Colour code · SMD code · EIA-96
Resistor calculator: colour code and SMD code
Read any resistor: type the code printed on an SMD part, or pick the colour bands of a through-hole one. Below: how the codes work, and how to size a resistor for an LED in a car.
How SMD codes work
| Code | Read as | Value |
|---|---|---|
| 103 | 10 × 10³ | 10 kΩ |
| 472 | 47 × 10² | 4.7 kΩ |
| 4R7 | R is the decimal point | 4.7 Ω |
| 1002 | 100 × 10² (1 % parts) | 10 kΩ |
| 01C | EIA-96: code 01 = 100, C = × 100 | 10 kΩ |
| 68X | EIA-96: code 68 = 499, X = × 0.1 | 49.9 Ω |
| 000 | zero-ohm jumper | 0 Ω |
Colour code
| Colour | Digit | Multiplier | Tolerance |
|---|---|---|---|
| Black | 0 | × 1 | |
| Brown | 1 | × 10 | ±1 % |
| Red | 2 | × 100 | ±2 % |
| Orange | 3 | × 1 k | |
| Yellow | 4 | × 10 k | |
| Green | 5 | × 100 k | ±0.5 % |
| Blue | 6 | × 1 M | ±0.25 % |
| Violet | 7 | × 10 M | ±0.1 % |
| Grey | 8 | ±0.05 % | |
| White | 9 | ||
| Gold | × 0.1 | ±5 % | |
| Silver | × 0.01 | ±10 % |
4 bands: two digits, multiplier, tolerance. 5 bands: three digits, multiplier, tolerance. Hold the resistor with the tolerance band (often gold or set apart by a wider gap) on the right.
A resistor for an LED in a car
R = (supply − LED forward voltage) ÷ current. Use 14.4 V, not 12 V — that is what the circuit sees with the engine running. A red LED (2 V) at 20 mA: (14.4 − 2) ÷ 0.02 = 620 Ω.
Power in the resistor: I² × R = 0.02² × 620 ≈ 0.25 W, so use a 0.5 W resistor for margin. Ready-made 12 V LED strips and bulbs already have their resistor or driver built in.
How to use the calculator
- SMD: type the code exactly as printed, letters included (4R7, 01C).
- Colour bands: choose 4 or 5 bands and pick each colour from the left.
- Measure with a multimeter (ohms, out of circuit) when the marking is unclear — parts in a circuit read lower because of the parallel paths.
Questions
Why is 103 not 103 Ω?
The last digit is the number of zeros: 10 followed by three zeros, 10 000 Ω = 10 kΩ. A 103 Ω part would be marked 1030 or 103R.
What does the R in 4R7 mean?
It is the decimal point: 4R7 = 4.7 Ω, R47 = 0.47 Ω.
What is an EIA-96 code?
A two-digit code for precision (1 %) values from the E96 series plus a letter for the multiplier, used on parts too small for four digits.
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