What is a Conversion Factor?

A conversion factor is a number used to change one set of units to another. It represents the relationship between two units. For example, since 1 inch equals 2.54 centimeters, the conversion factor is 2.54.

Common Conversion Factors

• Length: 1 inch = 2.54 centimeters, 1 mile = 1.60934 kilometers
• Weight: 1 pound = 0.453592 kilograms, 1 ounce = 28.3495 grams
• Volume: 1 gallon = 3.78541 liters, 1 cup = 236.588 milliliters
• Temperature: Special formulas (see below)

The Basic Formula

New Value = Original Value × Conversion Factor
Example: Convert 10 inches to centimeters: 10 × 2.54 = 25.4 cm

Special Temperature Formulas

Unlike other conversions, temperature requires special formulas because the scales have different starting points (zero points).

Celsius to Fahrenheit

Formula: °F = (°C × 9/5) + 32
Example: 20°C = (20 × 9/5) + 32 = 68°F

Fahrenheit to Celsius

Formula: °C = (°F - 32) × 5/9
Example: 68°F = (68 - 32) × 5/9 = 20°C

Celsius to Kelvin

Formula: K = °C + 273.15
Example: 20°C = 20 + 273.15 = 293.15 K

Double-Check Your Work

Always verify conversions, especially in critical applications like medicine, engineering, or cooking. A small error can have significant consequences. Use estimation to check if your answer is reasonable.

Learn Common Conversions

Memorize frequently used conversions for quick mental calculations. For example, knowing that 1 inch ≈ 2.5 cm or 1 kg ≈ 2.2 pounds can be helpful for quick estimates.

Use Dimensional Analysis

For complex conversions, use dimensional analysis to ensure units cancel correctly. This helps prevent errors in multi-step conversions. Write out your units and make sure they cancel to give you the desired final unit.