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 to Amps and Amps to Watts
Converts watts and kilowatts to amps and back on 220 and 380 V AC and 12 or 24 V DC, shows the amps per kilowatt, and suggests a breaker no smaller than the current from the IEC 60898-1 range.
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
Works out cable voltage drop with the method in annex G of IEC 60364-5-52 — service resistivity and conductor reactance included — and checks it against the 3% limit for lighting and 5% for other loads.
Wire Size Calculator
Picks a cable cross-section for a given current, allowing for conductor material and installation method.
Resistor Color Code
Decodes the value from four or five colour bands with the tolerance range, and the digit codes printed on SMD resistors: 103, 1002, 4R7.
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 to illuminance over an area and back, compares the result with the home lighting norms of Russia's SP 52.13330 and shows the wattage of LED and incandescent lamps at the efficacies Wikipedia gives.
Room Lighting Calculator
Works out the flux and the number of lamps a room needs under Russia's SP 52.13330.2016 as amended in 2022 — 200 lx for living rooms and kitchens, 100 lx for corridors and bathrooms, 500 lx for a study — with a maintenance factor of 0.71, or 0.7455 for LEDs.
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
Works out how many panels cover a daily consumption at your sun hours and losses, what they yield and how big a battery bank the days of autonomy need at the allowed depth of discharge.
Generator Sizing Calculator
Works out the smallest generator rating from the running load with headroom and from the start-up of the largest motor — and says which of the two decides.
Transformer Calculator
Works out the turns ratio from the winding voltages, the primary and secondary currents at a given power, and the secondary turns from the primary's.
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.