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Decode resistor colour bands.
Resistors use coloured bands to encode their resistance and tolerance. This calculator decodes 4-band and 5-band resistors: choose the colour of each band and it computes the resistance in ohms and the tolerance range.
It is handy when a resistor's value is not printed numerically, or to check a component before soldering it into a circuit.
Colour → digit: black 0, brown 1, red 2, orange 3, yellow 4, green 5, blue 6, violet 7, grey 8, white 9. The multiplier band is 10 raised to that digit.
Start from the band closest to a lead — the digit bands are grouped at one end and the tolerance band is set slightly apart at the other. If unsure, the gold or silver band is almost always the tolerance and goes last.
A 4-band resistor uses two significant digits plus a multiplier and tolerance. A 5-band resistor adds a third significant digit for greater precision, common in 1% and better resistors.
As a multiplier, gold means ×0.1 and silver means ×0.01, which produce sub-ohm resistances. As the final band they instead mean ±5% and ±10% tolerance.
The tolerance band gives the guaranteed range. A 1 kΩ ±5% resistor can measure anywhere from 950 Ω to 1050 Ω and still be in spec, which is why the calculator shows the min and max.