How the Resistor Color Code Calculator works

The Resistor Color Code Calculator reads the colored bands printed around a resistor and converts them into resistance, tolerance and—on a 6-band component—temperature coefficient. It can also reverse the calculation and generate the nearest representable band sequence from a resistance value.

The color system and preferred number conventions are standardized internationally. Component markings and values are covered by standards such as IEC 60062.

Four-band resistor formula

The Resistor Color Code Calculator treats a 4-band resistor as two significant digits, a multiplier and a tolerance band. Brown-black-red-gold represents 10 × 100 = 1,000 ohms, or 1 kΩ, with ±5% tolerance. Its expected range is 950 Ω to 1.05 kΩ.

Five-band and six-band resistor formulas

The Resistor Color Code Calculator reads three significant digits on a 5-band resistor before the multiplier, which allows finer value markings. A 6-band resistor uses the same three-digit value plus a temperature-coefficient band in parts per million per degree Celsius. For example, 100 ppm/°C means the resistance may change by about 0.01% for each degree Celsius.

Resistor color values

Black through white represent digits 0 through 9. Multiplier bands use powers of ten; gold represents ×0.1 and silver represents ×0.01. Common tolerance bands include brown for ±1%, red for ±2%, gold for ±5% and silver for ±10%.

Worked example

The Resistor Color Code Calculator shows that for a brown-black-red-gold resistor, the first two bands form 10. The red multiplier adds two powers of ten, producing 1,000 Ω. Gold gives ±5%, so the minimum is 950 Ω and the maximum is 1,050 Ω.

Accuracy and limitations

The Resistor Color Code Calculator cannot identify a physical band automatically, and colors can be difficult to distinguish under poor lighting, and aged components may be faded. Verify uncertain parts with a calibrated multimeter and disconnect the resistor from powered circuitry before measuring. Reverse conversion rounds to the nearest value that the selected band count can represent; it does not guarantee that the value belongs to a commercially stocked preferred-value series.

Frequently asked questions

How do I know which end to read first?

Look for the tolerance band, often gold or silver, spaced farther from the other bands. Begin reading from the opposite end.

Why do 5-band resistors have three digits?

Three significant digits allow more precise markings, which are common on 1% and tighter resistors.

What does the sixth band mean?

It gives the temperature coefficient in ppm/°C, describing how resistance changes with temperature.

Can a resistor have no tolerance band?

Older 3-band resistors without a tolerance band are commonly interpreted as ±20%; this calculator focuses on 4-, 5- and 6-band codes.

Does the reverse calculator choose a standard stocked resistor?

It generates the nearest band-representable value. Check an E-series table and supplier availability for a real component.

Should I measure a resistor in a powered circuit?

No. Remove power, discharge stored energy and isolate the component when practical before using a meter.