A meter is the SI base unit of length, equal to approximately 3.281 feet or 1.094 yards. A yard is an imperial unit equal to exactly 0.9144 meters, originally based on the average length of a stride. They are close in size but not interchangeable without conversion.

Multiply kilometers by 0.621371 to get miles. For example, 10 km equals 6.214 miles. Conversely, multiply miles by 1.60934 to convert back to kilometers. A handy approximation is that 8 km is roughly 5 miles.

Divide the number of centimeters by 2.54 to get inches, since 1 inch is defined as exactly 2.54 centimeters. For example, 30 cm ÷ 2.54 = 11.81 inches. This is an exact definition, not an approximation.

Millimeters are best for small, precise measurements such as mechanical parts, screen dimensions, or rainfall amounts. Centimeters suit everyday human-scale measurements like height, clothing sizes, and furniture dimensions. Both are metric and convert easily by a factor of 10.

A nautical mile equals exactly 1,852 meters and corresponds to one arc-minute of latitude on Earth's surface, making it ideal for navigation at sea and in aviation. Speed over water and air is measured in knots, where 1 knot equals 1 nautical mile per hour.