Metric vs. imperial, in brief
The metric system (meters, centimeters, kilometers) is built on powers of ten, so converting within it is just moving a decimal point. The imperial/US customary system (inches, feet, yards, miles) uses conversion factors rooted in historical measurement practices — 12 inches to a foot, 3 feet to a yard, 5,280 feet to a mile — which is why it needs an actual converter rather than mental math.
Common conversions worth memorizing
- 1 inch = 2.54 cm (exact, by international agreement since 1959)
- 1 foot = 30.48 cm
- 1 meter ≈ 3.28 feet
- 1 mile = 1.609 km
- 1 kilometer ≈ 0.621 miles
Worked example
A 6-foot-tall person is 6 × 30.48 = 182.88 cm tall, or about 1.83 meters.