// free tools for electronics hobbyists

Stop guessing.
Do the math.

Fast, accurate calculators for resistors, LEDs, filters, timers, and more.

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Fundamentals

Ohm's Law

Solve for voltage, current, resistance, or power. Enter any two values.

LED Resistor

Find the right current-limiting resistor for your LED. Don't fry it.

Color Code

Decode bands to value or find the bands for any resistance. 4- and 5-band supported.

Voltage Divider

Calculate output voltage, or find R1/R2 values for a target output.

Series / Parallel

Combine resistors or capacitors in series or parallel. Add as many as you need.

Analog

555 Timer

Astable and monostable modes. Frequency, period, duty cycle.

RC / Filter

Time constant τ, cutoff frequency, and charge/discharge curves.

Cap Charge

Voltage vs time during RC charge or discharge.

Battery Life

Estimate runtime from capacity and load current. Includes Peukert correction.

Wire Gauge

AWG to resistance and current capacity. Pick the right wire.

Active

BJT Bias

Q-point, base/collector/emitter voltages for common-emitter stage.

Op-Amp Gain

Inverting and non-inverting configurations. Gain and resistor values.

LDO / 78xx

LM78xx series dropout, heat dissipation, and capacitor selection.

Zener

Series resistor sizing for zener shunt regulator circuits.

Power & Signal

dB Converter

Convert between dB, voltage ratio, and power ratio.

PWM Voltage

Average output voltage from duty cycle and supply.

Filter Cap

Minimum filter capacitor for target ripple voltage.

Transformer

Turns ratio, secondary voltage, and VA rating.

Digital / MCU

I²C Pull-Up

Optimal pull-up resistor for I²C bus speed and capacitance.

GPIO Budget

Total current draw across GPIO pins for Arduino / RPi.

Debounce RC

R and C values to debounce a mechanical switch input.

RF & Advanced

LC Resonance

Resonant frequency of an LC tank circuit.

Antenna

Dipole and quarter-wave antenna length for a given frequency.

Reference

SMD Code

Decode 3-digit and 4-digit SMD resistor markings.

Cap Code

Decode 3-digit ceramic capacitor codes to picofarads.

Unit Converter

Convert between mA/A, mV/V, pF/nF/µF, and more.