Resistor color code calculator: read color bands into resistance, tolerance, and value ranges for 4, 5, or 6 band resistors. Free, runs locally, no signup.
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Worked example: decoding 4700 ohms by hand
Take the common yellow-violet-red-gold band set. Band 1 is yellow, which maps to digit 4. Band 2 is violet, digit 7. The first two digits combine as b1 x 10 + b2, so 4 x 10 + 7 = 47. The multiplier band is red, index 2, meaning 10 to the power 2 = 100. Multiply: 47 x 100 = 4700 ohms, shown as 4.7 k-ohm.
The gold tolerance band is index 2 in the tolerance list, which is 5 percent. The low end is 4700 x 0.95 = 4465 ohms and the high end is 4700 x 1.05 = 4935 ohms, displayed as 4.465 k-ohm to 4.935 k-ohm. Check the arithmetic by hand when a build matters: a real 4.7 k resistor that measures 4.6 k is inside spec, not a faulty part.
Swap red for yellow on the multiplier and the same first two digits give 47 x 10,000 = 470,000 ohms, or 470 k. One band color shifts the value by a factor of 10, which is why reading order matters: tolerance band, usually gold or silver, sits at the far end so you know where to start.
What this 4-band model does not cover
The multiplier select only runs black through white, indexes 0 to 9, so it handles multipliers of 1 to 1,000,000,000. It cannot express the gold x 0.1 or silver x 0.01 multipliers found on sub-1-ohm resistors, such as a 0.5 ohm current-sense part. A 5-band precision resistor with a third significant digit, for example red-red-black-black-brown = 2200 ohms at 1 percent, must be decoded by entering only its first two digits and adjusting, since this tool has no third-digit band.
Tolerance ranges are also optimistic in practice. The 5 percent figure assumes a 25 C measurement; resistance drifts with temperature, typically 100 to 250 ppm per degree C for standard film types. A 4.7 k resistor 60 degrees above room temperature can shift by roughly 4700 x 0.00025 x 60 = about 70 ohms, adding to the tolerance band. For circuits where that matters, measure the part at operating temperature rather than trusting the printed bands alone.
Zero-ohm jumpers are a real edge case: a single black band reads as 0 ohms here, which is technically correct, but real zero-ohm links are rated by current capacity, usually 1 to 3 amps, not resistance.
