Resistor Calculator
Turn the colour bands on a through-hole resistor into its value in ohms, with the tolerance range. Yellow-violet-red-gold reads 4.7 kΩ ±5%.
Electronics & Physics
18 tools
Tools in this category
Voltage Divider Calculator
Find the output voltage of a two-resistor divider from Vin, R1 and R2, with divider current, resistor power and the sag caused by a resistive load.
Resistance Calculator
Find resistance in ohms from any two of voltage, current and power, with conductance and dissipated power. 120 V and 60 W gives 240 Ω.
Schmitt Trigger Calculator
Find the upper and lower switching thresholds and hysteresis width of an inverting or non-inverting op-amp Schmitt trigger from R1, R2, Vref and output levels.
LC Tank Calculator
Find the resonant frequency of an inductor and capacitor, or the L or C needed for a target frequency. 100 µH with 100 pF resonates at 1.592 MHz.
Comparator Calculator
Find the upper and lower switching thresholds and hysteresis width of an inverting comparator with positive feedback from Vref, R1, R2 and output levels.
Series Parallel Combined
Finds the equivalent resistance of three resistors wired R1 + (R2 ∥ R3) or (R1 + R2) ∥ R3, with optional supply current and power from Ohm's law.
LC Resonance Calculator
Find the resonant frequency of an inductor and capacitor pair from L and C in H to nH and F to pF, plus angular frequency, period and reactance at resonance.
LED Current Limiting
Find the series resistor for one LED or a string: exact ohms from supply and forward voltage, the next E12 value, real current and resistor wattage.
LC Filter Calculator
Find the cutoff frequency of a second-order LC low-pass or high-pass filter from L and C, plus the characteristic impedance √(L/C) it should drive.
Band Pass Filter Calculator
Find the lower and upper cutoff, centre frequency, bandwidth and Q of a passive RC band-pass filter from R1, C1, R2 and C2, with each step of the working shown.
LED Array Calculator
Plan an LED array: how many LEDs fit in series per string, how many parallel strings you need, the resistor value and its wattage for each string.
Low Pass Filter Calculator
Find the −3 dB cutoff frequency of a first-order RC or RL low-pass filter, plus the time constant and the gain and phase at any signal frequency.
Power Factor Calculator
Find power factor from real and apparent power or from watts, volts and amps on single- or three-phase supplies, with phase angle and kVAR.
Power Factor Correction
Sizes the capacitor bank to lift a load's power factor: kvar from P × (tan φ1 − tan φ2), capacitance in µF, and the drop in kVA and line current.
Power Calculator (Electrical)
Find electrical power in watts from any two of voltage, current and resistance using P = VI, I²R or V²/R, with the missing third value filled in.
Transformer Efficiency
Find transformer efficiency from output power plus core and copper losses, or from measured input and output. 80 kW with 2.5 kW of losses gives 96.97%.
Transformer Power Rating
Size a transformer in kVA from voltage and load current, single or three phase, add spare capacity and get the next standard ANSI size and its full-load amps.