Drawing & geometry
Feet, inches & construction units
Add mixed feet-and-inch lengths and convert length, area, volume and mass.
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What a feet and inches calculator does
A feet and inches calculator adds or subtracts lengths written the way builders write them, such as 12' 7 3/8", and returns the answer in feet and inches to the fraction precision you choose (1/16 in by default, or 1/8, 1/32 and 1/64), in decimal feet, in metres and in millimetres. It reads fractions exactly, so nothing is rounded until the final display. A running tape mode adds or subtracts any number of lengths, and an area and volume mode multiplies feet-and-inch dimensions into square feet, cubic yards and their metric equivalents.
It also converts single values between construction units in four more modes: length (m, mm, cm, ft, in, yd), area (m², ft², yd², hectares, acres), volume (m³, ft³, yd³, litres, US gallons) and mass (kg, tonnes, lb, US tons). Each mode shows the value in every unit of that kind at once.
Use it to total a run of cabinet widths, convert a tape measurement for a metric drawing, turn decimal feet from a survey or CAD file into feet and inches you can mark out, or convert cubic yards of concrete to cubic metres.
How to use the feet, inches & construction units
- Choose a Calculation mode: Feet & inches, Running tape, Area & volume, Length, Area, Volume or Mass. The feet-and-inch modes share a Fraction precision of 1/8, 1/16, 1/32 or 1/64 in.
- In Feet & inches mode, type Length A in the form 5' 6 1/2", choose Add or Subtract, and type Length B. Decimal feet such as 10.375 are also accepted.
- In Running tape mode, add one row per length with Add or Subtract; the table shows each length and the running total, and the results give the final total.
- In Area & volume mode, enter a length and width in feet and inches, and a height or depth (0 for area only) to get square feet, square yards and square metres, plus cubic feet, cubic yards and cubic metres.
- Read lengths in feet and inches to the selected precision, decimal feet, metres and millimetres. In the unit modes, enter a value and pick its unit to see every unit of the same kind; the Imperial and Metric switch sets which unit is selected by default.
- Export the result as PDF or CSV (the CSV keeps full decimals), or copy it.
Worked example
5′ 6½″ + 2′ 3¼″ = 7′ 9¾″, or 2.38125 m.
How to add and subtract feet and inches
Add the feet and the inches separately, then carry every 12 in into a foot. Fractions work the same way: put them over a common denominator (usually 16) and carry every 16/16 into an inch.
Worked addition: 8' 4 5/8" + 3' 10 7/8". The fractions make 12/8, which is 1 1/2 in; the inches make 4 + 10 + 1 = 15 in, which is 1 ft 3 in. The total is 12' 3 1/2". The calculator returns 12' 3 1/2", 12.2917 ft or 3,746.5 mm.
Subtraction is where mistakes happen, because you often have to borrow. Worked example: 12' 7 3/8" − 4' 9 11/16". Convert 3/8 to 6/16. You cannot take 11/16 from 6/16, so borrow 1 in: 12' 6 22/16". You cannot take 9 in from 6 in, so borrow 1 ft: 11' 18 22/16". Now subtract: 7' 9 11/16". The calculator gives the same result, 7.8073 ft or 2,379.66 mm.
Fractions of an inch to decimals and millimetres
US tape measures are usually marked to 1/16 in, and the calculator rounds its feet-and-inches result to the nearest 1/16 in (1.5875 mm) unless you choose 1/8, 1/32 or 1/64 in. The chart converts each sixteenth to a decimal inch and to millimetres, using 1 in = 25.4 mm exactly.
| Fraction | Decimal inch | Millimetres |
|---|---|---|
| 1/16 | 0.0625 | 1.59 |
| 1/8 | 0.1250 | 3.18 |
| 3/16 | 0.1875 | 4.76 |
| 1/4 | 0.2500 | 6.35 |
| 5/16 | 0.3125 | 7.94 |
| 3/8 | 0.3750 | 9.53 |
| 7/16 | 0.4375 | 11.11 |
| 1/2 | 0.5000 | 12.70 |
| 9/16 | 0.5625 | 14.29 |
| 5/8 | 0.6250 | 15.88 |
| 11/16 | 0.6875 | 17.46 |
| 3/4 | 0.7500 | 19.05 |
| 13/16 | 0.8125 | 20.64 |
| 7/8 | 0.8750 | 22.23 |
| 15/16 | 0.9375 | 23.81 |
Inches to decimal feet chart
CAD, survey and estimating software often work in decimal feet, while tapes and drawings use feet and inches. Divide inches by 12 for decimal feet; multiply the decimal part of a foot by 12 for inches. 10.375 ft is 10 ft plus 0.375 × 12 = 4.5 in, or 10' 4 1/2".
| Inches | Decimal feet | Millimetres |
|---|---|---|
| 1 | 0.0833 | 25.4 |
| 2 | 0.1667 | 50.8 |
| 3 | 0.2500 | 76.2 |
| 4 | 0.3333 | 101.6 |
| 5 | 0.4167 | 127.0 |
| 6 | 0.5000 | 152.4 |
| 7 | 0.5833 | 177.8 |
| 8 | 0.6667 | 203.2 |
| 9 | 0.7500 | 228.6 |
| 10 | 0.8333 | 254.0 |
| 11 | 0.9167 | 279.4 |
| 12 | 1.0000 | 304.8 |
Decimal feet to feet and inches
Going the other way, tenths of a foot rarely land on a tape mark. The table rounds each value to the nearest 1/16 in, the same rounding the calculator displays.
