Unit Conversion Guides
Detailed explanations of unit systems, conversion principles, and common points of confusion. Useful background for engineers, students, and anyone who needs to work across unit systems.
SI vs Imperial Units: A Complete Guide
Two major unit systems divide the world: SI (the metric system) and the imperial system. Engineers, scientists, and tradespeople encounter both daily. This guide explains where each system came from, what makes them different, when each is appropriate, and which conversions matter most in practice.
SI (the metric system) is the international standard used by every country except the US, Liberia, and Myanmar for everyday measurement.
Updated March 2026
US Gallon vs Imperial Gallon: What's the Difference?
The word 'gallon' refers to two different volumes depending on where you are. The US gallon is 3.785 liters; the imperial (UK) gallon is 4.546 liters — about 20% larger. Getting this wrong matters for fuel economy comparisons, brewing recipes, shipping, and any cross-border volume calculation.
1 US gallon = 3.785411784 liters (exact by US legal definition).
Updated March 2026
Mass vs Force: Understanding the Difference
Mass and force are often confused in everyday language — we say something 'weighs' 70 kg when technically we mean its mass is 70 kg and its weight (force) is about 686 newtons. This distinction matters in physics, engineering, and any context where gravity varies or unit systems are mixed. Understanding it also explains why the pound is one of the most ambiguous units in common use.
Mass is a measure of how much matter an object contains. SI unit: kilogram (kg). It does not change with gravity.
Updated March 2026
Temperature Conversion Explained: Celsius, Fahrenheit, and Kelvin
Temperature scales are unlike most unit conversions — they involve addition and subtraction as well as multiplication. This guide explains why the three major scales exist, what zero means on each, the exact conversion formulas, and the most common mistakes people make when converting temperatures.
Temperature conversions are affine (not purely multiplicative) because the scales have different zero points.
Updated March 2026
Common Pressure Units: PSI, Bar, kPa, atm, and MPa Explained
Pressure is force per unit area, and its units reflect the different industries and national standards that have evolved over centuries. This guide explains what each common pressure unit means, where it is used, and how to convert between them accurately.
PSI (pounds per square inch) dominates in US industry, automotive, and plumbing.
Updated March 2026
Torque Units Explained: Newton-Metres vs Pound-Feet vs Pound-Inches
Torque is a rotational force — the tendency of a force to cause rotation about an axis. It appears in fastener specifications, engine output ratings, and electric motor datasheets. This guide explains what torque units mean, how to convert between them, and the surprisingly easy mistake that can strip a bolt or damage an engine.
Torque = Force × Lever arm length. The SI unit is the newton-metre (N·m).
Updated March 2026
Binary vs Decimal Data Units: Bytes, Kibibytes, and Why 1 GB ≠ 1 GiB
A '1 TB' hard drive shows as 931 GB in Windows. A '16 GB' RAM stick looks like 15.3 GB in macOS. These discrepancies exist because storage manufacturers count bytes in powers of 10 while operating systems traditionally count in powers of 2. This guide explains both systems, their prefixes, and which to use when.
Decimal prefixes (KB, MB, GB, TB) use powers of 10: 1 GB = 1,000,000,000 bytes. Used by storage manufacturers and network speeds.
Updated March 2026
Tonne vs Ton: Metric Ton, Short Ton, and Long Ton Explained
Three different units are all called 'ton' in everyday speech, yet they differ by up to 12%. In shipping, agriculture, mining, and international trade, using the wrong 'ton' can mean significant discrepancies. This guide explains each variant, gives exact conversion factors, and tells you which is used where.
Metric tonne (t): 1,000 kg = 2,204.62 lb. The SI standard; used internationally in trade and science.
Updated March 2026
How we verify content
All conversion factors are sourced from NIST, SI, and ISO publications. Read our full methodology →