Construction Unit Converter

Exact factors, honestly rounded

Every factor on this page traces to two international definitions, of the yard and of the pound: 1 yd = 0.9144 m and 1 lb = 0.45359237 kg, both exact. From those, 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 sq ft = 0.09290304 m², and 1 cu ft = 0.028316846592 m³ follow exactly. The converter multiplies by one whole-number factor and divides by another — nothing else — so 12 ft is exactly 3.6576 m and an 80 lb bag is exactly 36.2873896 kg, shown as 36.2874 kg at 6 significant digits. The methodology page describes the precision contract shared by every tool on this site.

The whole-number design behind that claim — the integer "grain" each unit is counted in, why a product of grains is exact, what a tool's imperial/metric toggle does with the same factors, and why the metric concrete bags carry their own yields — is the subject of the guide Metric and imperial in the estimators. Read it for the mechanism. This page stays with the converter itself: what it does with a number you type, step by step, why each control matters, how to read what comes back, and where it stops.

Where the converter sits in the pipeline

Every estimator on this site runs the five-stage pipeline documented on the methodology page: geometry turns measurements into an area or a volume, coverage divides by what one unit of material covers or yields, waste multiplies by (1 + waste% ÷ 100), package rounding rounds up to whole bags, boxes, or bundles, and user-priced cost multiplies the count by a price you supply. The converter runs none of those five. It performs the step that comes before geometry — the measurement convention that turns whatever your tape or drawing says into the unit the arithmetic wants — and then hands the number back to you. There is no coverage divisor on this page, no waste allowance, no round-up, and no price field: a converted quantity is still a bare quantity, exactly as large as the one you typed and in no way padded for a purchase. When you want the padded figure, the estimator for that material applies its own stages, and its metric toggle performs this same conversion internally before any of them run.

What happens to a number you type

Choose a category, pick a from unit and a to unit inside it, and enter a value. The engine first checks the value: it must be a finite number of zero or more (a quantity of material is never negative; zero is accepted and converts to zero), and it must not exceed 1,000,000,000 in any engine unit — a limit that keeps the product of the value and its grain count inside safe double magnitudes, so nothing overflows, and that sits far beyond construction use. The feet + inches entry and target are the exception: both pass through the geometry engine's feet-and-inches functions, which apply that engine's dimension limit of 1,000,000 ft, so a feet box above it is refused before the grain arithmetic runs, and a result that would exceed it in feet is refused after. The limit is not what makes a conversion exact: a conversion is exact whenever that intermediate product is exactly representable, which the engine records for every value in the printed chart below and which the worked examples claim only where the build checked the result; it is not guaranteed for every value up to the limit. A value that fails the checks is refused with a message rather than converted. If the two units are the same, the value is returned untouched, bit for bit.

Otherwise the conversion is (value × grains of the from-unit) ÷ grains of the to-unit: one multiplication by a whole number, one division by a whole number, and nothing else. The result is held at full precision and formatted only for display — normalised to twelve significant digits to strip binary artefacts, then shown at six. The feet + inches entry adds one step at the front: the inches are divided by 12 and added to the feet, so 5 ft 6 in becomes 5.5 ft before the grain arithmetic runs, and an inches entry of 12 or more is refused so a foot cannot be counted twice. Converting to feet + inches runs the same path in reverse: the engine converts to decimal feet, splits off the whole feet, and multiplies the remainder by 12 without rounding it, so 2.4 m reads as 7 ft 10.4882 in.

Why each control matters

Category is the guard rail. Length, area, volume, and weight are separate lists, and a unit from one can never be paired with a unit from another, which is what keeps the yard on a tape measure apart from the "yard" of concrete: the first is 3 ft of length and the second is a cubic yard, 27 cu ft of volume. Switching category resets both unit menus to a US-to-metric pair — feet to metres, square feet to square metres, cubic yards to cubic metres, pounds to kilograms.

