Resistor Color Code Calculator
Calculate resistance from color bands.
About Resistor Color Code Calculator
Resistor color bands encode resistance value. Colors: black=0, brown=1, red=2, ..., white=9.
$$R = (band1 \times 10 + band2) \times multiplier$$
How to use this calculator
- Choose the first two color bands to get the leading digits of the resistance.
- Choose the multiplier band to scale those digits by a power of ten.
- If needed, include the tolerance band to see how much the real value can vary.
- Read the result in ohms, then compare it with the resistor you need for your circuit.
The formula explained
The formula finds the resistance from the first two color bands and the multiplier band. It combines the two digit bands into a number, then multiplies by the power of ten for the final resistance.
- band1 = the digit value of the first color band
- band2 = the digit value of the second color band
- multiplier = the power of ten set by the third color band
- R = the resistance in ohms
Step by step method
- Read the first color band as the first digit and the second color band as the second digit.
- Combine those digits into a number, then multiply by the multiplier value.
- Write the result in ohms.
- If there is a tolerance band, use it to estimate how far the actual resistor can be from the stated value.
Worked example
Problem. Find the resistance of a resistor with bands brown, black, red.
- Brown is \(1\), black is \(0\), so the first two digits make \(10\).
- Red is the multiplier \(10^2\), so compute \(R = 10 \times 100\).
- The resistance is \(1000\ \Omega\).
Answer. \(1000\ \Omega\)
Tips and common mistakes
- Make sure you read the resistor in the correct direction, usually from the end where the bands are closer together or where the tolerance band is separated.
- Do not mix up the multiplier band with a digit band, because that changes the resistance by a factor of ten or more.
Frequently asked questions
How do I use the resistor color code calculator?+
Choose the colors for each band on the resistor, then read the resistance value the tool calculates from them. It applies the standard color-to-digit mapping and multiplier so you can convert the band pattern into ohms.
What does the formula R = (band1 × 10 + band2) × multiplier mean?+
The first two bands give the significant digits of the resistance, and the multiplier band tells you how many times to scale that number. For example, if the first two bands are 4 and 7 and the multiplier is 100, the resistance is 47 × 100 = 4700 ohms.
How does the calculator handle tolerance bands?+
Tolerance bands do not change the resistance value itself, they show how much the actual resistor can vary from the calculated value. This means a 100 ohm resistor with 5% tolerance can measure anywhere from about 95 to 105 ohms.
What if the resistor has 4 bands, 5 bands, or 6 bands?+
A 4 band resistor usually uses two significant digits, a multiplier, and a tolerance band. A 5 band or 6 band resistor uses three significant digits before the multiplier, and a 6 band resistor may also include a temperature coefficient band.
What is the difference between the color bands and the actual resistance value?+
The color bands encode the nominal resistance, which is the printed or expected value, not always the exact measured value. Real resistors can differ slightly because of tolerance, age, and temperature.
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