Millimeters to Feet Converter, mm ⇄ ft, in, cm, m

The millimetre is the workhorse unit of precision engineering: CNC toolpaths are written in mm, 3D-printer slicers speak mm, engineering drawings almost everywhere outside the United States are dimensioned in mm, and the millimetre is the unit on every metric tape measure, calliper, and micrometer on the planet. The foot, meanwhile, is still the everyday unit in US construction, US aviation altitude, US lumber sizing, US real-estate floor plans, and a few niche trades worldwide. Converting between them is one of the most common jobs in any workshop that straddles the metric/imperial line.

This converter gives you an exact, bidirectional mm ↔ ft calculation together with the four related read-outs you almost always want alongside it, inches, centimetres, metres, and the carpentry-style "feet & inches" form (e.g. 6 ft 2.4 in). The math is anchored to the 1959 international yard and pound agreement: 1 ft = 0.3048 m exactly, which means 1 ft = 304.8 mm exactly, with no rounding ambiguity.

How to Use

1. Pick the field that matches the number you already have. If your drawing says 1524 mm, click into the Millimetres box. If your plan says 5 ft, click into Feet.
2. Type the number. You can use decimals (1828.8, 1.75) and you can paste in a value with thousand-separators or trailing zeros, the input accepts any valid decimal.
3. Watch the other field update as you type. Conversions happen live with every keystroke; you don't need to press Enter.
4. Read the bonus rows. The result panel below the inputs shows the same length expressed in inches, centimetres, metres, and split as X ft Y.YY in, the way a carpenter would write it on a cut-list.
5. Use the swap button (⇄) when you only have one number. Type it in either field, hit swap, and the other side now holds the converted value, ready to copy.
6. Copy the answer you need. Each copy button grabs exactly the value and unit you see on screen, including the thousand-separators on the mm field, so you can paste straight into a BOM, a G-code comment, or an email.
7. Verify with a known anchor. The footer always shows 1 ft = 304.8 mm exactly, so you can sanity-check that the conversion is using the international foot (and not the legacy US Survey foot, which is about 2 ppm larger).
8. For decimal feet, remember there are 12 inches in 1 ft. A length of 0.25 ft is 3 in exactly, and the "feet & inches" row will show 0 ft 3.0000 in.

The Formulas

All the conversions on this page rest on one exact relationship:

1 ft = 0.3048 m exactly (1959 international yard, ratified by the US, UK, Canada, Australia, New Zealand, South Africa)

Since 1 m = 1000 mm exactly (SI definition, 1960), we can derive the foot↔millimetre conversion with zero ambiguity:

• 1 ft = 0.3048 m × 1000 mm/m = 304.8 mm exactly
• 1 mm = 1/304.8 ft = 0.00328083989501... ft

From there the rest falls out for free:

• 1 in = 25.4 mm exactly (NIST, 1959), so 1 mm = 1/25.4 in = 0.03937007874015... in
• 1 ft = 12 in exactly (US customary)
• 1 cm = 10 mm exactly (SI)
• 1 m = 1000 mm exactly (SI)

Forward conversion (mm → ft):

feet = millimetres × (1 ft / 304.8 mm) = millimetres × 0.00328083989501...

Reverse conversion (ft → mm):

millimetres = feet × (304.8 mm / 1 ft) = feet × 304.8

Inches from millimetres:

inches = millimetres × (1 in / 25.4 mm) = millimetres × 0.03937007874015...

Feet & inches from millimetres (the form carpenters use):

total_inches = millimetres / 25.4
feet = floor(total_inches / 12)
inches = total_inches − feet × 12

Worked Examples

1. A 6-foot-tall person, in millimetres

The US median adult male height is about 5 ft 9 in (1.75 m). A 6 ft person is 6 × 304.8 = 1828.8 mm, exactly, no rounding. This is the kind of conversion that shows up when sizing door frames, ergonomic furniture, cabin headroom, and theatrical set pieces for an international audience. Enter 1828.8 mm in the mm field and you'll read back exactly 6.00000000 ft, with the feet-and-inches row showing 6 ft 0.0000 in.

