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Resistor Calculator

Decode 4-band and 5-band resistor colour codes, or calculate total resistance for resistor lists in series and parallel.

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Resistor calculator: decode 4-band and 5-band colour codes or combine resistor values

A resistor calculator can either decode common resistor colour bands into resistance and tolerance, or combine a list of resistor values to find the total resistance for series and parallel networks.

What this resistor calculator covers

This page handles two common resistor workflows. In decode mode, it reads 4-band and 5-band resistor colour codes and returns the nominal resistance together with the tolerance range. In list mode, it totals any number of resistor values in either series or parallel.

That combination makes the tool useful for both bench work and quick design checks. You can identify a physical resistor from its bands, then compare how multiple resistors behave when they are wired together in a simple circuit.

How resistor colour code decoding works

A 4-band resistor uses the first two bands as significant digits, the third band as the multiplier, and the fourth band as the tolerance. A 5-band resistor extends that pattern by using three significant-digit bands before the multiplier and tolerance bands.

Once the significant digits and multiplier are known, the nominal resistance follows directly. The tolerance band then defines the allowed range around that nominal value, which is why the calculator shows minimum and maximum resistance as well as the centre value.

Nominal resistance = Significant digits x Multiplier

The significant digits come from the first two or three bands, depending on whether the resistor is a 4-band or 5-band part.

Tolerance range = Nominal resistance x (1 ± Tolerance%)

Applies the tolerance percentage to show the lowest and highest likely resistance.

Series and parallel resistor formulas

Series resistors add directly because the same current passes through each component one after the other. Parallel resistors reduce the total resistance because current can split across multiple paths.

The calculator accepts plain values or common suffixes such as k and M, then converts everything into ohms before computing the total. That keeps list mode flexible enough for quick part-bin calculations and simple network checks.

R_total(series) = R1 + R2 + R3 + ...

Adds every resistor directly when they are wired in one path.

1 / R_total(parallel) = 1 / R1 + 1 / R2 + 1 / R3 + ...

Uses the reciprocal sum when the resistors share the same voltage in parallel branches.

When to trust the result and when to go further

This tool is accurate for standard fixed-resistor colour bands and ideal series or parallel combinations. It is a strong first pass for resistor identification, LED current-limiting checks, pull-up and pull-down selection, and quick equivalent-resistance planning.

It does not model temperature coefficient, non-linear components, mixed resistor networks that are not purely series or purely parallel, or the way a real circuit might behave once the resistor is connected to a wider load. For critical designs, confirm the part rating and the surrounding circuit assumptions before finalizing a build.

Frequently asked questions

What is the difference between a 4-band and 5-band resistor?

A 4-band resistor uses two significant-digit bands before the multiplier, while a 5-band resistor uses three. Five-band parts are common when tighter tolerance or more precise nominal values are needed.

 Why is total resistance lower in parallel?

Parallel branches create additional current paths, so the equivalent resistance seen by the source falls below the value of the smallest individual branch resistor.

 Can I enter 4.7k or 1M in the list mode?

Yes. The list parser accepts common suffixes such as k for kilohms and M for megaohms, as well as plain ohm values separated by commas, semicolons, or line breaks.

 Does the calculator handle mixed resistor networks?

No. List mode only handles pure series or pure parallel combinations. A mixed network has to be simplified in stages before you can calculate its total resistance accurately.

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