Unit & Measurement Comparisons
Two units, side by side — what actually differs, which one to use, and how to convert between them.
A conversion tells you the number. A comparison tells you which unit you should have been using in the first place. These pages sit alongside MegaCalc's converters for the cases where the arithmetic is the easy part — where the real question is whether a specification written in one system means what you think it means in another, or why two “gallons” can differ by nearly twenty percent depending on which side of the Atlantic the document was written on.
Each comparison lays out both units in parallel, lists the differences that actually change decisions, and says plainly when each one is the right choice. Where a numeric conversion is useful, it links directly to the relevant converter so you can move from understanding to a number without hunting for it.
Miles per hour and kilometres per hour — which countries use each, and how to read a speed limit abroad
Feet and metres compared — where each is standard, and the exact factor that connects them
Pounds and kilograms compared — mass versus weight, and the exact conversion between them
Inches and centimetres compared — screen sizes, body measurements, and the exact 2.54 relationship
Grams and ounces compared — which ounce you mean, and why recipes disagree
Litres and gallons compared — and why a US gallon and a UK gallon are not the same size
Acres and hectares compared — land area in agriculture, real estate and forestry
Mach number and miles per hour — why Mach 1 is not a fixed speed
Knots and miles per hour — why aviation and shipping use a different speed unit
Stones and pounds — the British body-weight convention and how to read it
PSI and bar compared — tyre pressures, hydraulics, and the gauge-versus-absolute trap
Kelvin and Celsius compared — same size degree, different zero, and when the difference matters
Understanding the differences between metric and imperial measurement systems
The two most common temperature scales and when to use each
Comparing miles and kilometers for distance measurement
Understanding the difference between troy ounces (precious metals) and standard ounces
The difference between nautical miles used in navigation and regular statute miles
Why a UK gallon and a US gallon are not the same volume
Comparing the US short ton with the international metric ton
Comparing the US cup measurement with milliliters for cooking and baking