review the stated scope, calculation method, assumptions, supported inputs, and effective dates, and obtain qualified advice before using a high-stakes result.

This formula passed its registered engineering tests and is published under an explicit site-owner policy authorization. No independent expert, QA, editorial, legal, or third-party review is claimed. Verify consequential results with a qualified professional.

Mixed-unit construction arithmetic

Calculate with feet, inches, and shop fractions without notation traps

Step-by-step guide · Mixed-unit construction arithmetic

Normalize arithmetic before formatting the answer

Mixed-unit base: 12 in = 1 ft
Exact metric bridge: 1 in = 25.4 mm
Supported finish: Nearest 1/2 through 1/64 in

Convert both lengths to a common internal unit
Five feet nine inches is 69 inches. Two feet seven and three-eighths inches is 31.375 inches. A common unit prevents separate foot, inch, and fraction columns from drifting out of alignment.
Perform the operation once
Adding those examples gives 100.375 inches. Subtraction can produce a negative result, and division must reject a zero divisor rather than guessing a value.
Return to normalized notation
100.375 inches becomes 8 ft 4 3/8 in. Carrying from twelve inches into one foot occurs only after the underlying arithmetic is complete.

Feet and inches are mixed-radix notation, not a decimal number

Normalize arithmetic before formatting the answer

Convert both lengths to a common internal unit
Five feet nine inches is 69 inches. Two feet seven and three-eighths inches is 31.375 inches. A common unit prevents separate foot, inch, and fraction columns from drifting out of alignment.
Perform the operation once
Adding those examples gives 100.375 inches. Subtraction can produce a negative result, and division must reject a zero divisor rather than guessing a value.
Return to normalized notation
100.375 inches becomes 8 ft 4 3/8 in. Carrying from twelve inches into one foot occurs only after the underlying arithmetic is complete.

Fractional rounding is a field decision

Unrounded total

Keep this value for decimal inches, decimal feet, yards, and metric equivalents. It preserves the calculation before presentation choices.

Construction fraction

Manufacturing tolerance

Rounding a nominal dimension is not the same as defining an allowable tolerance. The calculator does not decide whether a rounded cut remains acceptable.

Convert both lengths to a common internal unit

Perform the operation once

Return to normalized notation

Feet and inches are mixed-radix notation, not a decimal number

Normalize arithmetic before formatting the answer

Fractional rounding is a field decision

Unrounded total

Construction fraction

Manufacturing tolerance

Bridge to metric and project quantities deliberately

Important limitations

Convert both lengths to a common internal unit

Perform the operation once

Return to normalized notation

Feet and inches are mixed-radix notation, not a decimal number

Normalize arithmetic before formatting the answer

Fractional rounding is a field decision

Unrounded total

Construction fraction

Manufacturing tolerance

Bridge to metric and project quantities deliberately