Conversion and calculation toolsbuilt with the source shown.
Every calculator on this site displays its formula, its standard reference, and a worked example — not just an answer box.
Conversions
Area Converter — m², ft², acres, hectares
Energy Converter — joules, kWh, calories, BTU, eV
Length Converter — cm, inches, feet, metres, km, miles
Power Converter — W, kW, HP, BTU/hr, tons of refrigeration
Pressure Converter — PSI, bar, kPa, Pa, atm, mmHg
Speed Converter — km/h, mph, m/s, knots, Mach
Temperature Converter — °C, °F, Kelvin
Volume Converter — litres, gallons, ml, fl oz, cups
Weight & Mass Converter — kg, lbs, oz, grams, stones
Engineering
LED Resistor Calculator — solve for Vsupply, Vf, forward current or R from the other three
Ohm's Law Calculator — solve for V, I, R or P from any two known values
Resistor Color Code Calculator — decode band colors to resistance, or look up colors for a value
Series & Parallel Resistor Calculator — equivalent resistance for 2 or 3 resistors, with a merge animation
Voltage Divider Calculator — solve for Vin, R1, R2 or Vout from the other three
Developer Tools
Base64 Encoder & Decoder — encode/decode text or files, drag-and-drop supported
JSON Formatter & Validator — format, validate and minify JSON
Scientific
Percentage Calculator — X is what % of Y, X% of Y, and percent change