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CalcLab

Length Converter

Convert between metric and imperial length units.
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No results yet — Enter values and run the tool to see results.

What is this converter?

Converts a length or distance between metric units (millimetre to kilometre) and imperial units (inch, foot, yard, mile). All conversions pass through the metre, the SI base unit of length.

Use it when:

  • A specification, drawing, or product listing uses units you do not work in.
  • You are reconciling metric and imperial measurements on the same project.
  • You need a quick, exact conversion without rounding it in your head.

Intended for: Anyone working across measurement systems — trades, engineering, travel, or education.

How is this calculated?

  1. Each supported unit is defined by a fixed conversion factor relative to one base unit for the quantity (for example, the metre for length).
  2. The value you enter is first converted from the source unit into that base unit by multiplying by the source unit's factor.
  3. The base value is then converted into the target unit by dividing by the target unit's factor.
  4. Because both factors are exact constants, the conversion is a single deterministic multiplication and division — the same input always produces the same output.

Formula

Factor conversion

Result = Value × (factor of source unit) ÷ (factor of target unit)

Each factor expresses that unit in metres, so both steps cancel to the target unit.

Example

Converting 5 metres to feet.

  1. 1 metre is exactly 1 metre (the base unit).
  2. 1 foot is exactly 0.3048 metres.
  3. 5 ÷ 0.3048 ≈ 16.4042.

Result: 5 metres ≈ 16.4042 feet.

Frequently asked questions

Are the imperial conversions exact or approximate?

Exact. Since 1959 the international yard has been defined as exactly 0.9144 metres, which makes the inch exactly 25.4 mm and the foot exactly 0.3048 m. Any approximation you see is display rounding only.

Which mile does this use?

The international statute mile of 1,609.344 metres. Nautical miles are a different unit and are not included in the length list.

Assumptions

What this converter takes as given:

  • Conversion factors are the internationally standardised definitions of each unit, not regional or historical variants.
  • The value you enter is treated as an exact quantity — no measurement uncertainty is carried through the conversion.
  • Results are rounded only for display; the underlying arithmetic uses full precision.

Limitations

What this converter cannot know or does not model:

  • The converter does not know the precision of your original measurement, so it cannot report significant figures for you.
  • Units that share a name but differ by region or era (for example, different definitions of a gallon or a ton) are offered only in the variants listed in the unit menu.
  • Very large or very small magnitudes are subject to the limits of double-precision floating-point arithmetic.

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