⚡ Free Online Electrical Tools
Free online electrical tools — Ohm's law, wattage, electricity cost, LED resistor, wire size, resistor color code, and more. Instant, browser-based, no signup.
10 tools available · 100% free · No signup required
Ohm's Law Calculator
Ohm's Law Calculator solves voltage, current, resistance, and power online for free. Enter any two values to instantly get the other two.
Wattage Calculator
Wattage Calculator finds power in watts from volts and amps online for free. Multiply voltage by current to get watts and kilowatts instantly.
Electricity Cost Calculator
Electricity Cost Calculator estimates the running cost of any appliance online for free. Enter watts, hours, days, and your rate to see daily and total cost.
Battery Life Calculator
Battery Life Calculator estimates how long a battery lasts online for free. Divide battery capacity in mAh by device current draw to get runtime in hours.
LED Resistor Calculator
LED Resistor Calculator finds the right current-limiting resistor for an LED online for free. Enter supply voltage, LED voltage, and current to get the resistor value.
Voltage Divider Calculator
Voltage Divider Calculator finds the output voltage of a two-resistor divider online for free. Enter Vin, R1, and R2 to get Vout, current, and power.
Power Factor Calculator
Power Factor Calculator finds power factor from real and apparent power online for free. Enter watts and VA to get power factor, reactive power, and phase angle.
Wire Size Calculator
Wire Size Calculator recommends an AWG copper wire gauge online for free. Enter current, distance, voltage, and drop limit to size the wire by ampacity and voltage drop.
Resistor Color Code Calculator
Resistor Color Code Calculator decodes 4-band and 5-band resistors online for free. Select each band colour to get the resistance value and tolerance instantly.
Capacitor Code Calculator
Capacitor Code Calculator decodes 3-digit capacitor codes online for free. Enter a code like 104 to get the value in pF, nF, and µF plus the tolerance.
Electrical work rewards getting the numbers right the first time, because a wrong resistor value or an undersized wire is not just inconvenient — it can be a safety hazard. This collection of electrical tools puts the everyday calculations an electrician, hobbyist, or electronics student reaches for into one place: Ohm's law, power and wattage, running cost of an appliance, the resistor a given LED needs, and the reference tables for reading resistor and capacitor color codes. Everything runs directly in your browser, so you can check a figure on the bench or on-site without an app or an account.
From first principles to real bench work
Start with Ohm's law to find the missing value among voltage, current, and resistance, then move to the wattage calculator to size a power supply or check that a component stays within its rating. Planning an install? The electricity-cost calculator turns an appliance's power draw and your tariff into a monthly figure, and the wire-size tool helps you pick a gauge that carries the current safely. For electronics tinkerers, the LED resistor calculator and the resistor and capacitor code readers remove the guesswork that leads to blown parts.
Built for accuracy and safety
Each calculator uses the standard formulas taught in electrical courses and applies clear input validation, so an impossible entry shows a neutral prompt rather than a misleading result. Lookup-based tools such as wire sizing and color-code reading use recognised reference tables and flag out-of-range values instead of guessing a nearest match. These tools are excellent for planning, learning, and double-checking, but always follow your local electrical code and consult a qualified electrician before carrying out mains work.