Science & Lab Tools
Resistor Calculator
Calculate resistor values using color codes and find the right resistor for your circuit
Reviewed by the calculator.uk.com Team · Last reviewed 5 June 2026 · Our methodology
Select color bands to calculate resistance value
Related to Resistor Calculator
The Resistor Calculator helps you determine the resistance value of a resistor based on its color bands. Electronic resistors use a standardized color-coding system to indicate their resistance value and tolerance. This calculator supports 5-band resistors, which provide more precise resistance values than 4-band resistors.
Color Code System
Each color represents a specific numerical value:
• Black: 0
• Brown: 1
• Red: 2
• Orange: 3
• Yellow: 4
• Green: 5
• Blue: 6
• Violet: 7
• Gray: 8
• White: 9
The calculator uses these color values to compute the final resistance. The first three bands represent significant digits, the fourth band (multiplier) determines the number of zeros to add, and the fifth band indicates the tolerance or accuracy of the resistor value.
The calculator provides comprehensive information about the resistor's specifications, helping you understand both the nominal value and its acceptable range.
Resistance Value
The main resistance value is displayed in ohms (Ω), kilohms (kΩ), or megohms (MΩ) depending on the magnitude. This is the nominal or intended resistance value of the component.
Tolerance
The tolerance percentage indicates how much the actual resistance may deviate from the nominal value. For example, a ±5% tolerance means the actual resistance could be up to 5% higher or lower than the nominal value.
Value Range
The minimum and maximum values show the acceptable range based on the tolerance. Any resistance measurement within this range indicates a properly functioning resistor.
1. Why are there different tolerance bands?
Different tolerance bands indicate the precision of the resistor. Tighter tolerances (e.g., ±1% or ±0.5%) are used in applications requiring precise resistance values, while wider tolerances (e.g., ±5% or ±10%) are suitable for less critical applications and are generally more cost-effective.
2. What's the difference between 4-band and 5-band resistors?
4-band resistors use two digits for the value, while 5-band resistors use three digits, providing more precise values. For example, a 4-band resistor might show 47kΩ, while a 5-band resistor could show 47.5kΩ. The extra digit in 5-band resistors allows for more precise resistance values.
3. How do I read the resistor bands correctly?
Hold the resistor with the tolerance band (usually gold or silver) on the right. Read the color bands from left to right: the first three bands give the significant digits, the fourth band is the multiplier, and the fifth band indicates tolerance. The gap between the bands is usually wider near the tolerance band to help with orientation.
4. Why do my measurements differ from the calculated value?
Actual resistance measurements may vary from the nominal value due to several factors: manufacturing tolerances, temperature effects, aging, and measurement equipment accuracy. As long as the measured value falls within the tolerance range, the resistor is considered acceptable for use.
5. What is the scientific source for this calculator?
The value, multiplier, and tolerance bands used here follow the resistor color code carried in IEC 60062, the international standard for marking resistors and capacitors, which formalized the coding scheme originally published as EIA RS-279 by the Electronic Industries Alliance. This is the same color code resistor manufacturers have printed on axial-lead components since the mid-20th century.