2. A 100 mm board, in feet

A standard offcut from a European workshop might be 100 mm long. Dividing by 304.8 gives 0.32808398950... ft. Multiplying back, that is 3.93700787401... in. So if you're reading an imperial plan and the callout says "0.328 ft", you know you're looking at a metric part dimensioned in mm but printed on a US sheet. Enter 100 mm and the converter shows 0.32808399 ft and 3.93700787 in.

3. A 1.75 mm guitar string gauge

Electric guitar high-E strings are commonly 1.75 mm in diameter, about 0.0057414698 ft, or 0.0688976378 in. This is a nice example of where the foot conversion is essentially useless in practice (nobody thinks in feet for a guitar string) but the inch read-out is exactly what a parts list asks for: 0.0689 in is meaningful to a luthier or pickup winder. Use the inch row, ignore the foot row.

4. A 10 ft length of 2×4

US lumber is sold in nominal foot lengths. A 10 ft 2×4 is 10 × 304.8 = 3048 mm exactly, which lines up neatly with the 3 m metric length that European lumber yards stock, the difference between 3048 mm and 3000 mm is the 48 mm the lumber industry quietly absorbs into the "actual" size vs. the nominal size. Enter 10 ft and the converter shows 3048.0000 mm, 3.0480 m, 120.000000 in, and 10 ft 0.0000 in.

5. A 1524 mm workbench top

Many UK/AU workbench plans are dimensioned in mm even when the author thinks in feet. A 1524 mm (5 ft) bench top is the canonical size because it works out to a clean 5.00000000 ft. This is also exactly 60 in, which is the imperial equivalent and a useful sanity check for imperial-tool owners. Enter 1524 mm and you'll see 5.00000000 ft, 60.000000 in, and the carpentry-style 5 ft 0.0000 in.

Where It Shows Up

• CNC machining. Every GRBL, Mach3, Haas, and LinuxCNC post-processor speaks mm. When you load a US customer's .dxf or .step file with dimensions in inches, you typically rescale to mm before machining, this converter is the inverse of that step, useful when a metric CAM file is being reviewed by an imperial shop.
• 3D printing. Slicers (PrusaSlicer, Cura, OrcaSlicer) default to mm, but most Thingiverse/Bambu/Printables model descriptions still quote dimensions in inches for US audiences. A quick mm→ft check tells you whether a print will fit on a US-spec shelf, a US-spec picture rail, or a US-spec printer bed quoted in inches.
• Engineering drawings. ISO drawings are mm-only. ASME Y14.5 (US) drawings are inches-first. Multinational OEMs increasingly dimension both, and the conversion must be exact, not "close enough".
• Architecture and construction. US floor plans use feet-and-inches (14'-6"). International plans use mm. Converting between the two without losing a 1/8" tolerance is a daily task for any firm working across the US/EU/UK border.
• Screen sizes. Monitor and TV diagonals are universally quoted in inches (a 27" monitor is a 685.8 mm diagonal), while projector throw distances and screen widths are commonly given in mm in spec sheets. The converter goes both ways cleanly.
• Rainfall and snow measurement. US weather stations and the NWS report precipitation in inches; the WMO standard (and every other national met service) reports it in millimetres. Converting back and forth is routine for cross-border climate studies, ski-resort marketing copy, and agricultural planning.
• Surveying and GIS. Elevation is metres globally; US legacy contour maps are feet. The international foot (304.8 mm) is the right conversion, the older US Survey foot (304.8006 mm) only matters for historical NGS benchmarks, which is why this converter sticks to the international foot.
• Sports. Basketball rims are 10 ft (3048 mm) high; climbing grades often quote holds in mm while route descriptions quote heights in ft; sailing rigging is feet-of-line for US sailors and metres for everyone else.

