How to Convert Units of Measurement
Unit conversion is the process of expressing a quantity in a different unit by multiplying or dividing by a conversion factor. The key principle: multiplying by a conversion factor is the same as multiplying by 1 — the value doesn't change, only its representation. Temperature is the exception, requiring addition or subtraction as well.
Last updated: March 31, 2026
The Formula
Value in new unit = Value in old unit × Conversion Factor Celsius to Fahrenheit: F = (C × 9/5) + 32 Fahrenheit to Celsius: C = (F − 32) × 5/9 Celsius to Kelvin: K = C + 273.15
Variable Definitions
| Symbol | Name | Description |
|---|---|---|
| CF | Conversion Factor | The ratio between two equivalent quantities in different units — e.g. 2.54 cm per inch |
| C / F / K | Temperature Scales | Celsius, Fahrenheit, and Kelvin — temperature conversions require both multiplication and addition |
Step-by-Step Example
Convert 5 feet 9 inches to centimetres, and 98.6°F to Celsius.
Given
Solution
- 1Convert 5 feet to inches:
5 × 12 = 60 inches - 2Total inches:
60 + 9 = 69 inches - 3Convert inches to cm:
69 × 2.54 = 175.26 cm - 4Convert 98.6°F to Celsius:
C = (98.6 − 32) × 5/9 = 66.6 × 5/9 = 37°C
5 ft 9 in = 175.26 cm. 98.6°F = 37°C (normal body temperature).
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Common Mistakes to Avoid
Dividing instead of multiplying (or vice versa) — always check: if converting to a smaller unit, the number should get bigger.
Using an imprecise conversion factor — 1 mile ≈ 1.6 km is fine for estimation but use 1.60934 for precision.
Applying the linear formula to temperature — Celsius to Fahrenheit needs both multiplication AND addition; you cannot just multiply by a single factor.
Mixing unit systems mid-calculation — keep everything in metric or everything in imperial until the very last step.