| Decimal feet | Exact inches | Nearest 1/16 in |
|---|---|---|
| 0.1 | 1.2 | 1 3/16 |
| 0.2 | 2.4 | 2 3/8 |
| 0.25 | 3.0 | 3 |
| 0.3 | 3.6 | 3 5/8 |
| 0.4 | 4.8 | 4 13/16 |
| 0.5 | 6.0 | 6 |
| 0.6 | 7.2 | 7 3/16 |
| 0.7 | 8.4 | 8 3/8 |
| 0.75 | 9.0 | 9 |
| 0.8 | 9.6 | 9 5/8 |
| 0.9 | 10.8 | 10 13/16 |
Exact conversion factors the calculator uses
The calculator uses exact definitions rather than rounded factors. The US survey foot, about 2 parts per million longer than the international foot, was retired at the end of 2022. Older land surveys may still use it, but the difference does not matter at building scale.
- 1 ft = 0.3048 m and 1 in = 25.4 mm, both exact.
- 1 yd = 0.9144 m; 1 yd² = 9 ft² = 0.836 m²; 1 yd³ = 27 ft³ = 0.7646 m³, or 764.55 L.
- 1 m² = 10.764 ft²; 1 acre = 43,560 ft² = 4,046.86 m² = 0.4047 ha.
- 1 US gallon = 3.785 L, so 1 yd³ = 201.97 US gal.
- 1 lb = 0.45359237 kg exactly; 1 kg = 2.2046 lb; 1 US ton = 2,000 lb = 907.18 kg.
Who it is for and when to use it
Totaling cabinet, trim and material runs
Add fractional dimensions one pair at a time without converting to decimals on paper.
Moving between metric drawings and imperial tapes
Convert millimetre dimensions from product data or overseas drawings into feet and inches you can mark out, and back again.
Reading survey and CAD output
Turn decimal-foot distances and elevations into feet, inches and sixteenths.
Converting quantities for ordering
Change cubic yards to cubic metres, square feet to square metres, or pounds to kilograms when suppliers and drawings use different systems.
Method, formulas & assumptions
Mixed fractions are parsed as exact numerator/denominator values before conversion. International foot = 0.3048 m; inch = 0.0254 m; pound = 0.45359237 kg. Running tape adds or subtracts each row and reports the running total; area = length × width and volume = area × height from feet-and-inch inputs.
Imperial inputs are converted with exact factors (1 ft = 0.3048 m, 1 lb = 0.45359237 kg, 1 US gal = 3.785411784 L) before the calculation runs in SI, then results are converted back.
Common mistakes to avoid
- Typing a bare number and expecting inches. In feet-and-inches mode, 6 means 6 ft; type 6" for inches.
- Writing a dash between feet and inches. Enter 5' 6", not 5'-6"; the dash is not accepted.
- Confusing 6.5 with 6 1/2. A decimal on its own is read as feet (6.5 ft = 6' 6"), while 6 1/2 is read as inches.
- Reading 0.1 ft as 1 in. It is 1.2 in, closest to 1 3/16 in; decimal feet and inches do not line up.
- Rounding each step of a long sum. Keep fractions exact and round once at the end, as the calculator does.
- Mixing US and imperial (UK) gallons. The calculator uses the US gallon, 3.785 L; an imperial gallon is 4.546 L.
Scope & limits
In feet-and-inches modes use 5' 6 1/2" or a decimal feet value. Displayed fractional inches are rounded to the selected precision (1/8 to 1/64 in); CSV retains decimal values.
Frequently asked questions
How do I add feet and inches?
Add feet to feet and inches to inches, then carry every 12 in into a foot. For example, 8' 4 5/8" + 3' 10 7/8" = 12' 3 1/2".
How do I convert decimal feet to feet and inches?
Keep the whole feet and multiply the decimal part by 12 for inches. 10.375 ft is 10 ft plus 0.375 × 12 = 4.5 in, or 10' 4 1/2".
How do I convert inches to decimal feet?
Divide the inches by 12. 7 in is 0.5833 ft and 9 in is 0.75 ft.
What is 5/8 inch in millimetres?
5/8 in is 15.875 mm, usually rounded to 15.9 mm. Multiply any inch value by 25.4 to get millimetres.
How many millimetres is 1/16 inch?
1/16 in is 1.5875 mm. At the default 1/16 in precision a displayed feet-and-inches value is within about 0.8 mm of the exact figure; at 1/64 in it is within about 0.2 mm.
How many cubic metres are in a cubic yard?
One cubic yard is 27 ft³, which is 0.7646 m³ or 764.55 litres.
How many square feet are in a square metre?
One square metre is 10.764 ft², and one square foot is 0.0929 m².
What format should I type feet and inches in?
Use 5' 6 1/2" with spaces and no dash, inches alone as 18", or a decimal number of feet such as 5.5. Straight and curly foot and inch marks both work.
Do I need an account to download the result?
No. All calculations, local file processing and exports on this page are free, without an account.
Where are my inputs stored?
The tool keeps inputs in this browser tab. It does not upload them or create a cloud copy. Save or download anything you want to keep before leaving the page. Standard site analytics may operate independently of the tool.
Can I work in metric instead of imperial?
Yes. Use the Imperial / Metric switch above the inputs. Imperial (feet, inches, pounds, gallons) is the default; switching converts every dimensional field and result, and your choice is remembered across the free tools in this browser.
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