From and to set the two grain counts. The Swap units button exchanges the two units and converts the same entry the other way; it does not carry the result back into the value box, so a round-trip check — converting, swapping, and expecting to land on your entry — needs the result typed into the value box after the swap. Value is the only number that scales the result; everything else on the form is a choice of units. The feet + inches option exists so that a tape reading can be typed as read — 5 and 6 in two boxes — instead of as a decimal you worked out in your head, which is where the decimal-feet misreading described below begins.

The figures this page relies on

This page holds no coverage or yield figure: nothing here is divided by what a bag or a bundle covers. Every unit factor it uses is a definition — the imperial-to-metric ones exact by the international yard-and-pound agreement, the rest definitions within their own system — plus two engine limits, all held once in the site's geometry and converter engines and never re-typed in a page:

• 12 in per ft, 3 ft per yd, 9 sq ft per sq yd, and 27 cu ft per cu yd — definitions within the US customary system.
• 2.54 cm per in, 0.3048 m per ft, 0.09290304 m² per sq ft, and 0.028316846592 m³ per cu ft — the international inch and foot, squared and cubed — and 1,000 L per m³.
• 0.45359237 kg per lb — the international pound; 2,000 lb per US short ton and 1,000 kg per tonne — definitions.
• An upper limit of 1,000,000,000 on any value entered in an engine unit, and of 1,000,000 ft on the feet + inches entry and target — engine limits, not measurements.

Four figures from the site's materials data appear on this page as inputs rather than as factors: the concrete bag weights, one dressed lumber size, the face area of a drywall sheet, and the roofing square. The bag weights in the chart — 40, 50, 60, and 80 lb, the sizes offered in the concrete tools from the QUIKRETE Concrete Mix (Product No. 1101) data sheet, and 25 and 30 kg, the two sizes Target Products publishes for Canada — are packaging labels being converted, not coverage figures; their yields live on the concrete bag calculator. The dressed lumber size used in one example below, 1.5 × 3.5 in for a nominal 2×4, is the minimum dry dressed size from Voluntary Product Standard PS 20-20, Table 3, recorded in the same data module. Two rows of the area chart are also materials-data inputs: 32 sq ft, the face area of a nominal 4 × 8 ft drywall sheet, which the data module labels pure arithmetic on the nominal sheet dimensions and the drywall calculator divides by; and 100 sq ft, the roofing square, an industry definition rather than a measured value, which the roofing shingle calculator counts in. On this page each is simply an area being converted to square metres.

Cubic yards on one side of the ocean, cubic metres on the other

US ready-mix plants sell concrete by the cubic yard — a mixer truck carries several of them — while suppliers in metric countries price and batch by the cubic metre. The two differ by nearly a third: 1.30795 cu yd fit in a cubic metre, and a 5 cu yd order is 3.82277 m³. Bagged material splits the same way: US concrete mix comes in 40, 50, 60, and 80 lb bags, while metric markets sell 25 and 30 kg bags — so a 60 lb bag (27.2155 kg) sits between the two metric sizes and an 80 lb bag (36.2874 kg) is heavier than either, with no US size matching a metric one. Lumber tells the story in length: the 8 ft stud is 2.4384 m, and a 2.4 m length — the metric example worked below — sits close to it but not on it. When a quote crosses systems, convert the quantity first and only then compare prices.

Worked examples

Each figure below was produced when this page was built by the same engine that runs the form, with the inputs chosen to show different behaviours: a quotient that terminates and one that does not, a composite entry, each of the four categories, and metric entries going the other way. Where the text says "exactly", the build checked that the quotient terminated.

A wall line in feet. 12 ft → m: 12 × 0.3048 = 3.6576 m, a terminating product, so the six-digit reading 3.6576 m is the whole answer. The same entry to centimetres is 365.76 cm. The Factor line beneath the headline reads the pair both ways — 1 ft = 0.3048 m and 1 m = 3.28084 ft — and the second of those is the rounded one: 3.28083989501… does not terminate.

