Resistor Calculator – Color Codes, Series/Parallel, and Conductor Resistance

Professional tools to calculate the ohm value and tolerance based on resistor color codes, the total resistance of resistors in parallel or series, and the resistance of a conductor based on size and conductivity.

Resistor Color Code Calculator

Use this calculator to find out the ohm value and tolerance based on resistor color codes.

Resistance Value:

How the color coding works:

The color coding for resistors is an international standard defined in IEC 60062. The first bands represent significant figures, followed by a multiplier band, and finally a tolerance band.

In a typical four-band resistor, the first and second bands represent significant figures. The third band is the multiplier, and the fourth band represents tolerance.

Five-band resistors have an additional significant figure for higher precision, while six-band resistors may include a temperature coefficient band.

Color Significant Figures Multiplier Tolerance Temperature Coefficient
Black 0 × 1 - 250 ppm/K (U)
Brown 1 × 10 ±1% (F) 100 ppm/K (S)
Red 2 × 100 ±2% (G) 50 ppm/K (R)
Orange 3 × 1K ±0.05% (W) 15 ppm/K (P)
Yellow 4 × 10K ±0.02% (P) 25 ppm/K (Q)
Green 5 × 100K ±0.5% (D) 20 ppm/K (Z)
Blue 6 × 1M ±0.25% (C) 10 ppm/K (Z)
Violet 7 × 10M ±0.1% (B) 5 ppm/K (M)
Grey 8 × 100M ±0.01% (L) 1 ppm/K (K)
White 9 × 1G - -
Gold - × 0.1 ±5% (J) -
Silver - × 0.01 ±10% (K) -
None - - ±20% (M) -

Parallel Resistor Calculator

Provide all of the resistance values in parallel, separated by a comma "," and click the "Calculate" button to determine total resistance.

Total Resistance:

Resistors in Parallel:

The total resistance of resistors in parallel is equal to the reciprocal of the sum of the reciprocals of each individual resistor.

Rtotal = 1 / (1/R1 + 1/R2 + 1/R3 + ... + 1/Rn)

When resistors are connected in parallel, the total resistance is always less than the smallest individual resistance in the circuit.

Series Resistor Calculator

Provide all of the resistance values in series separated by a comma "," and click the "Calculate" button to determine total resistance.

Total Resistance:

Resistors in Series:

The total resistance of resistors in series is simply the sum of the resistances of each resistor.

Rtotal = R1 + R2 + R3 + ... + Rn

When resistors are connected in series, the total resistance is always greater than any individual resistance in the circuit.

Resistance of a Conductor

Use the following to calculate the resistance of a conductor. This calculator assumes the conductor is round.

Resistance:

Resistance of a Conductor:

The resistance of a conductor depends on its length, cross-sectional area, and the material's conductivity.

R = L / (A × C)

Where:

  • L is the length of the conductor
  • A is the cross-sectional area of the conductor
  • C is the conductivity of the material

For a round conductor, the cross-sectional area A = π × (d/2)², where d is the diameter.

Test Your Resistor Knowledge

Answer these 10 questions to test your understanding of resistors, color codes, and circuit calculations.

Question 1: Color Code Interpretation

You have a 4-band resistor with colors Brown, Black, Orange, Gold. What is its resistance and tolerance?

Explanation:

Brown = 1, Black = 0, Orange = ×1000, Gold = ±5%

So the resistance is 10 × 1000 = 10,000Ω or 10kΩ with a tolerance of ±5%

Question 2: Series Circuit

You connect 3 resistors: 100Ω, 220Ω, and 330Ω in series. What's the total resistance?

Explanation:

In a series circuit, resistances simply add up:

Rtotal = R1 + R2 + R3

Rtotal = 100Ω + 220Ω + 330Ω = 650Ω

Question 3: Parallel Circuit

Three resistors — 100Ω, 200Ω, and 300Ω — are connected in parallel. Find the total resistance.

Explanation:

In a parallel circuit, the formula is:

1/Rtotal = 1/R1 + 1/R2 + 1/R3

1/Rtotal = 1/100 + 1/200 + 1/300 = 0.01 + 0.005 + 0.00333 = 0.01833

Rtotal = 1/0.01833 = 54.55Ω

Question 4: Mixed Series + Parallel

Two 100Ω resistors are in parallel, and that group is in series with a 150Ω resistor. What's the total resistance?

Explanation:

First, calculate the parallel combination:

1/Rparallel = 1/100 + 1/100 = 0.01 + 0.01 = 0.02

Rparallel = 1/0.02 = 50Ω

Then add the series resistor:

Rtotal = Rparallel + Rseries = 50Ω + 150Ω = 200Ω

Question 5: LED Circuit Design

You want to power a red LED (forward voltage 2V, desired current 20mA) from a 9V battery. What resistor should you use?

Explanation:

Using Ohm's Law: R = (Vsource - VLED) / I

R = (9V - 2V) / 0.02A = 7V / 0.02A = 350Ω

The resistor needs to drop 7V at 20mA, which requires a 350Ω resistor.

Question 6: Conductor Resistance

A copper wire is 5 meters long with a cross-sectional area of 1 mm². Calculate its resistance. (Resistivity of copper = 1.68 × 10⁻⁸ Ω·m)

Explanation:

Using the formula: R = ρ × L / A

Where ρ = 1.68 × 10⁻⁸ Ω·m, L = 5m, A = 1 mm² = 1 × 10⁻⁶ m²

R = (1.68 × 10⁻⁸) × 5 / (1 × 10⁻⁶) = 0.084Ω

Question 7: Tolerance Calculation

You have a 10kΩ resistor with ±10% tolerance. What are the minimum and maximum possible values?

