Magnetic Field Straight Wire Calculator

Magnetic Field of a Straight Wire

A long straight conductor carrying electric current creates a circular magnetic field around it. The field strength decreases with distance from the wire and is described by Ampère's law.

Formula

$$B = \frac{\mu_0 I}{2\pi r}$$

$B$ is the magnetic field in teslas, $I$ is the current in amperes, $r$ is the perpendicular distance from the wire in meters, and $\mu_0 = 4\pi \times 10^{-7}$ T·m/A is the permeability of free space.

Key Properties

Field lines form concentric circles around the wire
Field strength is inversely proportional to distance
Direction follows the right-hand rule

Frequently Asked Questions

What is the right-hand rule for a straight wire?

Point your thumb along the current direction. Your curled fingers show the magnetic field direction around the wire.

How does distance affect the magnetic field?

The field decreases as 1/r. Doubling the distance halves the field strength.

What value should I use for μ₀?

Use 4π × 10⁻⁷ T·m/A (approximately 1.257 × 10⁻⁶ T·m/A) for calculations in free space.

Does this formula work for any wire length?

It applies when the wire is much longer than the distance r. For short wires, use the Biot-Savart law.

What are typical field strengths?

A 10 A current at 5 cm produces about 40 μT — comparable to Earth's magnetic field (~25–65 μT).

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Magnetic Field Straight Wire Calculator

Magnetic Field of a Straight Wire

Formula

Key Properties

Frequently Asked Questions

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