Electrical Calculators
Electrical Calculators
Our free electrical calculators cover the most common calculations for homeowners, students, electricians, and electronics hobbyists — from Ohm's Law and wire sizing to electricity cost and LED resistors.
Ohm's Law and Basic Circuits
Almost every electrical calculation starts with Ohm's Law: V = I × R (voltage equals current times resistance). From this single relationship, you can derive the power formula P = V × I, and solve for any unknown in a DC circuit given two known values.
Wire Sizing and Voltage Drop
Choosing the correct wire gauge is one of the most safety-critical decisions in electrical work. Undersized wire overheats, creating a fire risk. Our wire gauge calculator recommends the minimum AWG for a given load and run length, while our voltage drop calculator shows how much voltage is lost over long wire runs.
Waste Factors and Safety Margins
| Application | Typical safety margin |
|---|---|
| Branch circuit breaker | Load no more than 80% of breaker rating |
| Service entrance / panel | Size at 125% of calculated load |
| Wire ampacity | Derate for conduit fill, temperature, and run length |
| Motor loads | Size wire at 125% of full-load current |
AC vs. DC Electricity
Most household circuits use alternating current (AC) at 120 V or 240 V (North America) or 230 V (Europe/Australia). Batteries and electronics use direct current (DC). Power formulas differ slightly — AC circuits have power factor to consider. Our calculators note where AC vs. DC matters.
Working Safely with Electricity
Always turn off the breaker and verify with a non-contact voltage tester before working on any circuit. For any work beyond replacing outlets and switches, consult a licensed electrician and obtain the required permits. These calculators are for estimation and educational purposes only and do not substitute for professional electrical advice.