Tech & Engineering

Electronics & Engineering Calculators

Ohm's law, resistors, capacitors, power and signals. Free calculators with formulas and worked examples.

Basic circuits

Ohm's Law CalculatorPick the two values you know and get the other two.Electrical Power Calculator (Single and Three Phase)Work out watts, kVA and kvar from volts, amps and power factor.Resistors in Series and Parallel CalculatorCombine up to four resistors. Leave unused values at 0.Capacitors in Series and Parallel CalculatorCombine up to four capacitors. Leave unused values at 0.Voltage Divider CalculatorFind the output of a resistor divider from the input voltage and R1 and R2.LED Resistor CalculatorPick a resistor that sets the right current through an LED.Resistor Color Code CalculatorChoose the colours of the four bands to read the value.

Filters and timing

RC Time Constant CalculatorFind how fast a capacitor charges through a resistor.RC Low-Pass Filter Cutoff CalculatorFind the −3 dB frequency of an RC filter.LC Resonant Frequency CalculatorFind the frequency at which an inductor and capacitor resonate.555 Timer Astable CalculatorDesign a 555 oscillator from component values.

Wiring

AWG Wire Gauge CalculatorConvert an American Wire Gauge number to millimetres and ohms per kilometre.Voltage Drop CalculatorCheck whether a cable run is too long for the current it carries.Wire Resistance CalculatorHow much resistance does a length of wire add to your circuit?

Power and energy

Battery Life CalculatorWork out battery runtime from capacity and current draw.UPS and Battery Backup Runtime CalculatorHow long will a battery bank run your load?Transformer Turns Ratio CalculatorFind the secondary side of an ideal transformer from the primary values.

Signals

Decibel (dB) CalculatorConvert between ratios and decibels for power and voltage (amplitude).Frequency and Wavelength CalculatorFind the wavelength for a frequency, or the frequency for a wavelength.Shannon Channel Capacity CalculatorWhat is the theoretical maximum data rate of a channel?

Mechanical

Torque, Power and RPM CalculatorFind mechanical power from torque and speed.Gear Ratio CalculatorWork out what a pair of gears does to speed and torque.

Batteries

Battery Pack CalculatorPlan an NxM pack from individual cells.Amp Hours to Watt Hours Calculator (and the 100 Wh Airline Limit)Enter the capacity and the battery voltage.

Components

Capacitor Energy Calculator (Joules and Charge)Enter the capacitance and voltage.Zener Diode Resistor CalculatorEnter the supply voltage, Zener voltage and the load current.Capacitor Code Calculator (104 to nF)Enter the three-digit code from the capacitor.

AC circuits

Reactance Calculator (Capacitive and Inductive)Enter the frequency, capacitance and inductance.RLC Impedance Calculator (Series Circuit)Enter the resistance, inductance, capacitance, frequency and supply voltage.

Circuit design

PCB Trace Width Calculator (IPC-2221)Enter the current, allowed temperature rise and copper weight.Op-Amp Gain Calculator (Inverting and Non-Inverting)Choose the configuration and enter the resistors and input voltage.ADC Resolution Calculator (LSB, SNR, Output Code)Enter the number of bits, the reference voltage and an input voltage.

Power electronics

Linear Regulator Power Dissipation CalculatorEnter the input and output voltages, the load current and the thermal resistance.kVA to kW Calculator (Power Factor and Current)Enter the kVA rating, power factor and supply voltage.

Radio

Dipole Antenna Length CalculatorEnter the frequency and the shortening factor.

About these calculators

Everyday circuit and engineering calculations for students, hobbyists and technicians. Values use SI units, and each page lists the formula and the assumptions, such as ideal components.

Each calculator explains its formula, includes a worked example and lists its sources. Read how we check them on our editorial policy page, or browse all calculators.

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Please note: TheCalcTools gives general estimates for information and education. It is not financial, medical, legal or tax advice, and results should be checked before you make a decision. See our disclaimer and about page.