Length Converter

Convert between millimeters, meters, inches, feet, and many more length units.

Supports 27 length units across metric, imperial, and astronomical systems.

Updated August 1, 2026

CreatorFrank Zhao

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Introduction / overview

The Length Converter translates any length you type into a whole row of other units at once — millimeters, centimeters, meters, kilometers, inches, feet, yards, miles, nautical miles, and even cosmic scales like light years and parsecs.

It’s a two-way street: type a value into any box and every other unit updates instantly. No need to figure out which direction to convert.

Who is this for?

Travelers comparing road distances, flights, or luggage rules across metric and imperial countries.
DIYers and woodworkers juggling feet-and-inches with metric measurements.
Engineers, students, and hobbyists who want one reliable place for any unit — including astronomy.

Because the conversion runs through the meter using exact definitions — the international foot is exactly $0.3048\ \mathrm{m}$ , a nautical mile exactly $1852\ \mathrm{m}$ , and the astronomical unit exactly $149\,597\,870\,700\ \mathrm{m}$ — the results are reliable and repeatable. If you only ever need feet and inches, our Feet to Inches Calculator is the more focused tool; this one is for when you want the whole picture.

How to use / quick start

1Type a length into whichever box is most natural — meters, feet, miles, it doesn’t matter. The rest of the fields fill in on their own.
2Want a unit that isn’t on its own row? The “other metric units”, “other imperial units”, and “other units” fields each hold a menu of extra choices — from picometers to parsecs, mils to megaparsecs.
3For compound measurements, switch to meters / centimeters or feet / inches so you can enter something like 5 ft 6 in in two boxes.
4Edit a different field to convert the other way — the converter is fully bidirectional, so whatever you type becomes the source and everything else re-derives from it.

Worked example — a person is 5 ft 6 in tall. What is that in meters and centimeters?

5\ \mathrm{ft}

=

5 \times 0.3048\ \mathrm{m}

=

1.524\ \mathrm{m}

6\ \mathrm{in}

=

6 \times 0.0254\ \mathrm{m}

=

0.1524\ \mathrm{m}

1.524 + 0.1524

=

1.6764\ \mathrm{m}

=

167.64\ \mathrm{cm}

In the calculator, just pick feet / inches on the imperial field, type $5$ and $6$ , and read 1.6764 m alongside every other unit.

Worked example — a 1-mile commute expressed in kilometers

1\ \mathrm{mi}

=

1609.344\ \mathrm{m}

=

1.609344\ \mathrm{km}

Type $1$ into “Length in miles” and the kilometers box shows 1.609344 km — handy when renting a car abroad.

How to read the results

The number you typed stays black; the auto-calculated values appear in blue so you always know which one you entered.
Long repeating results are rounded for easy reading (for example $1\ \mathrm{m} \approx 3.28084\ \mathrm{ft}$ ), while the conversion keeps full accuracy.

Real-world examples

Planning a race distance in miles

You signed up for a 5 km fun run, but your watch and most US running routes think in miles. Type $5$ into the kilometers box:

5\ \mathrm{km}

=

5000\ \mathrm{m}

\frac{5000}{1609.344}

\approx

3.107\ \mathrm{mi}

So 5 km is about 3.1 miles — the distance most beginners can finish comfortably. Knowing this helps you pace a training route around a familiar loop.

Reading a European hardware spec

An IKEA-style bracket says the drill spacing is 12 cm, but your tape measure is marked in inches. Convert $12\ \mathrm{cm}$ :

12\ \mathrm{cm}

=

0.12\ \mathrm{m}

\frac{0.12}{0.0254}

\approx

4.72\ \mathrm{in}

Mark 4.72 inches, or about $4\frac{3}{4}$ inches on your rule. If you need an exact fractional cut, our Inches to Fraction Calculator turns decimal inches into eighths and sixteenths for you.

Earth to Sun, in everyday units

The average Earth–Sun distance is exactly one astronomical unit. Pick au in the “other units” field and type $1$ :

1\ \mathrm{au}

=

149\,597\,870\,700\ \mathrm{m}

\frac{149\,597\,870\,700}{1000}

\approx

149.6\ \mathrm{million\ km}

That’s about 8.3 light-minutes — a fun sanity check whenever you see astronomy news quoting “one AU” and want it in kilometers.