Explanation:

For a 10kΩ resistor with ±10% tolerance:

Minimum value = 10kΩ - (10% of 10kΩ) = 10kΩ - 1kΩ = 9kΩ

Maximum value = 10kΩ + (10% of 10kΩ) = 10kΩ + 1kΩ = 11kΩ

Question 8: Power Rating

You use a 100Ω resistor in a circuit where it drops 10V. What power rating is required for safe operation?

Explanation:

Using the power formula: P = V² / R

P = (10V)² / 100Ω = 100 / 100 = 1W

The resistor dissipates 1W of power, so a 1W resistor would be the minimum required. It's generally recommended to use a resistor with a higher power rating for safety and longevity.

Question 9: 5-Band Resistor

A 5-band resistor has colors: Red, Red, Brown, Brown, Brown. What is its value?

Explanation:

For a 5-band resistor:

First three bands are significant figures: Red = 2, Red = 2, Brown = 1

Fourth band is multiplier: Brown = ×10

Fifth band is tolerance: Brown = ±1%

Value = 221 × 10 = 2210Ω or 2.21kΩ with ±1% tolerance

Correction: I made an error in the options. The correct answer should be 2.21kΩ ± 1%, which corresponds to option c.

Question 10: Voltage Divider

In a voltage divider with R1 = 1kΩ and R2 = 2kΩ connected to a 9V source, what is the output voltage across R2?

Explanation:

In a voltage divider, the output voltage across R2 is:

Vout = Vin × (R2 / (R1 + R2))

Vout = 9V × (2kΩ / (1kΩ + 2kΩ)) = 9V × (2/3) = 6V

Your Results

0/10

Keep practicing to improve your knowledge!

Resistor Calculator: A Complete Guide for Electronics Enthusiasts

Introduction

Whether you're a hobbyist building your first circuit or a seasoned engineer designing complex systems, resistors are fundamental components that you'll use all the time. But quickly converting color codes, combining resistors in series or parallel, or computing conductor resistance by material can be tedious by hand. That's exactly where a resistor calculator comes in handy: it gives you fast, reliable results, avoids mistakes, and saves you from flipping through reference tables.

In this guide, you'll learn:

By the end, you'll know how to get precise resistance values, avoid common pitfalls, and leverage a calculator tool smartly.

What a Resistor Calculator Does

A resistor calculator is more than just a number generator. A good one typically offers multiple functions, including:

These features eliminate manual lookup or repeated formula use. A good example is the tool offered at Calculator Premium, which supports color bands, series/parallel resistance, and conductor resistance.

How Resistor Color Coding Works

Resistors typically display colored bands that encode their value (ohms) and tolerance. This is standardized under IEC 60062. Here's how to read them:

For instance, in a common 4-band resistor:

Say you see: Green – Red – Blue – Gold.

Green = 5, Red = 2 → gives "52"

Blue multiplier = ×1,000,000 → total is 52,000,000 Ω (52 MΩ)

Gold = ±5% tolerance → the resistor's actual value is between 49.4 MΩ and 54.6 MΩ

For more precise components (5-band or 6-band), a third significant-figure band and sometimes a thermal coefficient band are included.

Standard Color Table (simplified)

Color Digit Multiplier Tolerance
Black 0 ×1 —
Brown 1 ×10 ±1%
Red 2 ×100 ±2%
Orange 3 ×1,000 —
Yellow 4 ×10,000 —
Green 5 ×100,000 ±0.5%
Blue 6 ×1,000,000 ±0.25%
Violet 7 ×10,000,000 ±0.1%
Gray 8 ×100,000,000 ±0.01%
White 9 ×1,000,000,000 —
Gold — ×0.1 ±5%
Silver — ×0.01 ±10%

A reliable calculator tool automates all this so you don't need to manually cross-reference tables.

Series vs Parallel: Combining Resistors

Circuits often require combining multiple resistors in series or parallel to achieve a target resistance. Here's how those combinations work:

Resistors in Series

When resistors are connected end-to-end (series), their resistances simply add:

Rtotal = R1 + R2 + R3 + … + Rn

So three resistors of 100 Ω, 200 Ω, and 300 Ω in series yield 600 Ω.

Series connections increase voltage drop across the chain, but current is common through each resistor.

Resistors in Parallel

When resistors are connected with both ends joined (parallel), the combined resistance decreases. The formula is:

1 / Rtotal = 1/R1 + 1/R2 + 1/R3 + … + 1/Rn

Or equivalently:

Rtotal = 1 / (sum of reciprocals)

For example, two resistors of 100 Ω in parallel yield 50 Ω:

1 / R = 1/100 + 1/100 = 0.02 → R = 50 Ω

The Calculator Premium tool (and similar calculators) allow you to enter comma-separated resistor values to compute the equivalent quickly.

Parallel combos are useful when you want to reduce resistance while sharing current paths.

Resistance of a Conductor: Wires, Traces, and Cables

Beyond discrete resistors, you may need the resistance of a wire, PCB trace, or cable. The general formula is:

R = (L / A) × (1 / σ)

Or more commonly:

R = L / (A × σ)

Where:

Alternatively, you can frame the internals as:

R = ρ × (L / A)

Where ρ (rho) is the resistivity (the inverse of conductivity).

A calculator should let you input:

Then it outputs the resistance in ohms. The Calculator Premium version supports material selection (Copper, Aluminum, Gold, Silver, etc.) and dimensional input in multiple units.

Use Cases: When & Why You Need a Resistor Calculator

Here are scenarios where a resistor calculator is highly helpful:

By integrating a calculator into your workflow, you reduce tedious manual lookup errors and speed your design process.

Best Practices & Tips for Accuracy

Disclaimer: This tool is for educational use only. We recommend verifying the results before applying them.

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