ElectriCalc

What Is an Electrical Calculator?

An electrical calculator is an online tool that solves common electrical engineering equations -- Ohm's Law, power calculations, wire sizing, voltage drop, and component identification. Whether you are a homeowner wiring a new outlet, an electrician sizing cable for a subpanel, or a hobbyist building an LED circuit, electrical calculators eliminate manual math errors and provide instant, accurate results based on established formulas and NEC standards.

Electrical engineering calculations fall into three broad areas. Circuit analysis uses Ohm's Law (V = IR) and power equations (P = VI) to find unknown voltages, currents, resistances, or power dissipation given two known values. Wire and cable sizing ensures conductors can safely carry the required current over a given distance without excessive voltage drop or overheating -- critical for both NEC code compliance and efficient power delivery. Component identification covers resistor color codes, SMD markings, LED current limiting, and RC time constants for timing circuits.

ElectriCalc organizes fifteen free calculators into three categories: Ohm's Law (basic calculator, power calculator, voltage divider, current divider, series/parallel resistance), Wire and Cable (wire size, voltage drop, ampacity chart, wire resistance, conduit fill), and Resistor (color code decoder, SMD code calculator, LED resistor, RC time constant, inductor reactance). All tools run in your browser with no sign-up required and produce results with clear explanations of the formulas used.

About ElectriCalc

ElectriCalc provides free, accurate electrical engineering calculators for hobbyists, students, electricians, and engineers. All tools run in your browser with no sign-up required.

Ohm's Law: The Foundation of Circuit Analysis

Ohm's Law states that the current through a conductor between two points is directly proportional to the voltage across those points: V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms. This simple relationship underpins virtually all DC circuit analysis. Combined with Joule's Law for power (P = V × I = I² × R = V² ÷ R), these four equations let you solve for any unknown given two knowns. In practice, Ohm's Law applies to resistive (linear) components; non-linear devices like diodes and transistors require additional models.

Wire Sizing and Voltage Drop

Selecting the correct wire gauge is critical for both safety and performance. In the US, wire sizes follow the American Wire Gauge (AWG) standard — counter-intuitively, lower AWG numbers indicate thicker wire. A 14 AWG copper wire is rated for 15 A, 12 AWG for 20 A, and 10 AWG for 30 A under standard residential installation conditions. Voltage drop occurs across wire resistance: V_drop = I × R_wire, where R_wire increases with wire length and decreases with wire cross-section. The NEC recommends limiting voltage drop to 3% for branch circuits and 5% total from service panel to outlet. Long wire runs (for solar panels, subpanels, or EV chargers) may require upsizing to meet this limit.

Resistor Color Codes and Component Identification

Through-hole resistors are marked with coloured bands that encode the resistance value and tolerance. A four-band resistor uses the first two bands as significant digits, the third as a multiplier, and the fourth as tolerance. The colour sequence (black=0, brown=1, red=2, orange=3, yellow=4, green=5, blue=6, violet=7, grey=8, white=9) must be memorised or looked up for manual decoding. SMD (surface-mount) resistors use a 3- or 4-digit numerical code: "103" means 10 × 10³ = 10,000 Ω (10 kΩ). LED resistors limit current to the LED's rated forward current (typically 20 mA for standard LEDs): R = (V_supply − V_forward) ÷ I_LED.