- Equivalent resistance
- 600 Ω
How it works
Diameter matters through its square
Doubling a round conductor’s diameter gives four times the cross-sectional area and one-quarter the modeled resistance at the same length and conductivity. Distinguish diameter from area when comparing wire dimensions; they affect resistance differently.
Separating a resistor code from circuit resistance
A color-code mode interprets markings on a resistor, while series and parallel modes combine resistance values in a circuit. Choose the matching mode before entering bands or numbers. Tolerance describes an allowed range around a nominal value rather than an extra resistance to add. A conductor-resistance estimate also depends on the material and dimensions specified in its separate mode.
Series or parallel: formula and assumptions
Series: R = ΣRᵢ. Parallel: 1/R = Σ(1/Rᵢ).
Resistances must be positive.
Four-band color code: formula and assumptions
Resistance = (10×first digit + second digit) × multiplier.
Read the tolerance band last. This mode covers standard four-band values.
Conductor resistance: formula and assumptions
Resistance = length/(conductivity×π×diameter²/4).
Diameter is converted from millimeters to meters. Conductivity must match the material and temperature.
3, 4, 5 & 6 color bands: formula and assumptions
Resistance = significant digits × color multiplier.
Three bands use two digits and an absent tolerance band (±20%). Five and six bands use three digits; the sixth indicates a temperature-coefficient class.
Worked example
Using the Series or parallel example:
- Resistances (ohms)
- 100, 200, 300
- Connection
- series
Series: R = ΣRᵢ. Parallel: 1/R = Σ(1/Rᵢ).
Example result
Equivalent resistance: 600 Ω
These are illustrative inputs. Change the values to explore a different scenario.
Formula references
References explain the underlying methods; they do not imply endorsement or individual professional review of Finflo.
Common questions
Why is parallel resistance lower than any individual positive branch resistance?
Parallel branches add conductance. Taking the reciprocal of total conductance yields an equivalent resistance below each branch value.
What does the sixth resistor color band represent?
In the supported six-band code, it indicates a temperature-coefficient class; it is not an additional significant resistance digit.
Prepared by Finflo. See our methodology and editorial policy.