Resistor Calculator

Category: Physics
- April 04, 2025
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Calculate resistor values using color bands or determine the color bands for a given resistance value. This calculator supports 4-band, 5-band, and 6-band resistors with temperature coefficients.

Select Operation

Resistor Type

Options

About Resistor Color Codes

Resistors use color bands to indicate their resistance value, tolerance, and sometimes temperature coefficient. The standard color code system helps engineers and technicians identify resistor values without using measuring equipment.

Color Code Chart
Color Digit Value Multiplier Tolerance Temp. Coeff. (ppm/°C)
Black 0 ×1 - -
Brown 1 ×10 ±1% 100
Red 2 ×100 ±2% 50
Orange 3 ×1,000 - 15
Yellow 4 ×10,000 - 25
Green 5 ×100,000 ±0.5% -
Blue 6 ×1,000,000 ±0.25% 20
Violet 7 ×10,000,000 ±0.1% 10
Grey 8 ×100,000,000 ±0.05% 5
White 9 ×1,000,000,000 - 1
Gold - ×0.1 ±5% -
Silver - ×0.01 ±10% -
Types of Resistors by Band Count
  • 4-Band Resistors: Most common type with two significant digits, a multiplier, and a tolerance band
  • 5-Band Resistors: Higher precision resistors with three significant digits, a multiplier, and a tolerance band
  • 6-Band Resistors: Highest precision with three significant digits, a multiplier, a tolerance band, and a temperature coefficient band
Reading Resistor Color Bands

To read a resistor's value:

  1. Orient the resistor with the tolerance band (gold/silver/etc.) to the right
  2. Read the color bands from left to right
  3. For 4-band resistors: First two bands are digits, third is multiplier, fourth is tolerance
  4. For 5-band resistors: First three bands are digits, fourth is multiplier, fifth is tolerance
  5. For 6-band resistors: Like 5-band, with the sixth band indicating temperature coefficient
Temperature Coefficient

The temperature coefficient (in ppm/°C) indicates how much the resistance changes with temperature:

  • A lower value means more stability across temperature changes
  • Only found on high-precision 6-band resistors
  • Calculated as: ΔR/R = α × ΔT where α is the temperature coefficient

What Is the Resistor Calculator?

The Resistor Calculator is a handy tool that helps you find a resistor's value based on its colour bands, or the other way round. It supports standard 4-band, 5-band, and 6-band resistors, making it straightforward to decode resistance values without needing manual charts or electrical measuring tools.

Whether you're identifying a resistor in a circuit or planning components for a new project, this calculator makes the process easier and enhances accuracy.

Key Features

  • Instantly convert colour bands to resistance values
  • Find the correct colour bands for a specific resistance value
  • Support for 4-band, 5-band, and 6-band resistors
  • Includes options for tolerance and temperature coefficient
  • Visual resistor diagram for better understanding
  • Step-by-step breakdown of each calculation

How to Use the Calculator

You can choose between two main functions:

1. Colours to Resistance Value

  • Select "Colours to Resistance Value" at the top
  • Pick the resistor type (4, 5, or 6 bands)
  • Use the dropdowns to select each colour band
  • Click "Calculate" to see the resistance, tolerance, and (if applicable) temperature coefficient

2. Resistance Value to Colours

  • Select "Resistance Value to Colours"
  • Enter the resistance value and unit (Ω, kΩ, or MΩ)
  • Choose the tolerance and temperature coefficient (if needed)
  • Click "Calculate" to see the corresponding colour bands

Formula for Resistor Calculation

4-Band Resistor:
R = (D1 × 10 + D2) × Multiplier ± Tolerance%
5-Band / 6-Band Resistor:
R = (D1 × 100 + D2 × 10 + D3) × Multiplier ± Tolerance%
(6-Band includes an additional temperature coefficient in ppm/°C)

Why This Tool Is Useful

This calculator allows you to quickly verify resistor values without the hassle of decoding charts or formulas manually. It's particularly useful when:

  • Working on electronics repairs or builds
  • Learning about electronics and practising resistor identification
  • Checking the accuracy of resistors in your parts collection
  • Teaching students about resistor colour codes and value interpretation

Frequently Asked Questions (FAQ)

What do the colour bands mean?

Each colour represents a digit, a multiplier, or a tolerance. In 6-band resistors, there's also a temperature coefficient band.

What’s the difference between 4, 5, and 6-band resistors?

  • 4-Band: 2 digits, multiplier, and tolerance
  • 5-Band: 3 digits, multiplier, and tolerance
  • 6-Band: Same as 5-band with an extra band for temperature coefficient

What is a temperature coefficient?

It indicates how much the resistance value changes with temperature, measured in ppm/°C (parts per million per degree Celsius). Lower values mean more stability.

Do I need to know all resistor codes?

No. This calculator is designed so you don’t have to memorise anything. Just select or input what you know, and it does the rest.

Can I visualise the resistor?

Yes. The calculator provides a visual representation based on your selections, which aids in learning and validation.

Final Notes

The Resistor Calculator saves time and eliminates guesswork when working with resistors. It's an efficient solution for anyone involved in electronics—from beginners to professionals.