A counter height in feet and inches. 5 ft 6 in → m. The inches fold in first: 6 ÷ 12 = 0.5, so the engine converts 5.5 ft and lands on 1.6764 m exactly — 1,676.4 mm on a metric drawing.

A metric length to feet and inches. 2.4 m → ft: 2.4 ÷ 0.3048 = 7.87402 ft, a quotient that does not terminate, so the six digits shown are a rounded reading of a value the engine holds at full precision. With feet + inches as the target the same value reads 7 ft 10.4882 in. Set against the 8 ft stud at 2.4384 m, the two lengths are close, not equal, and the converter shows the gap rather than rounding it away.

A floor in square feet. 1,000 sq ft → m² = 92.90304 m², exactly, because the area factor is the foot factor squared and the product terminates. The same floor in square yards, 111.111 sq yd, does not terminate (1,000 ÷ 9), and the display shows six digits of it. Going the other way, a 60 m² room is 645.835 sq ft.

A ready-mix order in cubic yards. 5 cu yd → m³ = 3.82277428992 m³, exactly: 5 × 27 = 135 cu ft, times the exact cubic-foot factor. The same order in litres is 3,822.77 L. A converted volume is not an order: the allowance and the rounding up to the 0.25 cu yd ordering increment — a trade convention, as the slab engine labels it — belong to the concrete slab calculator, not here.

A metric pour to cubic yards. 2.5 m³ → cu yd = 3.26988 cu yd, rounded (2.5 ÷ 0.764554857984 does not terminate), and 88.2867 cu ft. The litre reading, 2,500 L, is exact, because a litre is a thousandth of a cubic metre by definition and the quotient terminates.

Bags in pounds and kilograms. An 80 lb bag → kg = 36.2873896 kg exactly — 80 × 0.45359237. The two metric sizes go the other way with quotients that do not terminate: 25 kg = 55.1156 lb and 30 kg = 66.1387 lb. Neither lands on a US size, which is why the bag calculator carries a separate yield table for each system rather than converting one into the other.

Tons and tonnes. 3 US short tons → kg = 2,721.55422 kg exactly (3 × 2,000 lb × 0.45359237), or 2.72155422 tonnes. A 10-tonne quantity is 22,046.2 lb and a 10-ton quantity is 20,000 lb — 2,046.23 lb apart, because a tonne is 1.10231 short tons.

A nominal lumber size. Typing the digits of a 2×4 into the converter as inches gives 50.8 × 101.6 mm, which no 2×4 measures. The dressed size from PS 20-20, 1.5 × 3.5 in, converts to 38.1 × 88.9 mm. The converter converts the number it is given; it does not know that a size is a name.

How to read the result

The headline line states the conversion in full — 12 ft = 3.6576 m — with both numbers at six significant digits. Beneath it, the Factor line gives the single-unit factor in both directions, so you can see which way the rounding fell and carry the factor to a calculator of your own. The Exact line quotes the definition behind the imperial unit involved — 1 ft = 0.3048 m exactly, 1 lb = 0.45359237 kg exactly, and so on — with the reminder that only the display is rounded. The line quotes only the definitions the engine records, so a conversion between two metric units shows one only where a metric unit carries its own, as the litre does as a thousandth of a cubic metre. When feet + inches is the target, the inches are shown at six significant digits, and a float artefact that would display as twelve inches is carried into the feet, so the reading can never show an impossible inch count. The Copy result button places the headline on the clipboard as shown — six significant digits — so a copied value carries display rounding. For a figure that will feed an estimate, type the original measurement into that estimator's metric fields instead; the conversion then happens inside the tool at full precision.

