Resistance Calculator

The Ohm Resistance Calculator allows users to quickly determine resistance values, tolerances, and conductor properties. It can also calculate combined series or parallel resistances, making it useful for both electronics hobbyists and engineers designing circuits.

What is Electrical Resistance?

Electrical resistance is a property of a material or component that opposes the flow of electric current. It is measured in ohms (Ω) and depends on the material, length, cross-sectional area, and temperature of the conductor.

How to Calculate Resistance?

Resistance can be calculated using Ohm's law:

R = V / I

R = Resistance (ohms, Ω)
V = Voltage (volts, V)
I = Current (amperes, A)

Resistance by Colour Codes

Resistors are marked with colored bands that indicate their resistance, tolerance, and sometimes temperature coefficient. The bands are read from left to right, with the tolerance band on the far right.

Our calculator interprets these colour codes to provide accurate resistance values for:

3-Band Resistors
4-Band Resistors
5-Band Resistors
6-Band Resistors

Use the colour table below to decode resistor values:

Color	Significant Figures	Multiplier	Tolerance	Temperature Coefficient
Black	0	×1		250 ppm/K
Brown	1	×10	±1%	100 ppm/K
Red	2	×100	±2%	50 ppm/K
Orange	3	×1k	±0.05%	15 ppm/K
Yellow	4	×10k	±0.02%	25 ppm/K
Green	5	×100k	±0.5%	20 ppm/K
Blue	6	×1M	±0.25%	10 ppm/K
Violet	7	×10M	±0.1%	5 ppm/K
Grey	8	×100M	±0.01%	1 ppm/K
White	9	×1G
Gold		×0.1	±5%
Silver		×0.01	±10%
None			±20%

Series and Parallel Resistances

Series: When resistors are connected end-to-end, total resistance is the sum:

\(R_{total} = R_1 + R_2 + R_3 + ... + R_n\)

Parallel: When resistors are connected across the same two points, total resistance is:

\(R_{total} = \dfrac{1}{\dfrac{1}{R_1} + \dfrac{1}{R_2} + \dfrac{1}{R_3} + ... + \dfrac{1}{R_n}}\)

Conductor Resistance Calculation

Resistance of a conductor depends on its length, cross-sectional area, and material conductivity:

\(R = \dfrac{L}{A \cdot C}\)

Where:

L = Length of the conductor
A = Cross-sectional area
C = Conductivity of the material

How to Use the Circuit Resistance Calculator

To calculate resistance:

Select the type of resistance calculation (single, series, parallel, or conductor)
Enter the resistor values or select colour codes
Provide conductor dimensions and material if needed
Click “Calculate” to get the total resistance and tolerance

The tool provides instant results, saving time and reducing errors in circuit design.

Applications of Resistance Calculator

Designing electronic circuits
Checking resistor values before installation
Calculating total resistance for series and parallel networks
Estimating conductor resistance for electrical wiring
Educational demonstrations and electronics labs

FAQs

What is the unit of resistance?

The unit of resistance is the ohm (Ω).

How is resistor tolerance represented?

Tolerance is indicated by the last color band on the resistor and shows the possible variation from the nominal value.

Can I calculate resistance without a resistor color code?

Yes, by using Ohm’s law or the conductor resistance formula, you can calculate resistance using voltage, current, or material properties.

References:

From the source of Wikipedia: Electrical Resistance and Conductance, Ohm's law, Series and parallel circuits From Khan Academy: Current and Resistance From Coursehero: Resistors and Resistivity

1^st Band:
black	brown	red	orange	yellow
green	blue	violet	grey	white
2^nd Band:
black	brown	red	orange	yellow
green	blue	violet	grey	white
3^rd Band:
black	brown	red	orange	yellow
green	blue	violet	grey	white
Tolerance Color:
black	brown	red	orange	yellow
green	blue	violet	grey	white
gold	silver
Multiplier Color:
brown	red	orange	yellow	green
blue	violet	grey	gold	silver
Temperature Coefficient Color:
black	brown	red	orange	yellow
green	blue	violet	grey