Calculate the Resistance
Select the colors in reading order, starting from the left side.
Formula Used
A is the first color digit. B is the second color digit. M is the multiplier exponent from the third color.
For brown, black, and red, A is 1, B is 0, and M is 2. The resistance is (10 × 1 + 0) × 102, which equals 1,000 Ω.
How to Use This Calculator
- Hold the resistor so the three value bands read left to right.
- Choose the first color for the tens digit.
- Choose the second color for the ones digit.
- Choose the third color for the multiplier.
- Select Calculate Resistance to place the result above the form.
- Compare the result with your circuit diagram or meter reading.
Example Color Codes
| First band | Second band | Multiplier | Calculation | Resistance |
|---|---|---|---|---|
| Brown (1) | Black (0) | Red (×100) | 10 × 100 | 1 kΩ |
| Red (2) | Violet (7) | Yellow (×10,000) | 27 × 10,000 | 270 kΩ |
| Green (5) | Blue (6) | Gold (×0.1) | 56 × 0.1 | 5.6 Ω |
| Yellow (4) | Violet (7) | Silver (×0.01) | 47 × 0.01 | 0.47 Ω |
Understanding Three-Band Resistors
A three-band resistor uses colors to show its nominal resistance value. The first two bands provide significant digits. The third band sets the multiplier. Technicians often read bands from left to right. Start at the band nearest one end. A clear reading prevents wrong substitutions. Wrong values can change voltage, current, heat, or timing. The calculator shows numeric steps behind the answer clearly.
What Each Color Represents
Black represents zero. Brown represents one. Red represents two. Orange represents three. Yellow represents four. Green represents five. Blue represents six. Violet represents seven. Grey represents eight. White represents nine. The first band supplies the tens digit. The second band supplies the ones digit. The multiplier then scales that base number. Red multiplies by one hundred. Yellow multiplies by ten thousand. Gold divides by ten. Silver divides by one hundred. Lighting can make similar shades difficult to distinguish.
Why the Multiplier Matters
The multiplier creates the final resistance range. It changes a small two-digit number into an electrical value. For example, red, violet, and yellow means twenty-seven times ten thousand. The result is two hundred seventy thousand ohms. That value is often written as 270 kilohms. Green, blue, and gold gives fifty-six times one tenth. The result is 5.6 ohms. Ignoring it produces an incorrect result.
Using the Reading in Circuit Work
Resistance controls current in many circuits. It can limit current through an LED. It can set a transistor bias point. It can form a voltage divider. It can set a timing constant with a capacitor. A wrong resistor may dim an LED. It may overheat a component. Compare the calculated value with your circuit diagram. Then check the resistor with a meter. Three-band parts normally omit a tolerance band. Their tolerance is commonly assumed from the series or documentation.
Good Handling and Verification Habits
Read resistor bands under bright neutral light. Clean dirty parts before inspection. Avoid guessing between blue and violet. Avoid confusing grey with white. Use a digital meter for confirmation. Disconnect one lead for accurate in-circuit testing. Parallel paths can distort a meter reading. Let hot resistors cool first. Heat can alter readings temporarily. Inspect for burnt paint or cracked bodies. Damaged parts should be replaced. Record values when troubleshooting repeated faults. Keep common resistor ranges in labeled storage. Organized parts reduce selection errors.
Limits of a Three-Band Reading
Three bands give a nominal value only. They do not show precision directly. Four-band resistors add a tolerance band. Five-band resistors add another significant digit. Six-band types may include temperature information. This calculator is designed for standard three-band patterns. It includes gold and silver multiplier choices. These options cover many low-value components. Specialty markings may use other conventions. Surface-mount resistors use printed codes instead. Check manufacturer data for unusual devices. Use the calculated value as a starting point. Confirm critical designs with measurements and specifications.
Frequently Asked Questions
1. What does a three-band resistor show?
It shows two significant digits and one multiplier. Together, those colors produce the nominal resistance in ohms. A three-band resistor usually does not include a separate tolerance color.
2. Which side of the resistor should I read first?
Read from the side where the grouped color bands begin closest to one end. The multiplier band is normally separated slightly from the first two bands.
3. Can black be the first or second band?
Yes, black represents zero in the color system. However, a leading black digit can produce unusual values. Check the circuit, package marking, and meter reading when the result seems unexpected.
4. What does a gold third band mean?
A gold multiplier means multiply the two-digit value by 0.1. For example, green, blue, and gold gives 56 × 0.1, which equals 5.6 ohms.
5. What does a silver third band mean?
A silver multiplier means multiply the two-digit value by 0.01. Yellow, violet, and silver gives 47 × 0.01, which equals 0.47 ohms.
6. Why is my meter reading different?
The resistor may have manufacturing variation, heat effects, damage, or parallel circuit paths. Disconnect one lead before measuring. Then compare the reading with the nominal calculated value.
7. Does this calculator show tolerance?
No. Standard three-band codes give the nominal value only. Check the resistor series, documentation, or packaging for the tolerance when a separate tolerance band is absent.
8. What unit does the result use?
The calculation is based on ohms. Larger values are displayed as kilohms or megohms for easier reading. The exact value in ohms is also shown after calculation.
9. Can this tool read four-band resistors?
It can calculate the first three bands only. A four-band resistor adds tolerance. Use the first two digits and multiplier here, then read the fourth band separately.
10. Are grey and white easy to confuse?
They can look similar under poor lighting. Use bright neutral light, compare against a color chart, and confirm important values with a digital multimeter.
11. Is the calculated value safe for circuit design?
It is a useful starting value. Also check resistor power rating, tolerance, voltage limits, temperature behavior, and your circuit requirements before installing a component.