Unit Converter

How this works

Most converters ask you to pick a source unit and a target unit. That assumes you already know which target you want, which is often the thing you were trying to work out. This one converts into every unit in the category at once and highlights the one you typed into.

Every category except temperature is a linear scale, so conversion is value × fromFactor ÷ toFactor against a base unit. Temperature scales have different zero points, so those get explicit conversion functions instead of a factor.

Data: decimal and binary, side by side

This is the category worth the most attention, because the confusion is universal.

• Decimal prefixes step by 1000. kB, MB, GB, TB. This is what drive manufacturers print on the box, and it is the SI meaning of “kilo”.
• Binary prefixes step by 1024. KiB, MiB, GiB, TiB. This is what operating systems usually count in, because memory addressing is binary.

A “500 GB” drive holds 500,000,000,000 bytes, which is 465.66 GiB. Nothing is missing and nobody is lying. The two systems drift apart by 2.4% per prefix step, so it is 7.4% by the gigabyte and 10% by the terabyte.

The table separates the two families with a header rather than interleaving them, so you cannot accidentally read across from one to the other.

Ohm’s law solver

The electrical categories carry a four-field solver: volts, amps, ohms, watts. Fill in any two and it derives the rest from V = I × R and P = V × I.

It only ever fills blanks, never the field you are typing in, so it cannot fight you mid-entry. Where a pair is genuinely insufficient it says so instead of guessing.

Categories

Category	Base	Notable units
Data	byte	bit through PB, plus KiB through PiB
Voltage	volt	nV to MV
Current	ampere	pA to kA
Resistance	ohm	mΩ to GΩ
Power	watt	µW to GW, mechanical and metric horsepower, BTU/h
Energy	joule	eV, Wh, kWh, calorie, BTU
Length	metre	nm to km, inch, foot, yard, mile, nautical mile
Mass	kilogram	mg to tonne, ounce, pound, stone
Temperature	Celsius	Celsius, Fahrenheit, Kelvin, Rankine
Time	second	ns to years
Speed	m/s	km/h, mph, ft/s, knot
Pressure	pascal	kPa, MPa, bar, psi, atmosphere, mmHg

Precision

Values span an enormous range - an electronvolt and a kilowatt-hour sit in the same category, twenty-five orders of magnitude apart. Fixed decimal places would be useless at one end or the other, so the display switches to exponential notation beyond 10^15 and below 10^-6, and otherwise keeps enough significant figures that small values do not collapse to zero.

Sources

• SI prefixes and base units, and the IEC 80000-13 binary prefixes (kibi, mebi, gibi)
• International yard and pound agreement of 1959: inch = 25.4 mm exactly, pound = 0.45359237 kg exactly
• Nautical mile = 1852 m exactly, by international definition
• Mechanical horsepower = 745.6998715822702 W; metric horsepower (PS) = 735.49875 W
• Thermochemical calorie = 4.184 J; BTU (IT) = 1055.05585262 J

Limitations

• Linear scales only, temperature aside. Anything with a non-linear response, like decibels or pH, is not here and would be misleading if it were.
• No currency. Rates change; that belongs in the currency converter, which carries a verification date.
• Floating point. Conversions run in IEEE 754 doubles, so chained conversions at extreme magnitudes can drift in the last significant figure.
• The Ohm’s law solver assumes DC, or RMS values with a purely resistive load. Reactive circuits need impedance and a phase angle, which this does not model.

Disclaimer

This tool is provided as is, with no warranty of any kind, express or implied, including no warranty of accuracy, completeness or fitness for a particular purpose. Verify anything safety-critical against a primary reference. Electrical work in particular can be dangerous, and an arithmetic helper is not a substitute for a qualified electrician. Use entirely at your own risk.