📏 Length Converter
Convert m, cm, mm, km, in, ft, yd, mi. Runs privately in your browser.
Exact factors, fixed by international agreement
The converter uses internationally defined exact factors: 1 inch = 25.4 mm exactly, 1 foot = 0.3048 m exactly, 1 mile = 1609.344 m. Because every unit is defined against the metre, conversions chain cleanly through a single base — the calculator converts your input to metres, then to the target unit.
That chain matters for precision. Chaining rounded steps (ft → in → cm, each rounded) can drift by fractions you then multiply into errors. This tool keeps full precision internally and trims only the display.Beyond the base units, real conversions usually involve compound expressions — feet and inches together, or metres plus centimetres. The practical pattern: convert each component separately and add. A person listed at 5 ft 9 in is 5 × 0.3048 + 9 × 0.0254 = 1.7526 m. Height charts, door frames and TV diagonals all live in this mixed-unit territory, which is why the calculator keeps every factor exact instead of approximating.
Converting through the metre
value_in_target = value × (factor_from ÷ factor_to), where every factor is defined exactly against the metre: cm 0.01, mm 0.001, km 1000, in 0.0254, ft 0.3048, yd 0.9144, mi 1609.344.
Imperial pitfalls
- Confusing US customary and old imperial feet — for everyday purposes they're identical (both 0.3048 m), but historical 'feet' differ.
- Rounding too early in chained conversions, as with sheet-metal or 3D-printing dimensions.
- Forgetting that nautical miles (1852 m) are a different unit from statute miles.
- Typing comma decimals into a period-locale input — enter 5.5, not 5,5.Converting screen diagonals assuming a 16:9 ratio without checking — many monitors and laptops are 16:10 or 3:2, so the same diagonal yields different width and height.
A marathon and a six-foot person
A 26.2-mile marathon: 26.2 × 1609.344 = 42,164.8 m ≈ 42.2 km. A 6-foot person: 6 × 0.3048 = 1.8288 m ≈ 183 cm. A 10 km run is 10,000 ÷ 1609.344 = 6.21 miles.
Length questions
How many feet in a metre?
Exactly 3.280839895 ft — enter 1 m to see it. The factor 0.3048 m/ft is exact by international definition.
Is 1 mile exactly 1.6 km?
No — it's 1.609344 km. The 1.6 shortcut is fine for estimates, wrong for engineering.
Are inches still defined physically?
Since 1959 the inch has been defined as exactly 25.4 mm; no physical yard artifact is involved.
Can I convert feet-and-inches expressions like 5'9"?
Convert feet and inches as separate steps (5 ft + 9 in), or enter 5.75 ft — the tool takes decimal feet.
Why does the result show many decimals?
The tool preserves precision and lets you round. Rounding inside the calculation would compound errors across conversions.
What is a kilometer in miles?
1 ÷ 1609.344 = 0.62137 mi. The marathon is 26.2 mi ≈ 42.16 km.
How tall is 6 feet in cm?
6 × 0.3048 = 1.8288 m = 182.88 cm — enter 6 ft and read the cm result.
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Tip: double-check inputs before relying on results for important decisions.