Electrical Engineering Calculators
20 tools in this collection — free, instant, and private in your browser.
Electrical engineering calculators take the repetitive arithmetic out of circuit analysis, component selection, and power calculations. They are designed for electronics hobbyists, engineering students, technicians, and makers who need reliable numbers fast without reaching for a dedicated circuit simulator.
At the foundation sits the Ohm's Law Calculator, which solves for voltage, current, or resistance given the other two. The Electronics Power Wheel expands this to all four quantities (V, I, R, P) and lets you enter any two to find the remaining pair. For resistor networks, the Parallel Resistance Calculator and Resistors in Parallel Calculator handle multi-branch circuits, while the Voltage Divider Calculator is the go-to tool for biasing and signal-scaling designs.
Energy storage components have their own dedicated tools. The Capacitor Energy Calculator (E = ½CV²) and Inductor Energy Calculator (E = ½LI²) quantify stored energy in a circuit. For timing and filtering applications, the RC Time Constant Calculator gives the characteristic charge and discharge period, while the LC Resonant Frequency Calculator pinpoints the natural oscillation frequency of an inductor-capacitor tank circuit.
Component-specific tools cover common practical needs. The LED Series Resistor Calculator prevents LEDs from burning out by sizing the current-limiting resistor. The Resistor Color Code Calculator decodes or encodes the colored bands on a resistor. The 555 Timer Astable Mode Calculator handles the popular NE555 oscillator configuration by computing frequency and duty cycle from resistor and capacitor values.
Power and loss tools round out the set. The Power Dissipation Calculator, Power Triangle Calculator, Voltage Drop Calculator, Battery Life Calculator, and Watts to dBm Converter are indispensable for sizing conductors, estimating battery runtimes, and working with RF power levels. Pick the tool that corresponds to the unknown you need to find, fill in your known values, and verify units before comparing results with measured readings.
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| Tool | What it does |
|---|---|
| 555 Timer Astable Mode Calculator | Calculate the frequency, period and duty cycle of a 555 timer in astable (free-running oscillator) mode. Enter R1, R2 in kΩ and C in µF. |
| Battery Life Calculator | Calculate how long a battery will last. Enter battery capacity in mAh, average load current in mA and a derating efficiency to get hours and days. |
| Capacitor Energy Calculator (E = ½CV²) | Calculate the energy stored in a capacitor and its charge. Enter capacitance in µF and voltage to get energy in joules and millijoules, plus charge in coulombs. |
| Capacitors in Series Calculator | Calculate the equivalent capacitance of up to 4 capacitors wired in series. Input values in nanofarads (nF). Also shows the parallel equivalent. |
| Electronics Power Wheel (V, I, R, P) | Solve for any one of voltage (V), current (I), resistance (R) or power (P) using Ohm's Law and power formulas P=VI=I²R=V²/R. Enter any two to find the rest. |
| Inductor Energy Calculator (E = ½LI²) | Calculate the energy stored in an inductor's magnetic field. Enter inductance in mH and current in amps to get energy in joules and millijoules. |
| LC Resonant Frequency Calculator | Calculate the resonant frequency of an LC circuit (tank circuit). Enter inductance (mH) and capacitance (µF) to find frequency and characteristic impedance. |
| LED Series Resistor Calculator | Calculate the correct series resistor for an LED. Enter supply voltage, LED forward voltage and desired current to get resistance in ohms and power dissipation. |
| Ohm's Law Calculator | Calculate voltage, current, resistance and power using Ohm's Law (V = IR). Enter any two values to find the other two instantly. |
| Parallel Resistance Calculator | Calculate the equivalent resistance of 2 to 4 resistors in parallel. Uses 1/Rp = 1/R1 + 1/R2 + … Enter R3 and R4 as 0 to ignore them. |
| Power Dissipation Calculator | Calculate power dissipated as heat in a resistor or component. Enter voltage, current and resistance (any two), plus thermal resistance (θ_JA) to estimate temperature rise. |
| Power Triangle Calculator (P, V, I, R) | Calculate any two unknowns from the power triangle: P=VI, V=IR, P=I²R, P=V²/R. Select which two values you know and the calculator finds the rest. |
| RC Time Constant Calculator (τ = RC) | Calculate the RC time constant τ = RC, the corner frequency of an RC filter, and the time to full charge (5τ). Enter resistance in ohms and capacitance in µF. |
| Resistor Color Code Calculator | Decode 3-band, 4-band or 5-band resistor colour codes to ohms and tolerance. Select the number of bands and each colour to get the resistance instantly. |
| Resistors in Parallel Calculator | Calculate the equivalent resistance of up to 4 resistors wired in parallel using 1/R = 1/R₁ + 1/R₂ + … Also shows the series equivalent for comparison. |
| Voltage Divider Calculator | Calculate the output voltage of a resistor voltage divider. Enter Vin, R1 and R2 to find Vout, division ratio and current through the divider. |
| Voltage Drop Calculator | Calculate voltage drop through copper wire. Enter AWG gauge, one-way wire length in metres and current in amps to find drop, total resistance and power loss. |
| Watts to dBm Converter | Convert RF power from watts to dBm and dBW. Enter power in watts to get dBm and dBW. Used in RF engineering, cellular and Wi-Fi design. |
| Wire Gauge Ampacity Calculator (AWG) | Find the ampacity (current-carrying capacity) and resistance of copper wire by AWG gauge. Covers AWG 28 (thin signal wire) to AWG 0000 (heavy power cable). |
| dBm to Watts Converter | Convert RF power from dBm to watts and milliwatts. Enter dBm to get power in W, mW and dBW. Used in RF engineering, Wi-Fi, and telecommunications. |
Frequently asked questions
- What is the difference between the Parallel Resistance Calculator and the Resistors in Parallel Calculator?
- Both tools compute the equivalent resistance of parallel branches. The Parallel Resistance Calculator is optimised for two-resistor combinations with a quick formula, while the Resistors in Parallel Calculator lets you add an arbitrary number of resistors to the parallel network.
- How does the RC Time Constant Calculator help with filter design?
- The RC time constant (tau = R x C) determines the cutoff frequency of a simple first-order RC low-pass or high-pass filter. The calculator shows tau and the corresponding 3 dB frequency, letting you choose component values to hit a target cutoff without manual computation.
- Can I use the Battery Life Calculator for rechargeable lithium cells?
- Yes. Enter the battery capacity in milliamp-hours and the average current draw of your circuit. The calculator returns the estimated runtime. For lithium cells, consider applying an efficiency factor of around 80 to 90 percent to account for voltage sag and incomplete discharge cycles.