Electrical calculators
Works in your browser. Nothing is uploaded.Ohm’s law and power
Type any two of volts, amps, ohms and watts to work out the other two.
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Pick a unit beside each value, or type the number with its prefix, like 4.7k, 4k7 or 20m.
Type any two. The other two follow.
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Electrical calculators
Resistor color codeBands to ohms and back.Ohm’s law and powerVolts, amps, ohms and wattsVoltage drop and cable sizeThe drop over a run, and the smallest cable within itWire sizesAWG, mm², kcmil and diameterLED resistorThe resistor an LED needsSMD codesResistor and capacitor markings555 timerAstable and monostableBattery runtimeHow long a battery lasts
How to use it
- Type two values
Any two of voltage, current, resistance and power, each in the unit you pick.
- Read the other two
They fill in, marked Worked out, with the formula used.
- Change one
The two values you typed last are kept; the other two follow.
Tips
- Heater or kettle
A 2 kW kettle on 230 V draws about 8.7 A. A 1.5 kW heater on 120 V draws 12.5 A.
- Fuse for a plug
Watts ÷ volts gives the current: a 3 A plug fuse suits up to about 690 W on 230 V.
- Heat in a resistor
Current and resistance give the watts a resistor turns to heat. Pick one rated at twice that.
In the app
Electrical calculator in Angle Meter
- Ohm’s law, AC power and motor current
- Voltage drop and wire sizes
- Series and parallel parts and voltage dividers
- Drawn, list or multimeter screens
Get it onGoogle PlayComing soon to the App Store
Electrical calculator guide ›