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Foundations and measurement history
Start with SI, base units, prefixes and the ideas behind measurement.
Open learning guides ↗ ARTICLESPractical conversion explainers
Short, useful answers for the questions people actually search.
Read articles ↗ FAQCommon questions, answered directly
Resolve ambiguity around metric, imperial, binary and reciprocal units.
Browse FAQ ↗Featured reference
All articles ↗What is a unit? A practical guide
Why every measurement needs a unit, the difference between base and derived units, and why SI exists.
Read guide ↗ DataWhy KB and KiB are different — and why it matters
Disk drives advertise GB, but your OS reports GiB. This article explains the 1000-vs-1024 divide.
Read guide ↗ LengthMetric vs Imperial: which countries still use imperial?
A quick map of who uses which — and where metric beats imperial at scale.
Read guide ↗ TemperatureCelsius to Fahrenheit explained — the formula and the intuition
F = C × 9/5 + 32. Here is why that formula is what it is.
Read guide ↗ SpeedWhat is a knot, and where did it come from?
A nautical mile per hour, measured by counting knots in a rope.
Read guide ↗ TimeWhy 29 days in February? The Roman calendar mess
From Numa to Caesar to the Gregorian reform — and why this means "year to day" conversions have caveats.
Read guide ↗ PressureHow pressure measurement evolved — from Torricelli to psi
Why psi and kPa and bar are all 1 atm apart by design.
Read guide ↗ EnergyJoule vs calorie vs kWh — which energy unit wins?
Why your electric bill uses kWh, your food label uses kcal, and your physics class uses joules.
Read guide ↗Ready to calculate?
Open a converter with the context still fresh.