The temperature coefficient of resistance, or TCR, describes how much a resistor value changes as temperature changes. It is commonly written in parts per million per kelvin (ppm/K) and appears as a sixth color band on some precision resistors. Decode the nominal bands first with the Resistor Color Code Calculator, then treat the final band as a stability specification rather than another multiplier.
What ppm/K means
A TCR of 100 ppm/K means a fractional change of 100 parts per million for each kelvin of temperature change, subject to the part specification and sign convention. For a 10 kohm resistor, 100 ppm/K corresponds to about 1 ohm per kelvin in a simple first-order calculation. The nominal value is still 10 kohm; TCR describes drift around it.
Common TCR color reference
| Band color | TCR | Approximate change per 10 kohm and 1 K |
|---|---|---|
| Black | 250 ppm/K | 2.5 ohms |
| Brown | 100 ppm/K | 1 ohm |
| Red | 50 ppm/K | 0.5 ohm |
| Orange | 15 ppm/K | 0.15 ohm |
| Yellow | 25 ppm/K | 0.25 ohm |
| Green | 20 ppm/K | 0.2 ohm |
| Blue | 10 ppm/K | 0.1 ohm |
| Violet | 5 ppm/K | 0.05 ohm |
| Grey | 1 ppm/K | 0.01 ohm |
These are the common reference values used by this calculator. Confirm the exact mapping, sign, reference temperature, and test conditions against the resistor series datasheet.
Where the TCR band sits
In a six-band marking, count three significant digits, then multiplier, tolerance, and temperature coefficient. The tolerance band is normally separated from the first group; the TCR band is the last visible information. Brown, red, orange, yellow, blue, and violet can represent different ppm/K values in common charts, but a manufacturer-specific mark can override the generic color convention.
Calculate temperature drift
Use change in resistance ~= nominal resistance x TCR x temperature change / 1,000,000. Suppose a six-band resistor decodes to 10 kohm, +/- 1 percent, 50 ppm/K. A 20 K temperature change gives 10,000 x 50 x 20 / 1,000,000 = 10 ohms, or about 0.1 percent. That is separate from the initial +/- 1 percent tolerance. The sign and actual curve may differ from this first-order estimate.
Worked TCR examples
| Nominal value | TCR | Temperature change | Approximate drift |
|---|---|---|---|
| 1 kohm | 100 ppm/K | 10 K | 1 ohm |
| 1 kohm | 50 ppm/K | 40 K | 2 ohms |
| 10 kohm | 100 ppm/K | 20 K | 20 ohms |
| 10 kohm | 50 ppm/K | 20 K | 10 ohms |
| 10 kohm | 10 ppm/K | 50 K | 5 ohms |
| 100 kohm | 20 ppm/K | 25 K | 50 ohms |
| 4.7 kohm | 5 ppm/K | 50 K | 1.175 ohms |
| 220 ohms | 250 ppm/K | 30 K | 1.65 ohms |
When TCR matters
Temperature coefficient matters in reference dividers, gain-setting networks, measurement equipment, bridge circuits, and precision timing circuits. It matters less than the basic value for many indicator or pull-up circuits. Use the band as a clue to the intended series, then confirm TCR, operating temperature range, long-term stability, and power derating in the datasheet.
Frequently asked questions
Does TCR change the nominal ohm value?
No. It describes the expected change as temperature moves from the reference condition.
Is TCR the same as tolerance?
No. Tolerance is an initial value allowance; TCR is temperature-related drift.
Does a lower ppm/K always make a resistor better?
Only for requirements that benefit from lower temperature drift. The correct power, voltage, pulse, construction, and stability ratings still matter.
Source and limits
This guide follows IEC 60062-style resistor color marking practice and the color/value conventions used in common through-hole manufacturer tables. Color decoding identifies the nominal marking; it does not prove that a particular part is genuine, undamaged, correctly installed, or available in the stated power rating.
- Use the Resistor Color Code Calculator as a reading aid, then compare the result with the component body, schematic, bill of materials, and datasheet.
- Gold, silver, faded paint, unusual spacing, and manufacturer-specific marks can create more than one plausible reading.
- Do not use a color-only result as a safety, installation, procurement, customs, or compliance decision.
Related guides
5-Band vs 6-Band explains the final band position; The Chart lists common TCR values; and Tolerance Bands separates initial tolerance from drift.