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Resistance Calculator

Resistance in an electric circuit is the opposition to current flow. It is measured in ohms (Ω) and represents the power loss caused by voltage as current flows.

Resistance matters because it controls current flow and keeps circuits stable; resistors are used to adjust voltage or measure current. Resistance is also needed to convert electrical energy and minimize losses.

For example, a light bulb uses resistance to regulate current, producing heat and light. Many circuits also use resistors to stabilize voltage or control current in a specific part. Resistance is therefore an essential component of electronic devices and circuits.

Resistance

Resistance Calculation Method

Resistance is calculated using Ohm's law, expressed as V = IR, where V is voltage (volts), I is current (amperes), and R is resistance (ohms). Resistance is thus defined as the ratio of voltage to current.

R = V / I
The resistance (Ω) is 0 .

About This Calculator

Electrical resistance is how strongly a component opposes the flow of current; it is measured in ohms (Ω). Given any two of voltage, current and resistance you can find the third with Ohm's law, the foundation of circuit analysis.

Enter voltage and current to find resistance, or any other pair to find the missing value.

Resistance is voltage divided by current, and combinations follow simple rules: series resistances add, parallel resistances add as reciprocals. Two 6 Ω resistors give 12 Ω in series but 3 Ω in parallel, and a 100 Ω paired with a 10 Ω in parallel gives 9.09 Ω, dominated by the smaller value.

Key Formula:R = V / I (Ω = V / A) · V = I × R · I = V / R

Frequently Asked Questions

What is Ohm's law?

Ohm's law states that current through a conductor is proportional to the voltage across it: V = I × R. Rearranged, R = V / I and I = V / R let you solve for any single unknown when the other two are known.

What is the resistance of a typical resistor?

Common through-hole resistors range from a few ohms to about 1 MΩ, with 220 Ω, 1 kΩ and 10 kΩ among the most used values in hobby electronics. The colored bands on the body encode the value.

Does resistance change with temperature?

Yes. For most metals resistance rises as temperature increases, which is why a hot filament has much higher resistance than a cold one. Special resistors called thermistors are designed to use this effect as a sensor.

Why is parallel resistance smaller than either resistor?

Parallel paths give the current more routes, so the same voltage drives more current and the resistance must be lower. The total is always smaller than the smallest individual resistance.

How does temperature affect resistance?

In metals resistance rises with temperature as lattice vibrations scatter electrons, about 0.4 % per kelvin for copper. In semiconductors and thermistors resistance falls with temperature, which is what makes them useful as sensors.

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Sources & last update

2026-10-19