Add, subtract, multiply, and divide measurements in feet and inches — with real fractional-inch precision — then convert the answer to decimal feet, total inches, meters, or centimeters. Built for woodworking, framing, and CAD.
Round to nearest:
Measurements
Try:
Result
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The combined measurement in feet and inches.
Decimal feet—
Total inches—
Meters—
Centimeters—
Enter at least one measurement to see the result, with decimal-feet and metric conversions.
On a tape measure
Where the result lands within its foot, marked to the nearest fraction.
Feet & inches → everything else
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Decimal feet
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Total inches
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Meters
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Centimeters
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Millimeters
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Enter a measurement to convert it to decimal feet, total inches, and metric units.
Reverse: decimal → feet & inches
Have a decimal value from a drawing or spreadsheet? Convert it back to a tape-measure reading.
Feet & inches:—
Scale a measurement
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Try:
Result
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The scaled measurement in feet and inches.
Decimal feet—
Total inches—
Meters—
Enter a measurement and a multiplier to scale it up or down.
Measurements in feet and inches resist ordinary arithmetic: you can't just add 5'6" and 2'9" on a calculator, because inches carry into feet at 12 and fractions carry into inches at 16.
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Walk-through
How to Use This Calculator
3 steps▸
1
Pick what you want to do
Choose a tab: <strong>Arithmetic</strong> to add or subtract a list of measurements, <strong>Convert</strong> to turn one feet-inch measurement into decimal feet or metric (or back again), and <strong>Multiply / Divide</strong> to scale a measurement by a number. Set the rounding precision (1/2" down to 1/32") at the top — every result snaps to that nearest fraction.
2
Enter your measurements
Each measurement has three boxes: feet, inches, and a fraction-of-an-inch dropdown (1/16, 1/8, 1/4 …). Leave any box blank for zero. On the Arithmetic tab, press “Add another measurement” to stack as many rows as you need, then choose Add or Subtract. Everything recalculates instantly as you type — there is no Calculate button.
3
Read the answer every way you need it
The headline shows the result as feet, inches, and a reduced fraction (e.g. 8' 3-1/2"). Below it you get decimal feet (for CAD and spreadsheets), total inches, and metric (meters and centimeters). The tape-measure graphic shows where the fractional inch lands. Use Copy, CSV, or Share to take the result with you.
Every measurement is first reduced to a single number of inches. 5 ft 7-1/2 in = 5×12 + 7 + 0.5 = 67.5 inches. All arithmetic happens on this value, so fractions never drift.
Convert inches to other units
decimal_feet = total_in ÷ 12; meters = total_in × 0.0254; cm = total_in × 2.54; mm = total_in × 25.4
One inch is defined as exactly 0.0254 meters, so the metric conversions are exact, not approximate. Decimal feet is simply total inches divided by 12.
Round back to a tape-measure fraction
units = round(total_in × P); fraction = (units mod P) ÷ P, reduced
P is the chosen precision denominator (2, 4, 8, 16, or 32). The result is rounded to the nearest 1/P inch, then the fraction is reduced to lowest terms (8/16 → 1/2) and any carry rolls up through inches and feet.
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Glossary
Key Terms Explained
5 terms▸
Decimal feetA length expressed as feet with a decimal instead of separate inches — 5.625 ft instead of 5 ft 7-1/2 in. Used by CAD software, surveyors, and spreadsheets because it is easier to multiply and add.
Fractional inchThe sub-inch part of a measurement written as a fraction (1/2, 3/16, 7/8) rather than a decimal. Tape measures are marked in fractions, usually down to 1/16 inch, sometimes 1/32.
Improper fractionA fraction whose numerator is at least as large as its denominator, like 18/16. This calculator never displays one — it carries the whole part up into inches (18/16 in = 1-1/8 in).
Precision (rounding denominator)How finely the answer is rounded: 1/16 means the result snaps to the nearest sixteenth of an inch. Finer precision (1/32) keeps more detail; coarser (1/4) matches what you can actually read on a rough tape.
Nominal vs. actual sizeLumber and other materials are sold under a 'nominal' name that differs from the real measurement: a '2×4' is actually 1-1/2 in × 3-1/2 in. Always enter the actual size when doing real math — this calculator works in true inches.
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Scenarios
Real-World Examples
3 worked examples▸
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Trim carpenter
Adding two cut pieces of baseboard
Piece 1 5 ft 6 inPiece 2 2 ft 9 in
On the Arithmetic tab with Add selected, the total is 8' 3" — that's 99 total inches, 8.25 decimal feet, or 2.515 m. Because both pieces are whole inches, no fraction appears. This is the everyday 'how long is the run?' calculation.
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Cabinet maker
Subtracting a reveal from an opening
Opening 8 ft 0 inMinus 1 ft 4-1/2 in
Switch to Subtract: 8' 0" − 1' 4-1/2" = 6' 7-1/2". The calculator handles the borrow across the foot boundary for you and keeps the half-inch exact. If you subtract a larger value from a smaller one, you get a clean negative result (e.g. −1' 0").