Common Mistakes

1. Confusing millimetres with centimetres. This is the single most common error. A 25.4 mm part is 1 inch, not 2.54 inch. If you mentally swap mm and cm you'll be off by a factor of 10, a 25.4 mm shaft will become a 254 mm (10 in) phantom monster in your BOM. Always read the unit, twice.
2. Forgetting the thousand-multiplication. 1 m = 1000 mm, not 100 mm. A lot of students and new engineers instinctively think of a metre as "a bit more than a yard" (~914 mm) and try to use ~900 mm as the conversion. It's exactly 1000. Three zeros. The converter's Also in metres row is the easiest way to catch this: if you typed 1524 mm and the metres row says 15.240 instead of 1.524, you forgot a factor of 10 somewhere.
3. Using the US Survey foot by accident. The US Survey foot is 1200/3937 m = 0.3048006096... m, about 2 parts per million larger than the international foot. The difference is invisible on a single workpiece but accumulates over miles of surveying, and over a 50 ft timber-frame span it's already a 0.03 mm error, which matters in precision timber work. Stick to the international foot (304.8 mm exactly) unless you are explicitly working with US geodetic survey data from before the 1959 redefinition.
4. Rounding the foot to 300 mm. A lot of pocket calculators and older reference tables used 1 ft ≈ 300 mm or 1 ft ≈ 305 mm for "quick" conversions. Over a 10 ft length that error is 48 mm, almost 2 inches, and enough to scrap a part. The exact value is 304.8 mm, and this converter uses it. If your mental shortcut disagrees with the converter, trust the converter.

Frequently Asked Questions

How many millimetres are in a foot, exactly? Exactly 304.8 mm, with no rounding. This comes from 1 ft = 0.3048 m (the 1959 international yard) and 1 m = 1000 mm (the SI definition). The conversion is exact because both anchor constants are exact. The reverse is 1 mm = 1/304.8 ft ≈ 0.00328084 ft.

How do I convert feet and inches to millimetres? Take the whole feet, multiply by 304.8, then add the inches × 25.4. For a length like 6 ft 2 in: 6 × 304.8 + 2 × 25.4 = 1828.8 + 50.8 = 1879.6 mm. Or use this converter's "As feet & inches" row in reverse, type the total mm and read off the split.

How many mm are in an inch? Exactly 25.4 mm (NIST). One inch equals 25.4 mm exactly, and one foot (12 inches) equals 304.8 mm exactly.

Is a foot the same length in the US and the UK? Yes, since 1959. The US, UK, Canada, Australia, New Zealand, and South Africa all adopted the international yard of exactly 0.9144 m, which gives exactly 0.3048 m (304.8 mm) per foot. The only surviving exception is the US Survey foot, which is 1200/3937 m ≈ 304.8006 mm and is only used in legacy US geodetic surveys.

Why do engineers prefer millimetres over centimetres? Two reasons. First, the millimetre is the natural unit for precision work, a 0.05 mm tolerance is a 0.05 mm tolerance, but a 0.005 cm tolerance reads awkwardly. Second, the millimetre is the SI base-1000 subdivision of the metre, so dimensional analysis stays clean without the decimal-place confusion that centimetres introduce.

What is 5 ft 8 in in millimetres? 5 × 304.8 + 8 × 25.4 = 1524 + 203.2 = 1727.2 mm. Type 1727.2 into the mm field and the "feet & inches" row will show 5 ft 8.0000 in as a round-trip check.

What is 100 mm in feet and inches? 100 / 25.4 = 3.93700787 in. That is 0 ft 3.9370 in, or about a quarter of a foot (0.3281 ft). Useful when checking whether a metric part fits a US-spec cutout.

What is 1000 mm in feet? 1000 / 304.8 = 3.28083989501 ft, i.e. roughly 3 ft 3.37 in. This is one of the most-typed conversions on the web.

Is this converter accurate enough for engineering use? Yes, it uses exact decimal arithmetic anchored to the 1959 international yard. For lengths up to a few kilometres the IEEE-754 double-precision arithmetic used here is good to better than 1 part in 10¹², far below the tolerance of any physical measurement you can make with a tape, a calliper, or a laser interferometer. For sub-micron work you would want arbitrary-precision arithmetic, but that is well outside the scope of a workshop converter.

References

• NIST Special Publication 811, Guide for the Use of the SI, for the exact millimetre-foot relationship (1 ft = 0.3048 m). https://www.nist.gov/pml/special-publication-811
• ISO 80000-1:2022, Quantities and Units, for the unit symbols used. https://www.iso.org/standard/76921.html