Decimal Feet to Feet and Inches

How to convert decimal feet to feet and inches

The arithmetic is short enough to do in your head once you have seen it. The whole number in front of the decimal point is already feet, so leave it alone. Take everything after the point and multiply by 12, because there are twelve inches in a foot. That product is your inches.

5.75 ft  →  5 ft, and 0.75 × 12 = 9  →  5 ft 9 in

Clean examples like that one are the exception. Feed in a real measurement off a total station or a spreadsheet and the inches almost always come out with a decimal of their own. Take 12.3456 ft: the 12 stays as feet, then 0.3456 × 12 = 4.1472 inches. You cannot mark 0.1472 of an inch on a board, so that leftover has to be rounded to a fraction — and which fraction you choose changes the answer. At sixteenths it lands on 12 ft 4 1/8 in; at thirty-seconds it is 12 ft 4 5/32 in. Both are correct; they are answers to different questions about how precisely you intend to work.

Tenths of a foot are not inches — the error that costs money

This is the one thing worth taking away from this page. Survey and engineering drawings are dimensioned in decimal feet, usually to hundredths. Carpenters, fabricators and anyone holding a tape work in feet and inches. The two systems divide the foot differently — into ten parts and into twelve — and a decimal point looks identical in both.

So when a drawing says 0.4 ft and someone reads it as "4 inches", they are not making a silly mistake; they are making an extremely natural one. And they are wrong by 0.8 of an inch. Here is the full damage:

The error grows steadily and peaks just short of a full foot: 0.9 ft is 10.8 inches, but reading it as 9 inches is out by 1.8 inches. On a single stud that is an annoyance; run it across a foundation layout, a run of formwork or a set of shop drawings and it becomes rework. There is a useful sanity check that takes one second: a tenth of a foot is always slightly more than an inch and change — 1.2 in, to be exact. If your converted inches number is smaller than the tenths figure you started with, you have read the wrong scale.

The reason both systems survive is that each is better at its own job. Decimal feet add, subtract and average with plain arithmetic, which is what you want when you are chaining survey shots or computing a grade. Feet and inches divide neatly by 2, 3, 4 and 6, which is what you want when you are laying out framing. Engineering feet to inches is a translation step, not an upgrade — and it belongs at the last possible moment, right before someone cuts.

Rounding to a fraction your tape measure actually has

A tape measure does not have infinite resolution. Most US tapes are graduated to 1/16 in; joinery and machining work goes to 1/32 or finer; rough framing rarely needs better than 1/8. The converter above lets you pick, because the right precision is a property of the job, not of the number.

The way this tool rounds matters more than it sounds. It converts the leftover to a whole number of sixteenths (or halves, or thirty-seconds) first, and only then splits off the whole inches and feet. Doing it the other way round is how converters end up printing impossible results like "11 16/16 in": the fraction rounds up to a full inch but nothing carries it. Enter 5.9999 ft in the box above and you will get a clean 6 ft 0 in, which is what a person would say. Fractions are also reduced, so you see 1/2 rather than 8/16 and 3/4 rather than 24/32.

Converting feet and inches back to decimal feet

Going the other way is the same relationship rearranged, and it is the direction estimators need most — takeoffs, material schedules and spreadsheets all want a single decimal number. Add the fraction to the whole inches, divide the total by 12, then add the feet:

8 ft 9 3/4 in  →  9.75 ÷ 12 = 0.8125  →  8.8125 ft

The two constants worth memorising for this direction are that one inch is 0.083333 feet, not 0.1, and one sixteenth of an inch is 0.00520833 feet. That first one is the tenths trap seen from the opposite side, and it is why an inch-based measurement almost never produces a tidy decimal. Switch the converter to its second tab to do this direction, and note that it round-trips exactly: any feet-inches-fraction value converted to decimal and back returns the value you started with.

Quick reference: common decimal feet values

The feet-and-inches column above is rounded to the nearest 1/16, matching the converter's default. Notice how the values built from halves and quarters of a foot land exactly, while anything involving tenths does not — that is the ten-versus-twelve mismatch showing up again.

Why the foot is exactly 0.3048 metres — and why surveyors had a second one

The international foot has been defined as exactly 0.3048 metres since the 1959 agreement between the national standards bodies of the English-speaking countries, which set the yard at exactly 0.9144 m. That makes one inch exactly 25.4 mm, with no rounding anywhere in the chain — the millimetre column in the table above is exact, not approximate.

There is a wrinkle that matters if you work with older survey data. The United States kept a second, very slightly longer U.S. survey foot for land surveying, defined as 1200/3937 metres. The difference is about two parts per million — invisible over a room, but roughly two feet across a state plane coordinate grid, which is more than enough to misplace a property corner. NIST and NOAA deprecated the survey foot at the end of 2022, so all new work uses the international foot. If you are reading a plat from before then, check which foot it was drawn in before you trust the eighth decimal place.

Primary sources: NIST Special Publication 811 — the foot defined as exactly 0.3048 m; NIST — SI units of length; Federal Register, 5 Oct 2020 — the notice deprecating the U.S. survey foot.

Frequently asked questions

How do I convert decimal feet to feet and inches?

Keep the whole number as feet, then multiply everything after the decimal point by 12 to get inches. For 5.75 ft, the 5 stays as feet and 0.75 × 12 = 9, giving 5 ft 9 in. If the inches come out with their own decimal, round that remainder to the nearest fraction your tape measure actually shows.

What is 0.5 feet in inches?

0.5 ft is exactly 6 inches, because 0.5 × 12 = 6. The other clean ones are 0.25 ft = 3 in, 0.75 ft = 9 in, and 0.125 ft = 1.5 in. Anything that is not a simple fraction of 12 will land between the marks on a tape and needs rounding.

Is a tenth of a foot the same as an inch?

No, and assuming it is the single most expensive mistake on a job site. A tenth of a foot is 1.2 inches, so 0.1 ft is 1 3/16 in, not 1 in. The gap widens as the decimal grows: 0.9 ft is 10.8 in, which is nearly 1 3/4 inches away from the 9 in that a careless reading would give.

Why do surveyors and engineers use tenths of a foot instead of inches?

Because decimal feet add, subtract and average with ordinary arithmetic, while feet-and-inches force you to carry in twelfths and then in sixteenths. Survey rods, engineering scales and total stations are graduated in tenths and hundredths of a foot for exactly that reason. The conversion to inches only happens at the point where someone has to cut something.

How do I convert feet and inches back to decimal feet?

Add any fraction to the whole inches, divide the total by 12, and add the feet. For 8 ft 9 3/4 in, that is 9.75 ÷ 12 = 0.8125, giving 8.8125 decimal feet. Use the second tab of the converter above to do it both ways and check your working.

Related tools

• Length converter
• Area converter
• Rule of three calculator
• Percentage calculator
• All tools