Comparisons
When the question is “which one should I use?”, you don’t want a tool — you want a recommendation. Each comparison lays out the underlying trade-off, walks through worked examples, and finishes with a clear answer for the typical case.
Celsius vs Fahrenheit: why two scales survived
Where each came from, the conversion formula's algebra, and the one rare context where Fahrenheit's resolution is actually useful.
Kilograms vs pounds: the 2.20462 you can never quite remember
The factor, the history, the mental shortcut, and the two cases where the difference matters.
PNG vs JPG: when to use which
Lossless vs lossy, alpha vs none, file-size trade-offs.
Wei vs Gwei: which unit to use when
Two Ethereum subunits, both denominated in powers of ten. Where each is the right choice.
UTC vs GMT: are they the same?
Same clock on the wall. Different definition behind it. Here's the distinction that matters.
RGB vs CMYK: additive vs subtractive, screens vs print
Different mediums, different math, different gamuts. Why brilliant orange on monitor turns muddy in print.
SHA-256 vs MD5: never use MD5 for security
MD5 has been cryptographically broken since 2004. Why it persists, where it's acceptable, what to use instead.
Bitcoin vs Ethereum: different goals, different tradeoffs
Smart contracts vs digital gold, proof-of-stake vs proof-of-work, programmability vs scarcity.
JPG vs WebP: 25% smaller files at the same quality
WebP beats JPG on file size at equivalent visual quality. The catch (browser support) is mostly gone.
BMI vs body fat percentage: which actually tells you something useful?
BMI is fast and free; body fat is informative but harder to measure. When each is the right tool.
US cup vs UK cup: the kitchen measurement that varies by country
A US cup is 237 ml. A UK cup is 284 ml. An Australian cup is 250 ml. The 20% gap that ruins recipes.
Active dry vs instant yeast: when to bloom, when to skip
Same fungus, different prep. Active dry needs blooming; instant doesn't. Conversion ratios and when fresh yeast wins.
SHA-1 vs SHA-256: SHA-1 is dead, but Git still uses it
First practical SHA-1 collision in 2017. Why TLS dropped it, why Git keeps it (with caveats), and the SHA-256 migration roadmap.
Celsius vs Kelvin: same step, different zero
1 K = 1°C in size. They differ only in where zero sits. Why Kelvin is mandatory in physics and Celsius is fine for everyday.
Markdown vs HTML: when each is the right answer
Markdown is HTML's writer-friendly source. HTML is markdown's expressive endpoint. They're not competing tools.
UUID v4 vs v7: pick v7 for database keys
v4 is pure random — 122 bits. v7 is timestamp + random — sortable by creation time. Why v7 destroys v4 for DB performance.
Fan oven vs conventional: when to use which (and the −20°C rule)
Fan ovens cook 20°C hotter at the same setting. When convection wins and when delicate bakes need conventional.
15- vs 30-year mortgage: which is actually cheaper?
A 15-year saves ~55% of total interest but raises the monthly payment ~40%. When the savings stop being worth the cash-flow cost.
DPI vs PPI: the difference that costs designers money
DPI is a printer property. PPI is an image property. They're conflated — until you send a 72-PPI image to a 300-DPI press.
US vs EU shoe size: why every conversion table disagrees
EU is in Paris points (~⅔ cm). US is in barleycorns (⅓ inch). Both measure the last, not the foot. Why brand-specific charts disagree.
Cup vs gram: why your cookies keep failing
A cup of flour weighs 120-160 g depending on how you scoop. Grams are reproducible; cups aren't. Why serious bakers switched to weight.
Base64 vs base64url: two characters that matter
Base64 uses +, /, =. Base64url uses -, _, no padding. Why JWTs picked one, why emails picked the other.