⚡ Resistor Calculator

Calculate resistor values using color codes, series/parallel combinations, power dissipation, and voltage division. Complete toolkit for engineers and students.

Resistor Color Code

Number of Bands:

4 Bands 5 Bands 6 Bands

1st Band (1st Digit):

2nd Band (2nd Digit):

3rd Band (3rd Digit):

Multiplier Band:

Tolerance Band:

Temperature Coefficient:

Resistor Value

Resistance Value

Tolerance

Value Range

Temperature Coefficient

Standard Values (E12 Series):

1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2

Series/Parallel Resistor Calculator

Configuration Type:

Series Parallel

Resistor Values:

Circuit Diagram:

Total Resistance

Configuration

Series

Formula:

Series: R_total = R₁ + R₂ + R₃ + ...

Resistor Power Calculator

Calculation Mode:

Calculate Power Calculate Resistance Calculate Voltage Calculate Current

Voltage (V):

Current (A):

Resistance:

Power:

Power Dissipated

Calculated Value

Power Rating Warning

Power Formulas:

P = V × I (Power = Voltage × Current)

P = V² / R (Power = Voltage² / Resistance)

P = I² × R (Power = Current² × Resistance)

V = √(P × R) (Voltage from Power and Resistance)

I = √(P / R) (Current from Power and Resistance)

R = P / I² (Resistance from Power and Current)

Voltage Divider Calculator

Input Voltage (Vin):

Load Current (IL):

R1 (Upper Resistor):

R2 (Lower Resistor):

Circuit Diagram:

Output Voltage (Vout)

Divider Current

Voltage Ratio

R1 Power Dissipation

R2 Power Dissipation

Voltage Divider Formulas:

Vout = Vin × (R2 / (R1 + R2))

Voltage Ratio = R2 / (R1 + R2)

Current = Vin / (R1 + R2)

P1 = I² × R1, P2 = I² × R2

Design Tips:

• Use high resistance values to minimize current consumption

• Consider load current effects on output voltage

• Ensure resistor power ratings are adequate

• Use precision resistors for accurate voltage division

Frequently Asked Questions

For a 4-band resistor, read from left to right: the first two bands are significant digits, the third band is the multiplier (number of zeros), and the fourth band is the tolerance. For example, Red-Red-Brown-Gold = 22 × 10¹ = 220Ω ±5%.

5-band resistors have an additional significant digit, making them more precise. 4-band resistors typically have ±5% or ±10% tolerance, while 5-band resistors often have ±1% or ±2% tolerance for precision applications.

For parallel resistors, use the formula: 1/Rtotal = 1/R1 + 1/R2 + 1/R3 + ... The total resistance is always less than the smallest individual resistor value.

For series resistors, simply add all resistance values: Rtotal = R1 + R2 + R3 + ... The total resistance is always greater than any individual resistor value.

Calculate the power dissipation using P = V²/R or P = I²R, then choose a resistor with at least 2x the calculated power rating for safety. Common ratings are 1/8W, 1/4W, 1/2W, 1W, 2W, etc.

Tolerance indicates how much the actual resistance can vary from the nominal value. Lower tolerance (±1%) means higher precision and typically higher cost, while higher tolerance (±5% or ±10%) is suitable for general applications.

Standard values follow E-series: E12 (±10%) has 12 values per decade, E24 (±5%) has 24 values, and E96 (±1%) has 96 values. This ensures consistent availability and reduces manufacturing costs.

Resistors have a temperature coefficient (usually in ppm/°C) that indicates how much the resistance changes with temperature. For precision applications, choose resistors with low temperature coefficients and consider operating temperature ranges.

Disclaimer

This calculator is for educational and reference purposes only. Actual circuit design should consider component tolerances, temperature effects, and safety requirements. For critical applications, always verify calculations and consult professional engineers.