Length Converter

About the Length Converter

A length converter instantly transforms measurements between metric units (millimetres, centimetres, metres, kilometres), imperial and US customary units (inches, feet, yards, miles), and specialised units including nautical miles, light-years, and astronomical units. Length conversion is one of the most practically needed calculations in everyday life — required when shopping for imported products with different unit dimensions, following international recipes, reading scientific papers, planning construction projects, buying clothing and shoes from foreign retailers, and interpreting engineering specifications from different countries. The USA, Myanmar, and Liberia are the only countries still primarily using the imperial measurement system, making metric-to-imperial and imperial-to-metric conversion an essential cross-border communication skill. Our converter handles the full range from nanometres used in semiconductor fabrication to light-years used in astronomy — covering 20 units across all scales with 15-digit precision.

How It Works

All conversions route through the metre as the SI base unit. Exact conversion factors: 1 inch = 2.54 cm (exact by international agreement since 1959). 1 foot = 12 inches = 30.48 cm. 1 yard = 3 feet = 91.44 cm. 1 mile = 5,280 feet = 1,609.344 m. 1 km = 1,000 m = 0.621371 miles. 1 nautical mile = 1,852 m exactly. 1 astronomical unit (AU) = 149,597,870.7 km. 1 light-year = 9.461 x 10^15 m. Converting 5 feet 9 inches to centimetres: 5 x 30.48 + 9 x 2.54 = 152.4 + 22.86 = 175.26 cm. Converting 100 km to miles: 100 x 0.621371 = 62.14 miles.

Tips & Best Practices

• ✓Quick approximations: 1 metre ≈ 3.28 feet; 1 km ≈ 0.62 miles; 1 inch = 2.54 cm (exact); 5 miles ≈ 8 km (accurate to 1%).
• ✓Human height conversions: 5'0" = 152.4 cm; 5'6" = 167.6 cm; 5'10" = 177.8 cm; 6'0" = 182.9 cm; 6'2" = 187.96 cm.
• ✓Running distances: 5K = 3.107 miles; 10K = 6.214 miles; half marathon = 13.109 miles (21.098 km); marathon = 26.219 miles (42.195 km).
• ✓Screen sizes: always measured diagonally in inches in the USA but centimetres in some markets — a 55-inch TV = 139.7 cm diagonal.
• ✓Road signs: speed limits in km/h on European and most international roads, mph in the USA and UK. Highway 100 km/h = 62.1 mph; 70 mph = 112.7 km/h.
• ✓1 nautical mile = 1 minute of arc of latitude = 1.852 km exactly. Defined this way so navigators can use latitude degrees directly for distance calculation.
• ✓Clothing and shoe sizes often use different measurement systems — a European size 44 shoe corresponds to approximately 28 cm foot length. Converting dimensions helps with international online purchases.
• ✓Metric prefixes: nano (10^-9), micro (10^-6), milli (10^-3), centi (10^-2), kilo (10^3), mega (10^6), giga (10^9). A nanometre is 10^-9 metres — the scale of atoms and semiconductor transistors.

Who Uses This Calculator

International travellers reading road signs in unfamiliar unit systems. Engineers reading technical specifications from different countries. Online shoppers buying clothing and products with different sizing systems. Students completing physics, chemistry, and STEM homework. Athletes tracking performance across metric and imperial distances. Architects and builders working with international drawings and specifications. Scientists converting between measurement systems for research and publication.