Planning a sailing leg in nautical miles

Your chart marks a passage of 10 nautical miles. Type $10$ into the nautical-miles box and read the kilometers:

10\ \mathrm{nmi}

=

10 \times 1852

=

18\,520\ \mathrm{m}

=

18.52\ \mathrm{km}

Handy for comparing chart distances with the land-based kilometer signs on coastal roads.

Common scenarios / when to use

Travel & navigation

Renting a car, reading speed limits, or comparing hikes across countries that use different unit systems. Especially useful when you mix kilometers, miles, and nautical miles. Pair it with our Temperature Converter to handle the °C/°F switch while you’re at it.

DIY & home improvement

Board lengths, furniture clearances, and room dimensions that come in mixed units. The feet / inches and meters / centimeters fields keep compound measurements in one place instead of two separate conversions.

Fitness & sports

Translating race distances (5 km vs 3.1 miles), track lengths, or stride measurements. Quick and handy when your device reports in one system and your training plan uses another.

Science & astronomy

When numbers get huge, switch to astronomical units, light years, parsecs, or Sun radii instead of juggling millions of zeros in meters or kilometers.

When it’s less useful

For precision land surveying, the tiny difference between the international foot and the US survey foot can matter over long distances. The converter includes the survey foot for reference, but for legal or boundary work you should confirm which standard your jurisdiction requires with the responsible authority.

Tips & best practices

Type in the unit you know

Don’t convert twice. If your source is in feet, type into the feet box and let everything else follow. Fewer manual steps means fewer places to make a mistake.

Keep compound units together

Use “feet / inches” or “meters / centimeters” for measurements like height so the two parts stay as one value instead of being rounded separately.

Watch the “mile” vs “nautical mile” trap

A statute mile is 1,609.344 m; a nautical mile is 1,852 m — about 15% longer. Aviation and marine charts use nautical miles, so check which one you’re actually looking at.

Use big units for big distances

For astronomy, prefer au, light years, or parsecs over meters — otherwise you’ll be staring at twenty-plus digits and losing track of what they mean.

Getting the most accurate result

Enter as many digits as you have. The conversion itself is exact for defined units, so the result is only as precise as your input.
Keep everything in one unit system for a project. Mixing feet for one dimension and meters for another is the most common source of confusion.
When comparing products from different countries, convert both to a common unit (usually meters) before judging sizes.

Calculation method / formula explanation

Every unit is defined by how many meters it equals. The converter first turns your number into meters, then into the target unit — so any two units can talk to each other without a separate formula for each pair.

The general conversion

L_t = L_s \times \frac{f_s}{f_t}

where $L_s$ is the value in the source unit, $L_t$ is the value in the target unit, $f_s$ is meters per source unit, and $f_t$ is meters per target unit.

Converting a mile to kilometers, step by step

L_m

=

1 \times 1609.344

=

1609.344\ \mathrm{m}

L_t

=

\frac{1609.344}{1000}

=

1.609344\ \mathrm{km}

Exact definitions behind the units

Unit	Exact value in meters
inch (international)	0.0254
foot (international)	0.3048
yard	0.9144
mile	1609.344
nautical mile	1852
astronomical unit (au)	149,597,870,700
light year (ly)	9,460,730,472,580,800
US survey foot	1200 / 3937

A few definitions worth seeing

1\ \mathrm{ly}

=

365.25 \times 86\,400 \times c

1\ \mathrm{pc}

=

\frac{648\,000}{\pi}\ \mathrm{au}

1\ \mathrm{sft}

=

\frac{1200}{3937}\ \mathrm{m}

The light year uses the Julian year and the exact speed of light $c = 299\,792\,458\ \mathrm{m/s}$ . The parsec is defined by geometry — the distance at which one astronomical unit subtends one arcsecond. Sun and Earth radii use the standard IAU nominal values (695,700 km and 6,371 km).

