PCB Controlled Impedance & Trace Width Calculator
Pick the five colour bands to read resistance, tolerance and min/max range instantly — or enter a target value (Ω / kΩ / MΩ) and get the exact colour code.
| Colour | Digit (bands 1–3) | Multiplier (band 4) | Tolerance (band 5) |
|---|
Formula: R = (B1 × 100 + B2 × 10 + B3) × 10B4 ± B5. Example: yellow–violet–black–red–brown = 470 × 10² Ω = 47 kΩ ±1% (range 46.53 – 47.47 kΩ).
Multiplier colours: silver ×0.01 · gold ×0.1 · black ×1 · brown ×10 · red ×100 · orange ×1 kΩ · yellow ×10 kΩ · green ×100 kΩ · blue ×1 MΩ · violet ×10 MΩ · gray ×100 MΩ · white ×1 GΩ.
Tolerance colours: none ±20% · silver ±10% · gold ±5% · brown ±1% · red ±2% · green ±0.5% · blue ±0.25% · violet ±0.1% · gray ±0.05%.
Notes: ① Five bands give three significant digits — typical of precision (E96) resistors; a sixth band would encode the temperature coefficient in ppm/°C. ② Sub-100 Ω values need the gold / silver multiplier: 4.7 Ω = yellow–violet–black–silver (470 × 0.01). ③ The E24 check is a design aid — always verify the actual value with a multimeter before powering a board.
Frequently Asked Questions
1. How do you read a 5-band resistor?
Hold the resistor so the tolerance band is on the right, then read left to right: bands 1–3 are the significant digits, band 4 is the multiplier, band 5 is the tolerance. Example: yellow–violet–black–red–brown = 4-7-0 × 100 = 47 kΩ ±1%. The full colour chart is built into the calculator.
2. Which end do I start from — how do I find the tolerance band?
The tolerance band is the odd one out: on precision 5-band parts it is usually brown (±1%) or red (±2%) and sits at one end, separated from the digit bands by a slightly wider gap. Gold (±5%) or silver (±10%) tolerance bands are the classic markers on older 4/5-band carbon parts. If the bands are centred or you genuinely cannot tell, measure the part with a multimeter and work backwards — or enter the expected value in the calculator’s Value → Colors mode and compare.
3. What is the difference between a 4-band and a 5-band resistor?
A 4-band resistor encodes two significant digits, a multiplier and a tolerance; a 5-band adds a third significant digit. Three digits give finer resolution (e.g. 4.75 kΩ instead of rounding to 4.7 kΩ), which is why 5-band codes appear on precision metal-film parts, typically with ±1% or tighter tolerance. Everything else — reading direction, multiplier colours, gold/silver rules — works the same.
4. How do I calculate the min and max value from the tolerance band?
Multiply the nominal value by (1 ± tolerance/100). Example: 47 kΩ ±1% → 47,000 × 0.99 = 46.53 kΩ and × 1.01 = 47.47 kΩ, so the part can legitimately measure anywhere in 46.53–47.47 kΩ. The calculator shows this range automatically whenever you pick a tolerance band.
5. Why does my multimeter reading differ from the colour code?
Two normal reasons: (1) the part is within its tolerance — a ±5% “10 kΩ” resistor can read 9.5–10.5 kΩ and still be perfect; (2) your meter has its own accuracy spec (typically ±0.5–1% plus counts) and lead resistance matters below ~100 Ω. If the reading is outside the tolerance range, check for a damaged or overheated part, a wrong value installed, or measurement error (parallel paths on the board, finger contact on the probes).
6. What does the 6th band on some resistors mean?
A sixth band is the temperature coefficient (TCR) in ppm/°C — how much the value drifts with temperature. Common TCR colours: brown = 100 ppm/°C, red = 50, orange = 15, yellow = 25 ppm/°C. TCR matters in precision analog and current-sense circuits; the 5-band calculator ignores it because a 5-band code carries no TCR information.
7. Can the multiplier band be gold or silver?
Yes — gold (×0.1) and silver (×0.01) multipliers exist precisely for sub-100 Ω values. Example: 4.7 Ω = yellow–violet–black–silver (470 × 0.01). These small values are common as current-sense and shunt resistors; the calculator’s reverse mode solves them automatically when you enter a value like 4.7 Ω.
