Formula and method
Read two significant digits for four bands or three for five bands, multiply by the multiplier band and apply the tolerance percentage.
Tolerance band colors
The tolerance band follows IEC 60062:2016, the same edition used for the temperature coefficient band below. Older charts list gray as ±0.05%; the 2016 edition moved ±0.05% to orange and made gray ±0.01%. A resistor with no tolerance band (three bands only) is ±20%.
| Color | Tolerance |
|---|---|
| Brown | ±1% |
| Red | ±2% |
| Orange | ±0.05% |
| Yellow | ±0.02% |
| Green | ±0.5% |
| Blue | ±0.25% |
| Violet | ±0.1% |
| Gray | ±0.01% |
| Gold | ±5% |
| Silver | ±10% |
| None | ±20% |
Worked example
Brown, black, red and gold represent 10 × 100 = 1,000 Ω with ±5% tolerance, giving limits of 950–1,050 Ω.
Six bands: brown, black, black, brown, brown, red is 100 × 10 = 1,000 Ω, ±1%, 50 ppm/K. A 10 K temperature rise can move it by 1,000 × 50 × 10⁻⁶ × 10 = 0.5 Ω.
The sixth band: temperature coefficient
On six-band resistors the last band gives the temperature coefficient of resistance (TCR) in parts per million per kelvin, so ΔR = R × TCR × ΔT. IEC 60062:2016 assigns these colors:
| Color | TCR (ppm/K) |
|---|---|
| Black | 250 |
| Brown | 100 |
| Red | 50 |
| Orange | 15 |
| Yellow | 25 |
| Green | 20 |
| Blue | 10 |
| Violet | 5 |
| Gray | 1 |
From a resistance to color bands
Round the value to two significant digits for four bands or three for five and six, then write it as digits × 10^n. The digits become color bands, n becomes the multiplier (silver = −2, gold = −1, black = 0 … white = 9), and the tolerance and TCR bands follow.
For 4.7 kΩ: 47 × 10² gives yellow, violet, red; ±5% adds gold. Resistors are stocked in E-series preferred values matched to tolerance: E6 for ±20%, E12 for ±10%, E24 for ±5%, E48 for ±2%, E96 for ±1% and E192 for ±0.5% and tighter. The calculator shows the nearest one, so you can see whether a value is standard (for example, 5,000 Ω is not in E24; 5,100 Ω is).