The Unit Conversion Cheat Sheet: cm to inches, kg to lb, °F to °C

The three you'll use most: 1 inch = exactly 2.54 cm, 1 kilogram ≈ 2.205 pounds, and °F = (°C × 9/5) + 32. Those cover the vast majority of everyday conversions between the US customary system and the metric system the rest of the world uses. Below is a scannable reference table plus the exact formulas. When you need a different unit or a number that isn't on the chart, the Unit Converter handles length, weight, temperature, volume, and more in one place.

Quick reference table

Factors are based on the internationally defined values maintained by NIST. The inch-to-centimeter and pound definitions are exact; others are rounded for everyday use.

How do you convert cm to inches?

There are exactly 2.54 centimeters in one inch — an exact international definition, not a rounded number. So to go from inches to centimeters, multiply by 2.54; to go from centimeters to inches, divide by 2.54 (or multiply by 0.3937). Example: a 27-inch monitor is 27 × 2.54 = 68.6 cm wide diagonally.

How do you convert kg to lb?

Multiply kilograms by about 2.20462 to get pounds, or divide pounds by that figure to go the other way. The everyday shortcut: double the kilograms and add 10%. For 70 kg, double to 140 and add 14 → about 154 lb, which matches the exact answer of 154.3 lb. Close enough for the grocery store.

How do you convert °F to °C?

Temperature is the one conversion that isn't a simple multiply, because the two scales start at different zero points. The formulas:

A handy mental trick for °C → °F: double the Celsius number and add 30 for a rough estimate. 20 °C → about 70 °F (exact is 68 °F). It's not precise, but it tells you whether to grab a jacket.

Why the US uses different units

The United States is one of only three countries — alongside Liberia and Myanmar — that hasn't fully adopted the metric system for everyday use. That's why a US recipe lists cups and Fahrenheit while a European one lists grams and Celsius, and why the same bag of flour can carry both. The science and medical worlds in the US actually run on metric; it's mainly consumer life that stayed customary. Knowing the handful of factors above bridges the two systems for almost anything you'll meet day to day, from a European furniture listing in centimeters to a running app reporting kilometers.

The four conversions worth memorizing

If you only commit a few to memory, make them these high-frequency ones:

• 1 inch = 2.54 cm — screens, lumber, body height.
• 1 kg ≈ 2.2 lb — luggage limits, body weight, groceries.
• 1 mile ≈ 1.6 km — driving and running distances.
• °F = (°C × 9/5) + 32 — weather, cooking, fevers.

Everything else you can look up in seconds — and rounding errors creep in fast when you chain conversions by hand, which is exactly where a tool earns its keep.

Convert anything instantly

This sheet covers the common cases, but for odd units, long decimals, or back-and-forth conversions, the Unit Converter does it instantly and shows the factor it used — no rounding errors, no sign-up. Bookmark it next to this page and you'll never second-guess a conversion again. If you're working with body-weight numbers, our guide What is a healthy BMI for your height? uses these same kg-and-cm conversions in context.

Frequently asked questions

How many centimeters are in an inch?

Exactly 2.54 centimeters. It's an exact definition, so multiply inches by 2.54 to get centimeters, and divide centimeters by 2.54 to get inches.

How do you convert kilograms to pounds?

Multiply kilograms by about 2.20462. For a quick mental estimate, double the kilograms and add 10% — that lands very close.

What is the formula for Fahrenheit to Celsius?

Subtract 32, then multiply by 5/9. To reverse it, multiply Celsius by 9/5 and add 32. Water freezes at 0 °C, which is 32 °F.