Your result
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Enter your values, then click Calculate result.How this calculator helps
Add or subtract two mixed feet-and-inches lengths, with normalized signed output, total inches, decimal feet and metres. Enter feet and inches in separate fields for each length. These fields represent components of one measurement, not two unrelated measurements. A blank component is not assumed to be zero: enter an explicit zero when one part is absent. Components must be nonnegative finite numbers. Fractional inches are accepted as decimals, so a half inch is 0.5, not the unparsed expression 1/2.
How to use it
- 1
Choose the correct input basis for feet and inches calculator and enter the values described below. The demonstration defaults are examples, not independently verified personal measurements.
- 2
Review add or subtract before submitting. Match the selected units and roles to the original source record, including any signs or percentage conventions.
- 3
Click Calculate result to submit the current inputs. Editing a field preserves the previous submitted output until you calculate again; the status message identifies that pending change.
- 4
Compare the labeled result with the worked example and independent verification checks. Review using a dimensional result before copying it into another worksheet.
Formula and methodology
Total inches = 12f₁+i₁ ± (12f₂+i₂). Convert the absolute result back with whole feet = floor(|inches|/12); residual inches = |inches|−12×whole feet.
The calculator applies the displayed arithmetic to the values entered on this device. It does not silently load a local tax rate, currency conversion or commercial assumption.
Worked calculation example
5 ft 8 in plus 2 ft 7 in equals 99 inches, normalized to 8 ft 3 in. Decimal feet are 8.25 and metres are 2.5146. Subtracting 2 ft 7 in from 5 ft 8 in gives 37 inches, or 3 ft 1 in. Inches are carried or borrowed through the total-inch representation.
How to interpret your result
The inch fields may exceed twelve because normalization happens after the operation. Entering zero feet and twenty inches represents one foot eight inches. A negative result is displayed with a minus sign applying to the entire mixed length, not only its feet component. Thus minus one foot three inches means minus fifteen total inches. The total-inch row removes ambiguity when copying a signed result.
For different inputs or formulas, use Length Conversion Calculator; Square Footage Calculator.
Related questions this calculator covers
- inches to feet calculator
- feet and inches calculator
- inch calculator
- feet inches calculator
Scenario comparison
| Scenario | What it shows |
|---|---|
| Carry | 1 ft 10 in plus 0 ft 5 in gives 2 ft 3 in. |
| Borrow | 2 ft 1 in minus 0 ft 5 in gives 1 ft 8 in. |
| Negative | zero minus 1 ft 3 in gives −15 inches. |
Common mistakes to avoid
- Writing mixed feet and inches as decimal feet.
- Applying a minus sign only to the feet component.
- Forgetting to supply explicit zero components.
Convert each input to total inches manually, perform the operation, then divide by twelve for decimal feet. Recombine normalized absolute feet and inches and apply the whole-result sign. Adding the second length back to a subtraction result should recover the first. Metres should equal total inches multiplied by 0.0254.
Authoritative reference. Method references reviewed on 5 October 2026. SolvePilot supplies the original examples and bounded browser implementation. Review by Mohammad Qasim covers editorial scope and arithmetic, not individual professional approval. The cited reference provides method or unit context rather than certifying the entered measurements or assumptions.What can affect the result?
Mixed-length entries
Enter feet and inches in separate fields for each length. These fields represent components of one measurement, not two unrelated measurements. A blank component is not assumed to be zero: enter an explicit zero when one part is absent. Components must be nonnegative finite numbers. Fractional inches are accepted as decimals, so a half inch is 0.5, not the unparsed expression 1/2.
Add or subtract
Choose the operation before calculating. Subtraction means first complete length minus second complete length. Swapping measurements reverses the sign for subtraction but preserves the total for addition. The calculation first converts each mixed length to inches, performs the chosen operation and then normalizes the result. This avoids hand-carry mistakes when the inch sum exceeds twelve or when subtraction requires borrowing.
Normalization and sign
The inch fields may exceed twelve because normalization happens after the operation. Entering zero feet and twenty inches represents one foot eight inches. A negative result is displayed with a minus sign applying to the entire mixed length, not only its feet component. Thus minus one foot three inches means minus fifteen total inches. The total-inch row removes ambiguity when copying a signed result.
Decimal feet are different
8 ft 3 in equals 8.25 decimal feet because three inches is one quarter foot. It is not 8.3 feet. The supporting decimal-foot result is useful when a separate worksheet expects one scalar length. The metre conversion uses the international inch definition of 0.0254 m. No survey-foot, architectural drawing scale or physical tolerance is inferred from the entered dimensions.
Using a dimensional result
For trim, layouts or material planning, this page performs length arithmetic only. It does not add saw kerf, seams, waste, shrinkage or installation allowances. The components are individually bounded to 10¹² and ordinary floating-point precision applies to fractional values. For long repeated decimal sums, retain the total-inch representation and round only at the stage required by the actual measurement process.
Privacy and browser processing
Values entered on this page are processed in the current browser session. SolvePilot does not require an account and does not receive the values entered into the calculator. Refreshing or closing the page clears the working values unless the browser itself restores a previous session. Avoid entering identifying or account information because the calculation needs summary values only.
Accuracy and verification
Accuracy depends first on input quality. Confirm definitions, scales, dates and source information before entering a value. Keep an independent record of any result used for planning because this page does not create an official statement or retain a calculation history.
Limits of this estimate
For trim, layouts or material planning, this page performs length arithmetic only. It does not add saw kerf, seams, waste, shrinkage or installation allowances. The components are individually bounded to 10¹² and ordinary floating-point precision applies to fractional values. For long repeated decimal sums, retain the total-inch representation and round only at the stage required by the actual measurement process.
Sources and review information
Frequently asked questions
Can inches be greater than twelve?＋
Yes. The result normalizes them into additional feet plus a remaining inch amount.
Can I enter half inches?＋
Yes, as 0.5. Fraction expressions such as 1/2 are not parsed.
What does a negative mixed result mean?＋
The sign applies to the whole length. The total-inch row shows the same signed value explicitly.
Is 5.8 feet five feet eight inches?＋
No. Decimal feet and mixed notation differ. Five feet eight inches is 5.666667 decimal feet approximately.
Does it include cutting waste?＋
No. It only combines the supplied lengths. Allowances need a separately established calculation.