Question 1

How many centimeters in an inch?

Accepted Answer

1 inch = 2.54 cm exactly (by international agreement since 1959). This is the key conversion factor for imperial/metric length.

Question 2

How do I convert cm to inches quickly?

Accepted Answer

Divide by 2.54 or multiply by 0.3937. Quick estimate: divide cm by 2.5 for approximate inches. 10 cm ≈ 4 inches.

Question 3

Is this conversion factor exact?

Accepted Answer

Metric-to-metric conversions are exact (1 km = 1000 m). Imperial-to-metric factors like 1 inch = 2.54 cm are exact by international agreement.

Question 4

Why do some countries use different units?

Accepted Answer

Historical reasons - the metric system spread from France after 1795. The US, UK, and a few others retained older systems. Science uses metric worldwide.

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