Exact factors · controlled display rounding
Traceable Length Unit Converter
Convert a curated set of SI and non-SI length units with exact rational factors. Results are rounded once to 15 significant digits; decimal point, decimal comma, signs and scientific notation are supported.
Conversion model
×ターゲット = xソース × kソース / kターゲット
Each k is the exact number of metres per unit shown below. Input is parsed as an integer coefficient and a power of ten. Conversion uses integer rational arithmetic; only the displayed result is rounded, to 15 significant digits using round-half-up. Scientific notation is used outside the fixed-display range. A displayed value is therefore not evidence of measurement uncertainty or significant figures.
| ユニット | Exact metres per unit k | 基礎 |
|---|---|---|
| Å | 10⁻¹⁰ m | BIPM historical name for an SI submultiple |
| nm | 10⁻⁹ m | SI prefix |
| µm | 10⁻⁶ m | SI prefix |
| µin | 2.54×10⁻⁸ m | 10⁻⁶ international inch |
| ミル | 2.54×10⁻⁵メートル | 10⁻³ international inch |
| mm | 10⁻³ m | SI prefix |
| cm | 10⁻² m | SI prefix |
| で | 0.0254メートル | International inch, exact |
| フィート | 0.3048メートル | International foot, exact |
| ヤード | 0.9144メートル | International yard, exact |
| m | 1メートル | SI基本単位 |
| km | 10³ m | SI prefix |
| mi | 1609.344メートル | 5280 international feet, exact |
| nautical mile | 1852 m | BIPM Table 8 |
Authoritative scope
について BIPM SI Brochure, 9th edition, version 4.01, updated 2026 defines the SI and prefixes and lists 1 Å = 10⁻¹⁰ m and 1 nautical mile = 1852 m. The metre definition fixes the numerical value of the speed of light in vacuum c at 299 792 458 when expressed in m·s⁻¹; equivalently, one metre is the path travelled by light in vacuum in 1/299 792 458 second.
NIST SP 811 Appendix B documents the international yard as exactly 0.9144 m and foot as exactly 0.3048 m; inch, mile, mil and microinch follow exactly. NIST states that the U.S. survey foot became obsolete on 2023-01-01 except for historical and legacy applications. This converter therefore means the international foot and international mile; it does not silently process legacy survey-foot data.
Why the pipe and application tables were removed
DN and NPS are nominal designations, not length units. Their outside diameters depend on the governing product standard and scope. For example, ASME B36.10-2022 covers welded and seamless wrought steel pipe, while other products and materials use other standards. The former unsourced “DN (mm) ↔ NPS” table was therefore removed from this generic converter. Likewise, surface roughness, vibration displacement and tolerances require their quantity definition, statistic and governing standard—not merely a length factor.
Former defects corrected
The previous page used parseFloat, rejected decimal comma through type=number, accepted numeric prefixes in malformed input, and rounded ordinary outputs to only two or four decimal places (for example 1 m became 39.37 in). Overflow showed unexplained dashes. Default 1000 mm, the unscoped pipe table, approximate factors presented beside exact factors, subjective claims about the metre and unsupported application ranges were removed.
