Length Converter
3.2808399 ft
- 1,000,000,000
- nm
- 1,000,000
- µm
- 1,000
- mm
- 100
- cm
- 1
- m
- 0.001
- km
- 39.3701
- in
- 3.28084
- ft
The length converter handles 12 units from nanometres to light years, showing the eight most common conversions at once rather than one at a time. Imperial values are exact, not approximate: since the 1959 international yard and pound agreement, one inch is defined as precisely 25.4 millimetres.
How it works
result = value x (factor of source unit) / (factor of target unit)
- factor
- how many metres one of that unit equals. The metre is the base for every length here
- Metric: nanometre, micrometre, millimetre, centimetre, metre, kilometre.
- Imperial and US customary: inch (exactly 0.0254 m), foot, yard, mile.
- Marine and astronomical: nautical mile (exactly 1,852 m by international agreement) and light year (exactly 9,460,730,472,580,800 m).
Because every conversion routes through metres, converting inches to feet and back returns the original value exactly rather than drifting, which is not true of converters that chain approximations.
Examples
Metres to feet
Value
100
From
Metre
To
Foot
Result
328.08399 ft
100 divided by 0.3048. The foot is exactly 0.3048 m by definition, so the only imprecision is the rounding for display.
A marathon in miles
Value
42.195
From
Kilometre
To
Mile
Result
26.218757 mi
42,195 metres divided by 1,609.344. The familiar "26.2 miles" is this figure rounded to one decimal place.
A light year in kilometres
Value
1
From
Light year
To
Kilometre
Result
9.4607e+12 km
Values above a quadrillion switch to exponential notation, because 15 digits of zeros are harder to read than the exponent.
Frequently asked questions
Are the imperial conversions exact or approximate?
Exact. The 1959 international yard and pound agreement defined the inch as precisely 25.4 mm, which fixes the foot at 0.3048 m and the mile at 1,609.344 m. Every imperial figure here follows from those definitions rather than being a measured approximation.
Why is a nautical mile not the same as a mile?
Because it measures something different. A nautical mile is one minute of latitude, standardised at exactly 1,852 m, which makes chart work straightforward at sea. A statute mile of 1,609.344 m comes from Roman land measurement and has no relationship to the Earth’s geometry.
Why does the result switch to exponential notation?
Above a quadrillion or below a millionth, a decimal figure becomes a wall of zeros that is harder to read and easy to miscount. Light-year conversions cross that threshold immediately.
Does converting back and forth lose accuracy?
Not meaningfully. Every conversion routes through metres rather than chaining unit-to-unit approximations, so a round trip returns the original value to floating-point precision.