Resistors & Capacitors

Decode a resistor's color bands, work out an RC time constant and cutoff, read a capacitor code, and snap to a standard value.

Resistor color code

Pick the band count and each band's color. The body shows what the part looks like.

Bands

RC time constant

Time constant τ = R × C, and the −3 dB cutoff f = 1 ÷ (2πRC). A capacitor charges to about 63% in one τ and is within 1% after about 5τ.

Resistance

Capacitance

Capacitor code

Three-digit ceramic codes: the first two digits are significant, the third is the number of zeros, and the result is in picofarads (so 104 = 10 then four zeros = 100 000 pF = 100 nF). An R marks a decimal point (4R7 = 4.7 pF).

Code

Value

Standard values

Preferred resistor values (each times a power of ten). E24 is the 5% series; E12 (bold) is the 10% subset.

Series	Values (×10ⁿ)

Color code table

Color	Digit	Multiplier	Tolerance	Temp. co.