Resistor Calculators

Tools for electronics engineers and hobbyists

Resistor Color Code Calculator

Select the number of bands and colors to calculate the resistance value.

Resistance: 0Ω ±0%

How to Read Resistor Color Codes

Resistor color codes use colored bands to indicate resistance value, tolerance, and sometimes temperature coefficient.

  • 4-band: 2 digits, multiplier, tolerance
  • 5-band: 3 digits, multiplier, tolerance
  • 6-band: 3 digits, multiplier, tolerance, temperature coefficient

SMD Resistor Calculator

Enter SMD code (e.g., 103, 1002, 4R7):

Resistance: 0Ω

SMD Resistor Code Examples:

  • 103 = 10 × 10³ = 10,000Ω (10kΩ)
  • 1002 = 100 × 10² = 10,000Ω (10kΩ)
  • 4R7 = 4.7Ω
  • 0R1 = 0.1Ω
  • R10 = 0.10Ω

Series Resistors Calculator

Enter resistor values to calculate the equivalent resistance in series.

R₁ R₂ R₃

The equivalent resistance will be shown here.

Parallel Resistors Calculator

Enter resistor values to calculate the equivalent resistance in parallel.

R₁ R₂ R₃

The equivalent resistance will be shown here.

Theory of Resistors in Series and Parallel

Resistors in Series

When resistors are connected in series, the equivalent resistance is calculated by adding the individual resistances:

Req = R1 + R2 + R3 + ... + Rn

This means the equivalent resistance is always larger than the largest individual resistor in the series.

Resistors in Parallel

When resistors are connected in parallel, the equivalent resistance is calculated using:

1/Req = 1/R1 + 1/R2 + 1/R3 + ... + 1/Rn

This means the equivalent resistance is always smaller than the smallest individual resistor in the parallel connection.

Special Case for Two Parallel Resistors

For two resistors in parallel, you can use the product-over-sum formula:

Req = (R1 × R2) / (R1 + R2)

Physical Explanation

Series connection: Current has to flow through each resistor one after another, increasing the total resistance.

Parallel connection: Current can flow through multiple paths, decreasing the total resistance.

Voltage Divider Calculator

Calculate output voltage for a simple voltage divider circuit.

Vin R₁ R₂ GND Vout

Voltage Divider Results

Output Voltage (Vout): -

Voltage Division Ratio: -

Current Through Resistors: -

Power Dissipation in R₁: -

Power Dissipation in R₂: -

Voltage Divider Formula

The output voltage of a voltage divider is calculated using:

Vout = Vin × (R₂ / (R₁ + R₂))

Where:

  • Vin is the input voltage
  • R₁ is the upper resistor
  • R₂ is the lower resistor

Note: This formula assumes no load is connected to Vout. If a load is connected, the actual output voltage will be lower.

Resistor Information

Color Code Chart

Color 1st Band 2nd Band 3rd Band Multiplier Tolerance Temp. Coeff.

Common Resistor Values (E12 Series)

The E12 series includes resistors with 10% tolerance with these standard values:

10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82

These values repeat for each decade (e.g., 100, 120, 150, etc.)

Other Standard Series

E6 (20% tolerance): 10, 15, 22, 33, 47, 68

E24 (5% tolerance): Adds intermediate values between E12 values

E96 (1% tolerance): Even more precise values for high-precision applications

Unit Conversions

  • 1 Ohm (Ω) = 1 Volt per Ampere (V/A)
  • 1 kiloOhm (kΩ) = 1,000 Ohms
  • 1 megaOhm (MΩ) = 1,000,000 Ohms
  • 1 gigaOhm (GΩ) = 1,000,000,000 Ohms

Resistor Power Ratings

Common resistor power ratings:

  • 1/8 W (0.125W) - Small signal applications
  • 1/4 W (0.25W) - General purpose
  • 1/2 W (0.5W) - Higher power applications
  • 1 W, 2 W, 5 W - Power resistors

Always ensure your resistor can handle the power dissipation in your circuit!