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Use 4 for common parts, 5 for precision values, or 6 when a temperature-coefficient band is present.
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A temperature difference in kelvin has the same numeric size as a difference in degrees Celsius.
K
Use more digits when documenting precision parts; the color-code result itself is unchanged.
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Bench check

Reading direction

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Meter window

An isolated room-temperature reading from {{ formatResistance(values.lower_ohm) }} through {{ formatResistance(values.upper_ohm) }} agrees with the selected tolerance band.

Temperature estimate

The {{ values.tcr_ppm_per_k }} ppm/K band implies about {{ formatResistance(values.drift_ohm) }} of first-order drift across {{ computation.normalizedInputs.temperature_delta_c }} K.

Before replacement

Color bands do not encode power rating, voltage rating, resistor technology, aging, self-heating, or circuit loading. Isolate doubtful parts and compare the measurement with the schematic or datasheet.

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Color bands let a small axial resistor carry its nominal resistance and tolerance without printed digits. The bands are read as a short number followed by a multiplier. A separate tolerance band states how far a new part may vary from that nominal value.

Reading direction matters because the same colors in reverse order can describe a different resistance. The tolerance band is commonly separated by a wider gap near one end. If the first apparent significant band is black, rotate the part and inspect the spacing again before accepting the decode.

Layout Value bands Final information Typical reason to use it
4 bands 2 digits and multiplier Tolerance Common general-purpose parts
5 bands 3 digits and multiplier Tolerance Values that need another significant digit
6 bands 3 digits and multiplier Tolerance and temperature coefficient Parts whose resistance drift with temperature must be estimated

The code identifies resistance, tolerance, and sometimes temperature coefficient of resistance (TCR). It does not reveal power rating, maximum voltage, construction, pulse capability, aging, or damage. A bench measurement and the component datasheet remain necessary when those properties affect a repair or design.

How to Use This Tool:

Start with the physical band count and reading direction, then enter the colors in order.

  1. Choose the band count that matches the part. Four bands use two significant digits, while five and six bands use three.
  2. Select each band color from the end opposite the separated tolerance or TCR bands. The resistor drawing and summary update with every choice.
  3. Review the nominal value and tolerance window. For a six-band part, enter a temperature change from 0 to 100 K to estimate first-order drift from the TCR band.

Interpreting Results:

  • Nominal resistance is the coded target value, not a guaranteed meter reading.
  • Lower and upper limits are the inclusive tolerance window around nominal resistance.
  • Review orientation means the first significant digit is black, an unusual reading that should be checked against the wider end gap.
  • Temperature drift is a linear first-order estimate for the entered temperature difference, not a full temperature curve.

Technical Details:

Significant-digit colors form an integer. The multiplier color scales that integer in ohms, the tolerance color creates a symmetric range, and a sixth TCR band estimates the change caused by a temperature difference.

Formula Core:

The three calculations below produce nominal resistance, its tolerance limits, and optional first-order temperature drift.

R =S×M Rlow,Rhigh =R×(1−t100),R×(1+t100) ΔRT ≈R×α×ΔT÷106
  • S is the two- or three-digit number formed by the significant bands.
  • M is the multiplier, so R is measured in ohms.
  • t is tolerance in percent; both endpoints belong to the allowed window.
  • α is TCR in parts per million per kelvin (ppm/K), and ΔT is the temperature difference in kelvin. A temperature difference in kelvin has the same numeric size as one in degrees Celsius.

Lookup and Rule Core:

Only colors valid for a band's role can be selected. A dash means that color has no supported value for that role.

Color Digit Multiplier Tolerance TCR
Black01——
Brown110±1%100 ppm/K
Red2100±2%50 ppm/K
Orange31,000—15 ppm/K
Yellow410,000—25 ppm/K
Green5100,000±0.5%—
Blue61,000,000±0.25%10 ppm/K
Violet710,000,000±0.1%5 ppm/K
Gray8100,000,000±0.05%—
White91,000,000,000——
Gold—0.1±5%—
Silver—0.01±10%—

Display precision changes visible rounding from two to five significant digits. The underlying resistance, tolerance limits, and drift calculation are not rounded before display.

Accuracy Notes:

Color identification can be affected by lighting, fading, coatings, and nearby bands. The supported lookup also excludes markings outside the selectable 4-, 5-, and 6-band scheme, including newer or manufacturer-specific colors and interrupted-band conventions.

  • Measure resistance only with the circuit safely de-energized, and isolate a lead when parallel circuit paths could change the reading.
  • A meter value inside the tolerance window supports the selected code but does not prove the part's power or voltage rating.
  • The TCR estimate assumes a constant coefficient across the entered 0 to 100 K difference and ignores self-heating and nonlinear datasheet curves.

Worked Examples:

Six-band 4.7 kΩ part

Yellow, violet, and black form 470; brown multiplies by 10, giving 4,700 Ω. Brown tolerance gives an inclusive 4,653 to 4,747 Ω window. A red TCR band is 50 ppm/K, so a 25 K temperature difference produces a first-order drift estimate of 5.875 Ω.

References: