Question 1

What is a caliber in measurements?

Accepted Answer

A caliber is 0.01 inch (0.254 mm). Used primarily in firearms to measure bullet/barrel diameter. A .45 caliber gun has a 0.45-inch bore.

Question 2

How do I convert caliber to millimeters?

Accepted Answer

Multiply caliber by 0.254. Example: .45 caliber = 11.43 mm. Common: .22 cal = 5.6 mm, 9mm = .354 cal.

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.

cal to mm Converter

Frequently Asked Questions

Explore Financial Toolset

Compound Interest Calculator

Mortgage Calculator

Debt Payoff Calculator

Retirement Calculator