Pick the band colours on a 4-band or 5-band resistor to read its resistance, tolerance and minimum to maximum range.
Resistor colour bands encode the resistance value: the first bands give the significant digits, the next band is the multiplier (the power of ten to multiply by, with gold and silver as fractional multipliers), and the final band gives the tolerance. A 4-band resistor uses two digit bands; a 5-band resistor uses three, giving a more precise value. The result is formatted in ohms, kilohms or megohms as appropriate, and the minimum and maximum values apply the tolerance percentage to the nominal resistance. Band colours follow the standard code, including violet for the digit 7.
How is a 4-band resistor read? The first two bands are digits, the third is the multiplier and the fourth is the tolerance. For example red, violet, brown and gold means 2, 7, times 10, with 5 percent tolerance: 270 ohms plus or minus 5 percent.
What does no tolerance band mean? A resistor with no tolerance band has a tolerance of 20 percent, the widest standard grade. Gold means 5 percent and silver means 10 percent.