Variable guide

$L_s$ — numeric length in the source unit
$L_t$ — numeric length in the target unit
$f_s$ — meters per source unit
$f_t$ — meters per target unit

Related concepts / background info

Why the meter is the anchor

The meter is now defined by the speed of light — exactly the distance light travels in a vacuum in $\frac{1}{299\,792\,458}$ of a second. Because it’s absolute, every other length unit can be pinned to it precisely, which is why the converter can treat them all as clean multiples of a meter.

International foot vs. US survey foot

The international foot is exactly $0.3048\ \mathrm{m}$ . The US survey foot is exactly $\frac{1200}{3937}\ \mathrm{m}$ — about $0.6\ \mu\mathrm{m}$ longer. For everyday measuring the difference is invisible, but across hundreds of thousands of feet (mapping, state plane systems) it adds up. NIST has largely deprecated the survey foot in favor of the international foot.

The nautical mile is built for maps

One nautical mile equals exactly $1852\ \mathrm{m}$ , chosen to match one minute of latitude. That’s why sailors and pilots use it — it lines up neatly with coordinates, while a statute mile doesn’t.

Astronomical units make the cosmos readable

Inside the Solar System we use astronomical units; to stars, light years; across galaxies, parsecs (or megaparsecs). Each is just a practical bucket for a different magnitude of distance, which is exactly why the converter offers all of them.

Go further: once you’ve got lengths sorted, our Area Converter handles square feet, acres, and hectares — perfect for land and flooring. And if you’re measuring a person’s height in feet and inches, the Height in Inches Calculator converts it straight to a single inches figure.

Frequently asked questions

How do I convert meters to feet?

Type the value into “Length in meters” and read the feet box — it updates automatically. To do it by hand: $\mathrm{ft} = \frac{\mathrm{m}}{0.3048}$ . For example, $2\ \mathrm{m} \approx 6.56\ \mathrm{ft}$ .

How many meters are in a mile?

Exactly $1609.344\ \mathrm{m}$ , so a mile is about $1.609\ \mathrm{km}$ . If you see “mile” on a marine chart or a flight plan, check whether it actually means a nautical mile ( $1852\ \mathrm{m}$ ).

What’s the difference between a mile and a nautical mile?

A statute mile is $1609.344\ \mathrm{m}$ ; a nautical mile is $1852\ \mathrm{m}$ — about 15% longer and tied to one minute of latitude. Air and sea navigation use nautical miles; roads and sport use statute miles.

Can I convert light years to kilometers?

Yes. Pick ly in the “other units” field, type the number, and read the kilometers — or better, switch that same field to au or parsecs for a more sensible scale. One light year is $9.46 \times 10^{15}\ \mathrm{m}$ , so the km figure runs into the trillions.

How do I enter “5 feet 6 inches”?

Switch an imperial field to feet / inches, then type $5$ into the feet part and $6$ into the inches part. The metric row updates to 1.6764 m, and the meters / centimeters field offers the reverse for compound metric input.

Why does a result show only a few decimal places?

Conversions like $1\ \mathrm{m} \to 3.280839895\ldots\ \mathrm{ft}$ go on forever. The display rounds to a practical number of digits so the page stays readable, while the conversion keeps full precision internally — your typed value is never rounded down or shortened.

What is the US survey foot, and do I need it?

It’s a slightly longer foot ( $\frac{1200}{3937}\ \mathrm{m}$ ) once used in US surveying. It differs from the international foot by only about half a micrometer, but that compounds over long distances. Unless you’re doing legacy survey work, use the international foot; NIST has largely retired the survey version.

Can I enter a negative length?

Length is a distance, so negative values don’t make physical sense. If you type one, the calculator flags it with a friendly message instead of showing a meaningless negative result. Clear the box and re-enter a positive number.

Limitations / disclaimers

This is a unit conversion tool — the math is exact for the defined units it uses. A few practical boundaries are worth knowing:

•Some values are nominal standards, not physical measurements — Sun radius (695,700 km) and Earth radius (6,371 km) are IAU reference values, and the light year / parsec use the IAU definitions. They’re the right values for astronomy, but they’re definitions you should know you’re using.
•The US survey foot is included for reference, but NIST has deprecated it for most uses; for legal or boundary surveying, confirm the required standard with the local authority.
•Results are only as precise as the numbers you enter. The converter keeps your full value, but the visible display rounds long decimals for readability.

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