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Resistor Calculator

Decode 3–6 band resistor color codes, combine resistors in series or parallel, and calculate round-wire conductor resistance.

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Resistor Color Code

ExampleSample values — edit any field to see your result.

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Resistance

52 MΩ ±5%

Estimated result

Resistance in ohms
52,000,000Ω
Tolerance
±5%

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Compare scenarios

Keep a baseline, then change an assumption to see its effect side by side.

Band interpretation

BandColorMeaning
1greenfirst digit
2redsecond digit
3bluemultiplier
4gold±5%
Resistance52 MΩ ±5%
Decode three-, four-, five-, or six-band resistor colors, combine any list of resistors in series or parallel, or calculate the resistance of a round conductor.

How to use this calculator

Choose the band count and read the bands in the direction indicated by the component markings. Confirm the tolerance band before accepting the value. The tolerance describes a permitted range around nominal resistance, not a guarantee of an exact measured resistance.

Examples

Green, red, blue, gold

Green and red form 52, blue multiplies by 10⁶, and gold is ±5%, giving 52 MΩ ±5%.

Copper conductor

A 100 m copper conductor, 0.05 cm in diameter, at 59,600,000 S/m has 8.5452318438602 Ω resistance.

Formula

Color code: R = significant digits × 10^multiplier.

Series: Rtotal = ΣR. Parallel: Rtotal = 1 / Σ(1/R).

Round conductor: R = length / (conductivity × π × (diameter/2)²).

For parallel entries, every branch must have a positive resistance. A zero-ohm branch represents a short circuit and needs separate treatment.

Interpretation limits

Color decoding assumes the selected band count and reading direction are correct. Verify the part marking or measure it out of circuit when that can be done safely. Tolerance describes the permitted value range, while a six-band temperature coefficient describes change per kelvin; neither is a power rating. Series and parallel formulas assume ideal resistors and the conductor mode uses a constant conductivity at an unspecified reference temperature. It does not model contact resistance, skin effect, temperature rise, insulation, ampacity, or allowable voltage drop.

Frequently asked questions

How do resistor color bands work?
The first bands are significant digits, followed by a power-of-ten multiplier, tolerance, and on six-band resistors a temperature coefficient.
How do resistors add in series?
Series resistances add directly, R total = R1 + R2 + more.
How do resistors combine in parallel?
The reciprocal total is the sum of reciprocals, 1/R total = 1/R1 + 1/R2 + more.
What controls a wire's resistance?
Resistance grows with length and falls with conductivity and cross-sectional area.

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