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Resistance Calculator – Calculate Resistance with Ohm's Law

Find electrical resistance using voltage and current with our resistance calculator. Based on Ohm's Law R = V/I, suitable for circuit analysis and electronics design.

How to Use This Resistance Calculator

1

Select calculation mode

Choose from Ohm's Law (V/I), Power formulas (V²/P or P/I²), or Resistivity (ρL/A).

2

Enter your values

Input the required values based on your selected mode — voltage, current, power, or material properties.

3

Get resistance value

The calculator displays resistance in Ω, kΩ, or MΩ depending on the magnitude.

Understanding Electrical Resistance

Resistance opposes the flow of electric current. It is measured in ohms (Ω) and depends on the material, length, and cross-sectional area of the conductor.

R = V / I (Ohm's Law)
R = V² / P (from Power)
R = P / I² (from Power)
R = ρL / A (Resistivity)

Resistivity of Common Materials

MaterialResistivity (Ω·m)Type
Silver1.59 × 10⁻⁸Conductor
Copper1.68 × 10⁻⁸Conductor
Aluminum2.82 × 10⁻⁸Conductor
Silicon6.4 × 10²Semiconductor
Glass10¹⁰ - 10¹⁴Insulator
Rubber10¹³ - 10¹⁶Insulator

Lower resistivity means better conductivity. Copper is the standard for electrical wiring.

Factors Affecting Resistance

1

Length

Longer wires have more resistance. Double the length, double the resistance.

2

Cross-sectional Area

Thicker wires have less resistance. Double the area, halve the resistance.

3

Temperature

Most conductors increase resistance with temperature. Semiconductors decrease.

Frequently Asked Questions

What is Ohm's Law?
Ohm's Law states that voltage equals current times resistance (V = IR). It is the fundamental relationship in electrical circuits, discovered by Georg Ohm in 1827.
How do I calculate resistance from power?
Use R = V²/P if you know voltage and power, or R = P/I² if you know current and power. These come from combining Ohm's Law with the power formula P = VI.
What is resistivity?
Resistivity (ρ) is an intrinsic material property that describes how strongly a material opposes current. It is independent of shape and size, unlike resistance.
Why does temperature affect resistance?
In conductors, heat causes atoms to vibrate more, increasing collisions with electrons. This raises resistance. In semiconductors, heat frees more charge carriers, lowering resistance.
What is the unit of resistance?
The ohm (Ω) is the SI unit. One ohm equals one volt per ampere. Common prefixes include kΩ (1000 Ω) and MΩ (1,000,000 Ω) for larger values.

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