How do I convert km to mm?

Use the formula shown above or enter a value to see km converted to mm instantly.

What is the formula for km to mm?

The converter calculates mm by applying the category-specific conversion factor for Length.

When should I use km vs mm?

km and mm are both part of the Length category; pick the unit that matches your measurement context (e.g., scale, region, or industry standard).

Length Converter & Reference

Convert km to mm

Use the live converter below to translate between Kilometer (km) and Millimeter (mm). Scroll further for quick examples, formula tips, and related units.

Formula insight: Most unit conversions use a simple multiplication or division by a conversion factor. The calculator shows the exact formula used.

Convert

km → mm

Kilometer

Millimeter

1,000,000

Rounded result (4 decimals max)

Formula

1 km = 1,000,000 mm

Conversion sourcesTap or click to view references

The International System of Units (SI) — NIST Special Publication 330
National Institute of Standards and Technology (NIST). The SI Brochure (SP 330) is the definitive English edition of the BIPM SI tables. NIST’s edition lists the official constants and conversion factors tying inch-pound units to SI, which SwapUnits applies for length, mass, temperature, pressure, volume, and related conversions. See /standards/nist-si-tenfold for the complete decimal multiple/submultiple table. View source · View SI table

Results update as you type. Swap the direction to convert back from mm to km.

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km to mm quick table

Multiply any row by the same factor to scale results. Use the converter above to enter exact values with your own units.

Kilometer (km)	Millimeter (mm)
0.25 km	250,000 mm
0.5 km	500,000 mm
1 km	1,000,000 mm
2 km	2,000,000 mm
5 km	5,000,000 mm
10 km	10,000,000 mm
25 km	25,000,000 mm
100 km	100,000,000 mm

mm back to km

Keep the reciprocal handy when double-checking calculations or undoing a conversion.

Millimeter (mm)	Kilometer (km)
0.25 mm	0 km
0.5 mm	0 km
1 mm	0 km
2 mm	0 km
5 mm	0 km
10 mm	0 km
25 mm	0 km
100 mm	0.0001 km

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