Electronics
Resistor Color Code Calculator
Decode 4, 5 and 6-band resistor colour codes into resistance, tolerance and the guaranteed range.
R = digits × 10^multiplier, ± tolerance
Also called resistor colour code · 4 band resistor
Science · 11 calculators
Electronics Calculators
Resistor colour codes, LED resistors, voltage dividers, capacitors, RC time constants, reactance, impedance and battery life.
Electronics
LED Resistor Calculator
Series resistor value and wattage for an LED from supply voltage, forward voltage and current.
R = (V_supply − V_forward) / I_forward
Also called led series resistor · current limiting resistor
Electronics
Voltage Divider Calculator
Output voltage of a two-resistor divider, the current it draws, and R2 for a target output.
V_out = V_in × R₂ / (R₁ + R₂)
Also called potential divider · resistor divider
Electronics
Capacitor Calculator
Capacitor charge and energy stored from capacitance and voltage, in several unit scales.
Q = C × V
Also called capacitance calculator · capacitor energy
Electronics
Capacitors in Series Calculator
Total capacitance of capacitors in series and the voltage each one sees.
1/C_total = 1/C₁ + 1/C₂ + …
Also called series capacitance · capacitors in series formula
Electronics
Capacitors in Parallel Calculator
Total capacitance of capacitors in parallel — the values simply add together.
C_total = C₁ + C₂ + C₃ + …
Also called parallel capacitance · capacitors in parallel formula
Electronics
RC Time Constant Calculator
RC time constant, charge and discharge times, and the filter cut-off frequency.
τ = R × C
Also called rc circuit calculator · tau calculator
Electronics
Frequency Calculator
Frequency from period or from wave speed and wavelength — in hertz, with the period in seconds.
f = 1 / T
Also called frequency formula · f = 1/t
Electronics
Reactance Calculator
Capacitive and inductive reactance at a given frequency, and the resonant frequency of an LC pair.
Xc = 1 / 2πfC
Also called capacitive reactance · inductive reactance
Electronics
Impedance Calculator
Total impedance of a series RLC circuit, with the phase angle and power factor.
Z = √(R² + (Xl − Xc)²)
Also called rlc impedance · z calculator
Electronics
Battery Life Calculator
How long a battery lasts from its capacity and the load current, with a usable-capacity allowance.
Runtime = capacity × usable fraction ÷ lo…
Also called battery runtime · how long will battery last
Key electronics formulas
| Resistor Color Code | R = digits × 10^multiplier, ± tolerance |
|---|---|
| LED Resistor | R = (V_supply − V_forward) / I_forward |
| Voltage Divider | V_out = V_in × R₂ / (R₁ + R₂) |
| Capacitor | Q = C × V · E = ½CV² |
| Capacitors in Series | 1/C_total = 1/C₁ + 1/C₂ + … |
| Capacitors in Parallel | C_total = C₁ + C₂ + C₃ + … |
| RC Time Constant | τ = R × C · V(t) = V₀(1 − e^(−t/τ)) · f_c = 1 / 2πRC |
| Frequency | f = 1 / T |
| Reactance | Xc = 1 / 2πfC · Xl = 2πfL · f₀ = 1 / 2π√(LC) |
| Impedance | Z = √(R² + (Xl − Xc)²) · φ = arctan((Xl − Xc)/R) |
Electronics questions
Which end do I read from?
Start from the band closest to one end. The tolerance band (often gold or silver) is usually spaced slightly further away and comes last.