What is a length converter?
A length converter translates between different units of distance — meters, kilometers, feet, inches, miles, nautical miles, yards. Different countries and industries use different standards: India + most of the world uses SI metric; the US uses US-customary; aviation and shipping use nautical miles.
This calculator handles every common length unit with high precision, and updates all other units instantly when you change the input.
Supported units
| Unit | Symbol | Equivalent |
|---|---|---|
| Meter | m | Base unit (SI) |
| Kilometer | km | 1,000 m |
| Centimeter | cm | 0.01 m |
| Millimeter | mm | 0.001 m |
| Micrometer (micron) | µm | 10⁻⁶ m |
| Inch | in | 0.0254 m |
| Foot | ft | 0.3048 m |
| Yard | yd | 0.9144 m |
| Mile | mi | 1,609.344 m |
| Nautical mile | nmi | 1,852 m |
How conversion works
target_value = source_value × source_factor / target_factor
where each unit's factor is its value in meters. Internally, every input is converted to meters first, then to the target unit. This avoids cumulative rounding errors when chaining conversions.
Worked example
Convert 5 ft 9 in to centimeters (typical height query):
5 ft = 5 × 30.48 = 152.4 cm
9 in = 9 × 2.54 = 22.86 cm
Total: 152.4 + 22.86 = 175.26 cm
Or directly: 5'9" → 69 inches → 69 × 2.54 = 175.26 cm.
Common conversion shortcuts (mental math)
| Approximation | Use when |
|---|---|
| 1 m ≈ 3.28 ft | Height conversions |
| 1 inch ≈ 2.54 cm | Screen sizes, body measurements |
| 1 km ≈ 0.62 mi | Distances on road maps |
| 1 mile ≈ 1.6 km | US road maps to Indian/EU |
| 1 nautical mile = 1.85 km | Aviation/shipping |
| Body height: 5 ft = 152 cm + each extra inch = 2.54 cm | Quick mental height math |
When precision matters
- Engineering and physics: use full 6+ decimal precision
- Carpentry and construction: 1 mm precision is typical
- Body height / weight forms: 1 cm precision is fine
- Travel / casual: nearest km / mile is enough
Considerations
- "Mil" ≠ millimeter. In US engineering, "mil" = 0.001 inch = 0.0254 mm. Easily confused with millimeter (mm). In jewelry, "mil" sometimes refers to thousandths of an ounce.
- Imperial vs US-customary — they're 99% identical but differ for some volume units (gallon). For length, both use feet/inches consistently.
- Nautical mile is based on 1 minute of arc along a meridian — used for sea/air navigation because it maps to latitude.
Limitations
- The calculator doesn't handle compound inputs like "5 ft 9 in" directly. Convert each part separately or use total inches.
- Floating-point precision shows trailing decimals (e.g. 1.6093440000000001). For real use, take 4-6 decimals.
Related calculators
- Mass / Weight — kg / lb / oz
- Volume — cubic measurements
- Area — square measurements
- Speed — distance / time
- Tire Size — tire-spec to overall diameter
Final note. Unit conversion errors have crashed Mars rovers (the Mars Climate Orbiter was lost in 1999 due to a pound-vs-newton mixup costing $125M). Always confirm which unit system applies before any calculation that matters — pilots verify altitude in feet, scientists in meters, sailors in nautical miles. This calculator removes the guesswork.