Resistor Calculator

What this calculator does

The Resistor Calculator converts a resistor color code into an ohm value and a tolerance. Resistor color bands are an international shorthand defined in IEC 60062. Each position means significant digits, a multiplier, tolerance, or a temperature coefficient.

It supports three-, four-, five-, and six-band resistors. Three- and four-band parts encode two significant digits; five- and six-band parts add a third. A six-band part also has a temperature coefficient in ppm/K. The result shows the nominal resistance, the tolerance percentage and letter code, and the minimum and maximum resistance at that tolerance.

How to use this calculator

1. Choose the number of bands on the resistor.
2. Select the color of the first band, the second band, and the third band if the resistor has five or six bands.
3. Select the multiplier color.
4. Select the tolerance color if the resistor has four or more bands.
5. Select the temperature coefficient color for a six-band resistor.
6. Click Calculate.

The default example is a four-band resistor with green, red, blue, and gold bands. Green is 5, red is 2, blue multiplies by 1,000,000, and gold is plus or minus 5%. The result is 52 MΩ with a range of 49.4 MΩ to 54.6 MΩ. The letter J is the tolerance code.

Resistor color code formula

3-band: R = (10 × B1 + B2) × M
4-band: R = (10 × B1 + B2) × M
5-band: R = (100 × B1 + 10 × B2 + B3) × M
6-band: same as 5-band, plus a temperature coefficient

The letter codes in the result follow the common IEC tolerance designators: F for 1%, G for 2%, J for 5%, K for 10%, and M for 20%. A three-band resistor has no tolerance band, so the calculator assumes the standard 20% tolerance shown by the letter M.

What the results mean

The nominal resistance is the value printed by the color code. The tolerance range shows how far the real part may drift from that value. For example, a 1 kΩ resistor with a 1% tolerance can measure anywhere from 990 Ω to 1,010 Ω and still be within specification. The temperature coefficient, when present, tells you how much the resistance changes per degree Kelvin; lower ppm/K values indicate a more stable component.

Gold and silver multipliers are used for values below 10 Ω. Gold multiplies by 0.1 and silver by 0.01. Those colors are valid multiplier bands but cannot be used for significant digits.

Assumptions and limitations

• It decodes the color code only and does not measure a physical resistor or verify its power rating.
• The accuracy of the result depends on reading the colors correctly. Lighting, aging, and color blindness can cause mistakes.
• Five- and six-band resistors are read in the standard order with the tolerance band separated from the other bands.
• Temperature coefficient and reliability bands are sometimes confused. This calculator treats the sixth band as a temperature coefficient.
• It does not calculate series, parallel, or conductor resistance.

Frequently asked questions

How do I know which end to start reading?

Start at the end where the bands are closer together. The tolerance band is usually separated from the other bands by a slightly larger gap. If the resistor has a gold or silver band, that band is almost always the tolerance band.

Why does my measured value differ from the calculator?

Resistors have a tolerance, so a 5% part can legitimately differ by 5% from its nominal value. Measurement error, lead resistance, and temperature also affect the reading. Check the multimeter and the actual band colors before assuming a fault.

What does the letter after the tolerance mean?

The letter is a standardized tolerance code. J means plus or minus 5%, K means plus or minus 10%, F means plus or minus 1%, and M means plus or minus 20%. These codes help when a resistor is too small for full text marking.

Reference table

Resistor color code chart

Read the bands from the end opposite the tolerance band. Four-band resistors use two significant digits and a multiplier; five-band resistors add a third digit. Always confirm with a multimeter before relying on a color reading.

Source

Reference: Calculator.net — Resistor Calculator.

Disclaimer

This calculator provides estimates for educational and planning purposes. Always verify component values and ratings with a multimeter and the component datasheet before using them in a circuit.