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Four-Band Resistor DecoderFree online other calculator — instant results, no sign-up

Decode two significant bands, multiplier and tolerance.

Inputs

Resistance
10 Ω
Tolerance±5%

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About the Four-Band Resistor Decoder

The Four-Band Resistor Decoder reads a resistor’s first two color bands as significant digits, its third band as a multiplier, and its fourth band as tolerance. It converts these selections into nominal resistance in ohms (Ω) and a percentage tolerance. The default Brown, Black, Black, and Gold bands decode to 10 Ω with ±5% tolerance.

First band
Select the first significant digit from Brown (1) through White (9); this digit is dimensionless and defaults to Brown.
Second band
Select the second significant digit from Black (0) through White (9); this digit is dimensionless and defaults to Black.
Multiplier
Select the third-band factor that scales the two-digit value into resistance in ohms (Ω); Black, the default, means ×1.
Tolerance
Select the fourth-band tolerance in percent: Gold (±5%, the default), Silver (±10%), Brown (±1%), or Red (±2%).

Formula and method

R = (10d₁ + d₂) × m Ω; Tolerance = ±t%. For the default bands, d₁ = 1, d₂ = 0, m = 1, and t = 5, so R = (10 × 1 + 0) × 1 Ω = 10 Ω and Tolerance = ±5%.
  • RNominal resistance in ohms (Ω).
  • d₁Dimensionless first significant digit, decoded from the first band.
  • d₂Dimensionless second significant digit, decoded from the second band.
  • mDimensionless multiplier selected by the third band.
  • tTolerance percentage selected by the fourth band, expressed as a percentage number.

Map significant-digit colors to numbers: Black = 0, Brown = 1, Red = 2, Orange = 3, Yellow = 4, Green = 5, Blue = 6, Violet = 7, Gray = 8, and White = 9; Black is not available for the first band. Form the two-digit number as 10d₁ + d₂. For multiplier colors Black through White, use 10 raised to the corresponding color number; Gold means ×0.1 and Silver means ×0.01. Multiply the two-digit number by this factor to obtain resistance in ohms, then look up the tolerance independently from the fourth band.

Worked example

These are the calculator's starting values and the results it actually produces for them.

Inputs

  • First bandBrown
  • Second bandBlack
  • MultiplierBlack
  • ToleranceGold

Results

  • Resistance10 Ω
  • Tolerance±5%

How to use the Four-Band Resistor Decoder

  1. 1Identify the reading direction: the tolerance band is usually separated from the other three by a wider gap and should be read last.
  2. 2Select the First band and Second band colors; the defaults Brown and Black form the significant value 10.
  3. 3Select the Multiplier color; the default Black applies a factor of ×1.
  4. 4Select the Tolerance color; the default Gold specifies ±5%.
  5. 5Read the decoded outputs: with the default selections, Resistance = 10 Ω and Tolerance = ±5%.

Reading your result

The Resistance row gives the nominal, color-coded resistance rather than a measured value; the default result is 10 Ω. The Tolerance row gives the specified percentage deviation above or below that nominal value; the default ±5% means the resistor is specified to fall within 5% of 10 Ω under the applicable reference conditions. Tolerance is relative to resistance, not an absolute value in ohms.

Limitations

This tool assumes a standard four-band resistor with two significant digits, one multiplier band, and one tolerance band. It supports only the listed colors and does not decode five- or six-band markings, missing tolerance bands, or manufacturer-specific codes. Faded colors or an incorrect reading direction can produce an incorrect result. The decoder does not measure resistance or determine power rating, temperature coefficient, condition, or suitability for a circuit.

Common questions

Why is Black available for the second band but not the first?+

Black represents zero. A standard two-significant-digit marking starts with a nonzero digit, while its second digit may be zero, as in the default Brown–Black pair.

Does Gold mean the same thing in the multiplier and tolerance positions?+

No. Gold in the third position means multiply by 0.1, while Gold in the fourth position means ±5% tolerance. Silver similarly means ×0.01 as a multiplier but ±10% as a tolerance.

How do I decide which end of the resistor to read first?+

Look for a wider gap before the tolerance band and place that band last. A Gold or Silver band cannot be a significant digit, which helps establish direction. If spacing or colors are unclear, check the component documentation or confirm the resistance with an appropriate meter.

Why do the default bands give 10 Ω rather than 100 Ω?+

Brown and Black supply the digits 1 and 0, forming 10. The third band is Black, meaning ×1 rather than ×10, so the resistance remains 10 Ω; the final Gold band adds ±5% tolerance without changing the nominal resistance.

Does the calculator save my information?+

Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.

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Results are estimates for informational purposes and are not financial, medical or legal advice.