Data Size: Binary vs SI Units
This is the most common source of confusion in developer contexts. The SI system uses powers of 10: 1 MB = 1,000,000 bytes. The binary system uses powers of 2: 1 MiB = 1,048,576 bytes. Operating systems, storage vendors, and network tools are inconsistent about which they use. A 1 TB hard drive holds about 931 GiB. When you are calculating buffer sizes or file upload limits in code, know which system your API expects.
CSS Units: px vs rem vs em
- px: absolute pixels, device-dependent.
- rem: relative to the root font size (usually 16px). Preferred for font sizes and spacing because it respects user accessibility settings.
- em: relative to the current element's font size — compounds in nested elements and is harder to reason about.
A quick rule: 1rem = 16px, so 1.25rem = 20px, 0.875rem = 14px.
Temperature: Celsius and Fahrenheit
The formula most developers need: F = C × 9/5 + 32. Common reference points: 0°C = 32°F (freezing), 100°C = 212°F (boiling), 37°C = 98.6°F (body temperature), 20°C = 68°F (comfortable room).
Practical Use Cases
API rate limits often mix units inconsistently. Cloud storage pricing uses SI units. CSS design specs from designers are often in px and need to be converted to rem. A unit converter tool handles all of these without mental arithmetic.