Unit Conversion calculators
Unit conversion looks like the most trivial arithmetic on the internet, and it is responsible for a remarkable share of expensive mistakes — lost spacecraft, mis-dosed patients, under-ordered concrete and ruined cakes. These converters use exact defined factors rather than rounded shortcuts, route every calculation through a single SI base unit so nothing drifts, and flag the places where two units share a name but not a size: the two gallons, the three tons, the two horsepowers, the decimal and binary gigabyte.
16 calculators in this category
Most used unit conversion calculators
Why conversion factors should be exact, not approximate
Most imperial-to-metric factors are exact definitions rather than measurements. Since the 1959 international agreement the inch is exactly 25.4 mm and the pound exactly 0.45359237 kg, so a correctly performed conversion introduces no error at all. Every converter here stores each unit as its exact multiple of an SI base unit and converts in two steps — into the base, then out of it — rather than chaining pairwise ratios, which is where rounding drift accumulates.
The familiar shortcuts are convenient and lossy. Treating a mile as 1.6 km is 0.6% low; a kilogram as 2.2 lb is 0.3% high; a bar as one atmosphere is 1.3% low. None of these matters when you are estimating a journey, and all of them matter when the figure lands in a material order, a dosage, a structural load or a contract.
Squares, cubes and the errors they hide
Area and volume factors are the square and cube of the corresponding length factor, not the length factor itself. One foot is 0.3048 m, but one square foot is 0.0929 m² and one cubic foot is 0.0283 m³. Applying the linear factor to an area is wrong by a factor of about three, and to a volume by about eleven. Construction estimating is where this appears most often, usually as an order that is wildly wrong rather than subtly wrong.
Reciprocal scales are a related trap. Fuel economy in MPG rises as consumption falls, so converting to litres per 100 km means inverting the number, not scaling it. The same non-linearity explains why an improvement from 15 to 20 MPG saves more than three times as much fuel as an improvement from 40 to 50 MPG over the same distance.
Units that share a name but not a size
The imperial gallon is about 20% larger than the US gallon, so every derived pint, quart and fluid ounce differs too, and an imperial MPG figure flatters a car against its US rating. Three tons circulate in commerce — metric tonne, US short ton and UK long ton — spanning an 11% range. Two horsepowers are in active use, mechanical at 745.7 W and metric PS at 735.5 W. Storage sizes are quoted decimally by drive makers and binarily by operating systems, which is the entire explanation for a 1 TB disk reporting 931 GB.
Temperature is the one conversion that is not a simple ratio at all, because the scales have different zero points as well as different degree sizes. That also means a temperature and a temperature difference convert by different rules: a rise of 10 °C is a rise of 18 °F but also a rise of exactly 10 K. Confusing an interval with a point is the standard failure mode in thermal and HVAC specification work.
Every unit conversion calculator
Unit Conversion calculator questions
Are these conversions exact?+
The factors are exact wherever an exact definition exists, which covers essentially all length, mass, volume, area, force and energy units. Displayed results are rounded for readability, and a few figures — Mach number, average months, cooking densities — are inherently approximate and labelled as such.
Which gallon or ton does a figure use?+
Each unit is named in full in the dropdowns, so US and imperial gallons, and metric, short and long tons, are always distinguishable. If a source document does not say, treat the figure as unverified until it does.
Should I use MB or MiB?+
Use MiB, GiB and TiB when you mean powers of two, and MB, GB and TB when you mean powers of ten. The gap reaches 10% at the terabyte scale, which is enough to matter in capacity planning.
Why do cooking conversions depend on the ingredient?+
Because a cup measures volume and grams measure mass, so the answer scales with density. A cup of cocoa is about 85 g and a cup of honey about 340 g, so no single cups-to-grams factor can exist.