Length Converter

Instantly convert Length between SI and common engineering units including Meter (m), Kilometer (km), Decimeter (dm), Centimeter (cm). No formula lookup required.

Convert

About

Value × conversion factor to SI base (temperature uses affine offset), then restored to target unit.

Bidirectional conversion with unit swap supported.

Length Converter schematic

Fundamentals

Length is a basic physical quantity for measuring the relevant object; unit conversion unifies dimensions across standards, drawings and test data.

This tool uses Meter (m) as the base unit and scales the input by each unit's factor to the target; temperature and similar quantities use affine conversion $y=a x+b$. All factors are relative to SI.

History

Measurement of Length has a long history: ancient standards used body parts (cubit, foot) or nature (sundials, water clocks); the metric system (1790s) and SI (1960) unified global measurement.

Engineering applications

In mechanical design, trade, international drawings and test data, Length must often be converted between customary units such as Meter (m) and SI to keep dimensions consistent.

Glossary

Base unit	Reference unit, usually SI (e.g. Meter (m)).
Conversion factor	Proportional factor between a unit and the base.
Linear / affine	Most units are linear; temperature needs an offset (affine).

How to use

Enter the value to convert in the Value box.
Pick the source and target units from the From / To dropdowns.
Click Convert; the result shows below. Use ⇅ to swap units.

Formula notesUnit conversion (length): 长度：1 km = 1000 m，1 in = 25.4 mm，采用线性比例换算。

Formula · Worked Example · Knowledge

Formula

Length conversion uses the metre (m) as base; each unit's factor $a$ satisfies $\text{value}_{\text{SI}}=a\times\text{value}_{\text{unit}}$. E.g. $1\ \text{in}=0.0254\ \text{m}$, $1\ \text{ft}=0.3048\ \text{m}$, $1\ \text{mi}=1609.344\ \text{m}$. Conversion:
$$x_{\text{target}}=\frac{a_{\text{src}}}{a_{\text{target}}}\,x_{\text{src}}$$

Worked Example

Convert $1\ \text{m}$ to inches:

$$x_{\text{in}}=\frac{1}{0.0254}\approx39.37\ \text{in}$$
So $1\ \text{m}\approx39.37\ \text{in}$; $1\ \text{ft}=12\ \text{in}=0.3048\ \text{m}$.

Key Points

SI base unit of length is the metre (m); decimal multiples: km, cm, mm, μm, nm.
Imperial in/ft/yd/mi have fixed ratios to SI: 1 in = 25.4 mm, 1 ft = 304.8 mm, 1 mi = 1609.344 m.
This tool covers 13 length units with bidirectional conversion and unit swap.

Parameters

Supported units

Unit	Base factor
Meter (m)
Kilometer (km)
Decimeter (dm)
Centimeter (cm)
Millimeter (mm)
Micrometer (µm)
Nanometer (nm)
Inch (in)
Foot (ft)
Yard (yd)
Mile (mi)
Nautical mile (nmi)
Mil (mil)

Applications

Unified unit conversion in science/eng.
Teaching and dimensional checks
Standardising reported data

FAQ

What formula does this tool use?

This tool computes per ISO / AGMA / ASME standard formulas: Value × conversion factor to SI base (temperature uses affine offset), then restored to target unit.

How accurate are the results?

Results match input precision, based on SI units and common engineering approximations; for critical duty re-check with a safety factor.

Where is it used?

Unified unit conversion in science/eng.