Electrical
Electrical tools on UniTools: ohms law and power, cable size and voltage drop and more.
This section covers the arithmetic that comes up constantly in wiring work and in electronics: Ohm's law, power to current, cable and breaker sizing, voltage loss over a long run, the series resistor for an LED and the colour code on its bands.
The second half is about light and supply: how many lumens a room needs, how many fittings that is, what generator will carry a house with a pump, and how many solar panels cover a day's consumption.
Tools in this category
Ohm's Law Calculator
Finds all four quantities from any two known values, with resistance shown in whichever unit reads most naturally.
Watts Amps Volts Calculator
Converts power to current and back for single-phase and three-phase supplies, and suggests a breaker rating.
kVA to kW Calculator
Links apparent and real power through the power factor and shows the resulting current at both 220 and 380 volts.
Voltage Drop Calculator
Computes the voltage lost along a cable from length, cross-section and current, checks it against the three percent limit and suggests a size.
Wire Size Calculator
Picks a cable cross-section for a given current, allowing for conductor material and installation method.
Resistor Colour Code
Decodes the value from four or five colour bands and shows the range the tolerance allows.
LED Resistor Calculator
Sizes the series resistor from supply voltage, LED forward drop and working current, and picks the nearest standard value.
Lumens to Lux Calculator
Converts luminous flux into illuminance over an area and back, and shows the LED and incandescent wattage that would produce it.
Room Lighting Calculator
Works out the luminous flux a room needs for its purpose, how many lamps that means and the total wattage, with a ceiling-height correction.
Power Factor Calculator
Computes the power factor, the reactive power behind it and the capacitance needed to reach a target figure.
Battery Life Calculator
Estimates how long a device will run on a battery of a given capacity, allowing for converter efficiency.
Solar Panel Calculator
Sizes the array, the battery bank and the inverter for a given daily consumption.
Generator Sizing Calculator
Works out the generator rating a load needs, allowing for motor starting surge, power factor and headroom, plus fuel use.
Transformer Calculator
Turns ratio, winding currents, secondary turns and an indicative core cross-section.
Three-Phase Power Calculator
Real, apparent and reactive power for a three-phase supply from line voltage, current and power factor.
Related categories
FAQs
How do I choose a cable size?+
From the design current and the installation method, not from appliance wattage. Size the cable first, then the breaker to match — the breaker protects the cable, not the load.
How many amps in a kilowatt?+
About 4.5 at 220 volts and only 1.5 at 380 on a three-phase supply, because the load spreads across three phases.
What is the difference between kW and kVA?+
Kilowatts are useful output; kilovolt-amps are the total the equipment must pass. The ratio between them is the power factor.
Can I rely on these for an installation?+
They give the right order of magnitude and follow the wiring code and lighting standards. A full electrical design for a house is still a job for a qualified engineer.