Resistor Calculator

Decode 4-band resistor color codes into resistance and tolerance.

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Band 1

Band 2

Multiplier

Tolerance

Result

Enter values to calculate.

Summary

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Detail

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Decode a 4-band resistor's color code into its resistance value in ohms, plus the minimum and maximum resistance range based on its tolerance band.

How It Works

How Resistor Calculator Works

On a standard 4-band resistor, the first two bands represent significant digits (each color from black through white maps to a digit 0-9), the third band is a power-of-ten multiplier, and the fourth band indicates tolerance as a percentage. The calculator combines the first two digits (first digit × 10 + second digit) and multiplies by the third band's multiplier value to get the base resistance.

The tolerance band then defines how far the actual resistance could realistically vary from that calculated (nominal) value — for example, a 5% tolerance means the real resistor could measure anywhere within 5% above or below the calculated figure, which the calculator shows as a minimum and maximum range.

Worked Example

See It In Action

A resistor with bands brown-black-red-gold decodes to digits 1 and 0 (giving 10), multiplied by the red band's ×100, for a nominal resistance of 1,000 ohms (1 kΩ) — with gold's ±5% tolerance, the real value falls somewhere between 950 and 1,050 ohms.

Real-World Use Cases

Who Uses Resistor Calculator and Why

Identifying an unlabeled resistor pulled from a parts bin by reading its color bands.
Verifying a resistor's value matches a circuit schematic before soldering it into place.
Checking whether a resistor's tolerance range is tight enough for a precision application like a voltage divider or filter.
Teaching or learning the resistor color code system for an electronics class or hobby project.

Common Mistakes

Mistakes to Avoid

Reading the bands starting from the wrong end — the tolerance band (often gold or silver, and usually spaced slightly apart from the others) marks the end you should read backward from.
Using this calculator on a 5-band or 6-band resistor — those use an extra significant-digit band and decode differently, so applying the 4-band method gives a wrong value.
Confusing a resistor's physical color with a similar-looking one under poor lighting — brown and red, or green and blue, can be easy to misread without good light.

Pro Tips

Tips for Best Results

If you're unsure which end to start reading from, look for the tolerance band (commonly gold, silver, or occasionally brown/red) — it's normally isolated with a slightly larger gap and should be read last, not first.
For precision circuits (timing, filters, voltage references), check the tolerance band closely — a 1% brown-tolerance resistor gives far more predictable behavior than a 10% silver one.

Troubleshooting

Fixing Common Problems

My decoded value doesn't match what a multimeter reads on the actual resistor. — Confirm you read the bands in the correct direction and didn't misidentify a color under dim lighting — if the multimeter reading falls within the calculated min/max tolerance range, the resistor is still within spec even if it's not exactly the nominal value.

I have a resistor with 5 or 6 bands and the values don't line up. — This calculator is built for standard 4-band resistors only — a 5-band or 6-band resistor uses a third significant-digit band (and sometimes a temperature coefficient band) that needs a different decoding table.

Glossary

Terms Explained

Tolerance band: The final color band on a resistor indicating how far its actual resistance may vary from the calculated nominal value, expressed as a percentage.

Multiplier band: The third band on a 4-band resistor, indicating the power-of-ten value the first two digits are multiplied by.

FAQ

Frequently Asked Questions

How do I remember what each color represents?

Many people use a mnemonic phrase where each word's first letter matches a color in order (black, brown, red, orange, yellow, green, blue, violet, gray, white = 0 through 9) — search for "resistor color code mnemonic" for common versions.

Does this work for 5-band or 6-band resistors?

No — this calculator is built specifically for standard 4-band resistors. 5-band and 6-band resistors use an extra significant-digit band (and sometimes a temperature coefficient band) and need a different decoding method.

Why does tolerance matter for circuit design?

In precision circuits, a resistor's actual value affects things like voltage dividers, filter frequencies, and timing circuits — tighter tolerance (like 1% vs. 10%) means more predictable, consistent behavior across multiple units.

What are the most common tolerance colors?

Gold (±5%) and silver (±10%) are the most common on general-purpose resistors, while brown (±1%) is typical on precision resistors used in more sensitive circuits.