Common misreadings

Inches entered as feet. The house example across this site is a thickness typed in the wrong unit, and the converter has the same trap on its first menu. Enter 12 with feet selected and the result is 3.6576 m; enter the same 12 meaning inches and the correct answer is 0.3048 m — a factor of 12. The converter cannot tell which you meant, because the arithmetic is right either way; read the From menu before you read the result. The slab calculator's thickness box shows what the same slip does to a concrete order.

Millimetres and centimetres. The metric version is a factor of 10: 25 cm is 9.84252 in, while 25 mm is 0.984252 in. A figure read in millimetres and typed as centimetres, or the reverse, is the metric form of the same slip, and the Exact line will not catch it, because both entries are valid.

Decimal feet that are really feet and inches. 12.6 ft is not 12 ft 6 in. The engine reads the decimal as a fraction of a foot, and with feet + inches as the target it shows 12.6 ft as 12 ft 7.2 in — 30.48 mm longer than the 12 ft 6 in intended, which is 12.5 ft and 3.81 m against 3.84048 m. Use the feet + inches option, or divide the inches by 12 before typing. Fractions of an inch go through the feet & inches calculator, which works in sixteenths; this converter takes decimal inches.

A yard that is a cubic yard. Trade shorthand drops the "cubic", and a length conversion of a concrete quantity means nothing. The category menu prevents the pairing, but it cannot prevent the wrong category being chosen: a "yard" of concrete, gravel, or mulch belongs under Volume, where it is 27 cu ft and 0.764554857984 m³, not under Length.

A ton that is a tonne. Both are offered under Weight, and they differ by 10.2311%. A quantity converted with the wrong one is wrong by that margin in whichever direction the mix-up ran, which is why the chart lists both and the Exact line names the one in use.

Six digits read as the exact value. 2.4 m shows as 7.87402 ft, but the engine's value continues past the sixth digit, and a reading copied from the screen and multiplied back by hand will not return to 2.4 exactly. A terminating result such as 3.6576 m is complete as displayed; a rounded one is not, and the guide linked above explains how to tell the two apart.

Where the converter stops

Conversions are unit arithmetic on the numbers you enter. The converter cannot correct a mismeasured dimension, a misread drawing, or a wrong unit selection, and it does not know what the number describes. It converts within a category only: there is no path from weight to volume, because that needs a material density — the gravel calculator takes a density as your input for exactly this reason — and no path from a length to an area, which is geometry, not conversion. It covers four categories and no more: no temperatures, pressures, or rates, and no board feet, which have their own calculator. It takes decimal inches, not tape fractions. It does not translate packaging, ordering increments, delivery minimums, or product sizes between systems; it carries no coverage or yield figure; it applies no waste and rounds nothing up. And the site-wide boundary applies here as everywhere: these are quantities and units only, never structural adequacy, code compliance, or engineering suitability, which belong to a licensed engineer, architect, or code official.

The estimators already speak both systems

Every estimator that offers metric entry has an imperial/metric toggle that uses these same exact factors, so you rarely need to convert by hand before estimating. Measure in whichever system your tape uses and go straight to the square footage, volume, linear feet, feet & inches, stair, roof pitch, board foot, concrete slab, concrete bag, brick, concrete block, concrete footing, concrete column, post hole concrete, rebar, paver, gravel, topsoil, mulch, sand, sod, paint, drywall, flooring, tile, wallpaper, insulation, roofing shingle, siding, fence, or deck material calculator — this page is for the moments in between: reading a metric drawing with an imperial tape, comparing a tonne price to a ton price, or translating a materials list for a supplier in the other system.

Frequently asked questions

Related: the guide Metric and imperial in the estimators for the grain design and the unit toggles, the feet, inches, and fractions guide for the tape-measure side, the Feet & Inches Calculator for sixteenths, the Concrete Bag Calculator for both bag tables, and the full list of guides.

Nothing you type leaves your device. These are unit conversions and quantity estimates only — no structural adequacy, code compliance, or engineering judgment; verify dimensions and local code with a professional. See how every tool is built and tested on the methodology page.