Resistors, Capacitors and Filters

These calculators size the passive parts of a circuit. Read a resistor from its bands, combine resistors or capacitors, set a divider or LED resistor, and find the time constant, cutoff frequency or 555 timer frequency from the component values.

Tools in this group

• 555 Timer Calculator — Enter R1, R2 and C to get the 555 astable frequency and duty cycle, or R and C for the monostable pulse width.
• Capacitor Code Calculator — Type the code printed on a capacitor to get its value in pF, nF and µF, or find the code for a value.
• Capacitors in Series and Parallel Calculator — List your capacitor values to get the total capacitance in series and parallel, how a DC voltage divides and the energy stored.
• LED Resistor Calculator — Enter the supply voltage, LED forward voltage and current to get the resistor value, the nearest standard value and its power rating.
• Low Pass Filter Calculator — Enter the components to get the cutoff frequency, or a target frequency to get the component, with the response drawn on a Bode plot.
• Parallel Resistor Calculator — List your resistor values to get the total resistance in parallel and in series, the current in each, and a standard pair for a target.
• RC Time Constant Calculator — Enter the resistor and capacitor to get the time constant, the charge curve and how long the capacitor takes to reach a voltage.
• Resistor Color Code Calculator — Pick the colour of each band to read the resistance and tolerance, or type a value to see its colour bands.
• Voltage Divider Formula and Calculator — Enter the input voltage and two resistors to get the output, or solve for a resistor, with load, current and standard values.