glunty Length converter (metric + imperial)
Type a value in mm, cm, m, km, inches, feet, yards, or miles. The rest update live. Local only.
- Runs in your browser
- No sign-up
- No watermark
- No installs
What this tool does
Converts a length or distance between the eight units people use most: millimeters,
centimeters, meters, and kilometers on the metric side, plus inches, feet, yards, and
miles on the imperial side. It is two-way and live, so typing a valid number in any
field updates the other seven instantly, with no button to press and no direction to
choose. Every value passes through one canonical base, the meter, using exact factors:
1 in = 0.0254 m, 1 ft = 0.3048 m, 1 yd = 0.9144 m,
and 1 mi = 1609.344 m. Everything runs in your browser with plain
JavaScript; nothing you type leaves your machine. Verify it yourself: open DevTools,
open the Network tab, and watch it stay empty. Zero requests.
How to use it
Put your number in the field for the unit you already have. To convert centimeters to
inches, type into the Centimeters box and read the Inches box. To convert feet to
meters, type into the Feet box and read the Meters box. Any field can be the source;
the other seven recompute from it. Results are trimmed to at most ten significant
digits with trailing zeros removed, so 30.48 shows cleanly and exact
conversions stay exact. Non-numeric input shows a short inline message and leaves the
other fields untouched, and clearing a field empties the rest so no stale value
lingers. Press Clear to reset every field. Two quick sanity checks:
1 foot reads 12 inches and 30.48 centimeters, and 1 meter reads 100 centimeters.
Common use cases
- Converting a height or room measurement between metric and imperial for a project or listing.
- Reading an overseas spec sheet in the units you actually think in.
- Turning a running or cycling distance from miles into kilometers, or back.
- Checking fabric, lumber, or hardware dimensions given in inches against a metric ruler.
- Sizing print or screen layouts where inches and millimeters both appear.
Common pitfalls
- Feet and inches are separate units here. A height written as 5 feet 9 inches is not 5.9 feet. Convert the inches part on its own (9 inches), or enter the whole height in inches (69), to get a correct metric value.
- A mile is not exactly 1600 meters. The exact factor is 1609.344 meters, so rounding it to 1600 shifts a marathon by more than 200 meters. This tool always uses the exact value.
- Rounding is for display only. Output is trimmed to ten significant digits, which is plenty for any everyday length, but do not read the shown digits as unlimited precision.
- Metric prefixes are powers of ten, not of twelve or three. 1 meter is 100 centimeters and 1000 millimeters; only the imperial side uses 12 (inches per foot) and 3 (feet per yard).
Frequently asked questions
- How do I convert centimeters to inches?
- Type your value into the Centimeters field and read the Inches field. There are 2.54 centimeters in one inch, so the tool divides by 2.54: 10 cm is about 3.937 inches, and 30 cm is about 11.811 inches. It works both ways, so typing into the Inches field fills Centimeters using 1 inch = 2.54 cm. Every field stays in sync as you type.
- How do I convert feet to meters?
- Type your value into the Feet field and read the Meters field. One foot is exactly 0.3048 meters, so 6 feet is 1.8288 meters and 10 feet is 3.048 meters. Type into the Meters field to go the other way, where 1 meter is about 3.28084 feet. All eight fields recompute from whichever one you edit.
- What exact conversion factors does this tool use?
- It uses the internationally agreed definitions: 1 inch = 0.0254 meters, 1 foot = 0.3048 meters, 1 yard = 0.9144 meters, and 1 mile = 1609.344 meters. The metric units are simple powers of ten of the meter: 1 kilometer = 1000 meters, 1 meter = 100 centimeters = 1000 millimeters. Because these factors are exact, round-number conversions like 1 foot = 30.48 cm come out clean.
- How does the converter round its results?
- Each result is rounded to at most ten significant digits, then trailing zeros are trimmed, so an exact value like 30.48 stays 30.48 rather than showing a long floating-point tail. Ten significant digits is far more than everyday use needs and still avoids visual noise. The field you are typing in is never rewritten, so your own input is left exactly as entered.
- Can it handle very large or very small distances?
- Yes. Enter a marathon as 42195 meters, or a hair width as 0.05 millimeters, and every other field updates. Very small results, such as a millimeter expressed in miles, are shown in plain decimal form rather than scientific notation. The math uses standard JavaScript numbers, which carry about fifteen digits of precision, plenty for any real-world length.
- Does the converter send my numbers anywhere?
- No. Every conversion runs in your browser using plain JavaScript arithmetic. Nothing you type is uploaded, logged, or sent to a server. You can verify it: open DevTools, watch the Network tab, and it stays empty while you use the tool. Zero requests.
Cite this tool
For academic, journalistic, or technical references. Pick a format:
Citations use 2026 as the publication year. Access date is left as a fillable placeholder where the citation style expects one.