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CAD drafter
Converting a tape reading for a drawing
Measurement 5 ft 7-1/2 inNeed decimal feet + meters
On the Convert tab, 5' 7-1/2" reads out as 5.625 decimal feet, 67.5 total inches, 1.715 m, and 171.45 cm. Drop the 5.625 straight into your model. The reverse box turns a decimal back into a tape reading — type 5.625 ft and it shows 5' 7-1/2".
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Deep Dive
Working in Feet, Inches, and Fractions Without the Headaches
Measurements in feet and inches resist ordinary arithmetic: you can't just add 5'6" and 2'9" on a calculator, because inches carry into feet at 12 and fractions carry into inches at 16. This tool does the carrying for you — and converts the answer to decimal feet or metric whenever you need a different form.
How the calculator works
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Internally, every measurement is collapsed into a single value: total inches. Feet are multiplied by twelve, whole inches are added, and the fraction (numerator over denominator) is added on top. All addition, subtraction, multiplication, and division happen on that one number, so fractions never accumulate rounding error during the math.
Only at the very end is the answer turned back into feet, inches, and a fraction. The tool rounds to your chosen precision — the nearest 1/16 inch by default — reduces the fraction to lowest terms, and rolls any overflow up through inches and feet so you never see something like 14/16 or 13 inches.
Inputs and what they mean
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Feet, inches, and fraction make up one measurement. Leave any field blank to treat it as zero, so a pure-inch value like 7-1/2" just needs the inches and fraction boxes. Precision controls how fine the rounding is — match it to your tape (most read to 1/16, fine work to 1/32). Operation (Add / Subtract on the Arithmetic tab, Multiply / Divide on the third tab) sets what happens to the list of measurements.
The Convert tab also has a reverse box: give it a decimal value and a unit — decimal feet, inches, meters, centimeters, or millimeters — and it returns the nearest tape-measure reading. That is the fastest way to turn a number off a drawing back into something you can mark on a board.
Limits and edge cases
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Subtracting a larger measurement from a smaller one returns a negative reading, shown with a leading minus sign — useful for checking which piece is longer. Dividing by zero is undefined, so the calculator asks for a non-zero divisor instead of showing a result. Rounding to a coarse precision can make the displayed fraction look slightly off the exact math (for example, 1/3 of an inch has no exact sixteenth); switch to 1/32 for more detail, or read the decimal-feet figure for the exact value.
Finally, remember the nominal-versus-actual trap: dimensional lumber, pipe, and sheet goods are named by sizes that differ from their true measurements. Enter the real dimensions and this calculator will be exact.
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Questions
Frequently Asked Questions
7 questions▸
How do I add feet and inches together?+
Use the Arithmetic tab with Add selected. Enter each length in its own row — feet, inches, and a fraction if needed — and press 'Add another measurement' for more rows. The total appears instantly as feet-inches-fraction, plus decimal feet and metric. Example: 5'6" + 2'9" = 8'3".
How do I convert feet and inches to decimal feet?+
Divide total inches by 12, or just use the Convert tab. It shows decimal feet automatically: 5 ft 7-1/2 in is 5.625 decimal feet. Decimal feet is what CAD programs and spreadsheets expect, since it can be added and multiplied like any ordinary number.
How accurate are the fraction results?+
The math is done in exact inches, so the only rounding happens when the answer is displayed as a fraction — to whatever precision you pick (1/2" through 1/32"). For a value that has no exact fraction at that precision, the calculator shows the nearest one and you can read the exact figure from the decimal-feet or total-inches output.
Can it handle negative results when subtracting?+
Yes. If you subtract a longer measurement from a shorter one, the result is shown with a leading minus sign — for example 2' 0" − 3' 0" = −1' 0". That makes it easy to see which piece is longer and by how much.
What units can it convert to and from?+
From feet-and-inches it gives decimal feet, total inches, meters, centimeters, and millimeters. The reverse box goes the other way: enter a decimal value in any of those units and it returns the nearest feet-inch-fraction reading. One inch is exactly 2.54 cm, so the metric conversions are exact.
Why does a '2x4' not measure 2 inches by 4 inches?+
Those are nominal sizes — the name the lumber is sold under, not its real dimensions. A finished 2×4 is actually 1-1/2" × 3-1/2". Always enter the actual measured size when calculating, and this tool will give you an exact answer.
Can I share or save a calculation?+
Yes. The Share button copies a link that reopens the calculator on the same tab and settings, and your inputs are also remembered in your browser between visits. Copy puts a plain-text summary on your clipboard, and CSV downloads the result with all unit conversions.
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Save & share
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Calculations use total inches internally. Tape-measure values are rounded to the selected fraction, from the nearest 1/2 inch through the nearest 1/32 inch. Metric conversions use the exact definition of 1 inch = 0.0254 meters.
Last verified: June 2026. Next review: June 2027.
For structural, engineering, fabrication, or safety-critical work, verify measurements against project specifications and applicable professional standards.