Resistor Calculator
The Resistor Calculator decodes the resistance value from the color bands printed on a resistor. It is a handy tool for electronics students, hobbyists, and technicians who need to identify resistor values quickly without memorizing the color code.
Resistor Calculator
What the result means
The first two bands represent the first two digits of the resistance value. The multiplier band determines the power of ten applied to those digits. For example, red-red-red means 2-2 with a ×100 multiplier, giving 2,200 Ω (2.2 kΩ).
How to use this calculator
- 1Select the color of the first significant digit band.
- 2Select the color of the second significant digit band.
- 3Select the color of the multiplier band.
- 4Press Calculate to see the decoded resistance value in ohms.
- 5Use the result to verify the resistor matches your circuit requirement.
The formula
The calculation uses a standard, verifiable formula. Here it is in its simplest form.
Resistance = (Digit1 × 10 + Digit2) × 10^Multiplier
Color code:
Black = 0, Brown = 1, Red = 2, Orange = 3, Yellow = 4
Green = 5, Blue = 6, Violet = 7, Grey = 8, White = 9
What each variable means
| Symbol | Name | Description |
|---|---|---|
| D1 | First digit | The first significant digit from the first color band. |
| D2 | Second digit | The second significant digit from the second color band. |
| M | Multiplier | The power of ten applied to the two-digit number. |
Step-by-step example
Example: Red-Red-Red bands
First band:Red (2)Second band:Red (2)Multiplier:×100 (Red)
- 1First digit = 2 (Red)
- 2Second digit = 2 (Red)
- 3Two-digit number = 22
- 4Multiplier = ×100
- 5Resistance = 22 × 100 = 2,200 Ω = 2.2 kΩ
Result
2,200 Ω (2.2 kΩ)
What changes the result
- The tolerance band (usually gold or silver) indicates how much the actual resistance can vary from the stated value.
- Standard resistor values follow the E-series (E12, E24, etc.) for preferred numbers.
- Surface-mount resistors use a numeric code instead of color bands.
Edge cases to be aware of
Unusual situations handled correctly
- Black as the first band is unusual but valid — it gives a leading zero.
- A multiplier of black (×1) means the resistance is just the two-digit number.
- Four-band and five-band resistors have additional tolerance and precision bands.
Common mistakes
Avoid these errors
- Reading the bands from the wrong end of the resistor.
- Confusing the multiplier band with a tolerance band.
- Forgetting that the multiplier is a power of ten, not a direct multiplication.
Assumptions
- The resistor uses the standard 4-band color code.
- The bands are read from left to right with the tolerance band on the right.
- The color code follows the standard IEC 60062 convention.
Limitations
- Does not decode tolerance or temperature coefficient bands.
- Assumes the standard 4-band format; 5-band and 6-band resistors are not supported.
- Color perception differences can lead to misreading bands.
Frequently asked questions
How do I read a resistor color code?+
Read the bands from left to right. The first two bands are the first two digits, the third band is the multiplier (power of ten), and the fourth band (if present) is the tolerance.
What does the tolerance band mean?+
The tolerance band (gold = ±5%, silver = ±10%) indicates how much the actual resistance can vary from the stated value. A 100 Ω resistor with ±5% tolerance can be anywhere from 95 Ω to 105 Ω.
Why are there standard resistor values?+
Standard values follow the E-series, which uses logarithmic spacing so that any required resistance can be found within a small tolerance. This reduces the number of different values manufacturers need to produce.