🔋 Electronics calculators
Free online electronics calculators for hobbyists, students and circuit designers. Find the right LED resistor, design a voltage divider, read a resistor colour code, set a 555 timer frequency, choose an RC filter cut-off, size a buck or boost converter and check PCB trace width — each with formulas, standard values and design tips.
30 free calculators · no sign-up · works on mobile
Resistors & basic circuitsCapacitors, inductors & ACTiming, amplifiers & signalsPower electronics & PCBSensors
Most popular electronics calculators
Resistors & basic circuits
- LED Resistor CalculatorCalculate the series resistor value and wattage for one LED or a string of LEDs from supply voltage, forward voltage and current.
- Voltage Divider CalculatorCalculate the output voltage of a resistor voltage divider, or the resistor values needed for a target output — with divider current and power.
- Current Divider CalculatorCalculate how a total current splits between two parallel resistors using the current divider rule — with branch currents and equivalent resistance.
- Resistor Color Code Calculator (4-Band)Find a resistor's value and tolerance from its 4 colour bands — or look up the colours for any resistance. Includes the full colour chart.
- Zener Diode Resistor Calculator (Voltage Regulator)Calculate the series resistor and power ratings for a Zener diode shunt regulator from input voltage, Zener voltage and load current.
- Transistor Base Resistor Calculator (BJT Switch)Calculate the base resistor for an NPN or PNP transistor used as a switch — from load current, hFE and drive voltage, with overdrive for saturation.
- Wheatstone Bridge CalculatorCalculate the output voltage of a Wheatstone bridge, or the unknown resistance at balance — for strain gauges, RTDs and sensor circuits.
Capacitors, inductors & AC
- Capacitor Energy and Charge CalculatorCalculate the energy stored in a capacitor and its charge from capacitance and voltage — for supercapacitors, DC links and flash circuits.
- Capacitors in Series and Parallel CalculatorCalculate the total capacitance of up to four capacitors in series or parallel, with the total voltage rating guide and charge.
- Inductor Energy CalculatorCalculate the energy stored in an inductor's magnetic field from inductance and current with E = ½LI² — for chokes, relays and SMPS design.
- RL Time Constant CalculatorCalculate the time constant τ = L/R of an inductor-resistor circuit, plus current rise and decay at any time — for relays, solenoids and filters.
- Reactance and Impedance Calculator (XL, XC and Z)Calculate inductive reactance, capacitive reactance and series RLC impedance at any frequency — with phase angle.
- LC Resonant Frequency CalculatorCalculate the resonant frequency of an LC circuit — or the inductance or capacitance needed to tune to a frequency — for filters, oscillators and radios.
- RC Filter Cutoff Frequency CalculatorCalculate the −3 dB cutoff frequency of an RC low-pass or high-pass filter, or the R or C needed for a target cutoff — with attenuation at any frequency.
- Electrolytic Capacitor Life Calculator (10 °C Rule)Estimate the expected life of an aluminium electrolytic capacitor at your operating temperature from its rated hours and temperature, using the 10-degree rule.
Timing, amplifiers & signals
- 555 Timer Calculator (Astable Mode)Calculate the frequency, duty cycle, high time and low time of a 555 timer in astable mode from R1, R2 and C — or choose parts for a target frequency.
- Op-Amp Gain Calculator (Inverting and Non-Inverting)Calculate the voltage gain and output of an inverting or non-inverting op-amp amplifier from Rf and Rin — or the resistor needed for a target gain.
- Instrumentation Amplifier Gain Calculator (Rg)Calculate the gain-setting resistor Rg for INA128, INA333, AD620 and other instrumentation amplifiers — or the gain from a given Rg.
- PWM Duty Cycle CalculatorCalculate PWM duty cycle, period, on-time and average output voltage from frequency and pulse width — for motor speed control, LEDs and microcontrollers.
- ADC Resolution Calculator (LSB and Step Size)Calculate ADC step size (LSB), number of levels and the digital code for an input voltage from bit depth and reference voltage — including 4–20 mA PLC inputs.
- Signal-to-Noise Ratio (SNR) CalculatorCalculate signal-to-noise ratio in dB from signal and noise voltages or powers — with ENOB (effective number of bits) for ADCs.
- dBm to Watts Converter (and Watts to dBm)Convert dBm to watts, milliwatts and dBW and back — with voltage across 50 Ω — for RF, Wi-Fi, radio and fibre power levels.
Power electronics & PCB
- Buck Converter Calculator (Inductor and Capacitor)Calculate duty cycle, inductor value, ripple current and output capacitor for a buck (step-down) DC-DC converter.
- Boost Converter Calculator (Inductor and Capacitor)Calculate duty cycle, input current, inductor value and output capacitor for a boost (step-up) DC-DC converter.
- MOSFET Power Dissipation Calculator (Conduction and Switching Loss)Estimate MOSFET conduction and switching losses from Rds(on), current, voltage, switching frequency and rise/fall times — and the junction temperature.
- Heat Sink Calculator (Thermal Resistance)Calculate the maximum heat sink thermal resistance for a transistor, MOSFET or regulator from power dissipation, junction and ambient temperatures.
- PCB Trace Width Calculator (IPC-2221)Calculate the PCB trace width needed for a current and temperature rise using the IPC-2221 formula — for external and internal layers and copper weights.
- Battery Charging Time CalculatorCalculate how long a battery takes to charge from its capacity, charging current, starting charge level and charging efficiency — lead-acid or lithium.
Sensors
- NTC Thermistor Calculator (Beta Equation)Calculate NTC thermistor resistance at any temperature, or temperature from resistance, using the beta (B) equation — for 10k, 100k and other thermistors.
- Strain Gauge Calculator (ΔR and Bridge Output)Calculate the resistance change and Wheatstone bridge output of a strain gauge from gauge factor, strain and excitation — for quarter, half and full bridges.
Design faster, with fewer mistakes
Each calculator works in both directions: get the output of a circuit, or enter the output you want and solve for the component value. Results are shown in convenient units — kΩ, µF, mH, kHz — and pages list the nearest standard values.
Learn as you calculate
Every page explains the formula, gives a worked example and includes reference tables, so the calculators double as a quick electronics reference.
Frequently asked questions
What resistor do I need for an LED?
R = (supply voltage − LED forward voltage) ÷ LED current. The LED resistor calculator does this for single LEDs and series strings.
Can I solve for a component value?
Yes. Enter the result you want, then press × on the component field to have it calculated.
Are standard E12/E24 values included?
Pages such as the LED resistor and resistor colour code calculators list standard values to help you pick real parts.
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