What formula does this calculator use?

It calculates S = P_EIRP/(4πd²) and E = √(Z₀S), using free-space impedance Z₀ = 376.730313 Ω. This is nearly the familiar approximation E = √(30P_EIRP)/d. EIRP equals transmitter power times linear antenna gain.

EIRP (Effective Isotropic Radiated Power) is the total power a theoretical isotropic antenna would need to emit to produce the same field strength in the target direction. It equals transmitter power multiplied by the linear antenna gain.

What distance is required for the far-field formula to be valid?

The far-field (Fraunhofer region) begins at approximately d = 2D²/λ, where D is the antenna aperture and λ is the wavelength. For electrically small antennas this distance is typically a few wavelengths. Results near or in the near-field will be inaccurate.

How is dBuV/m calculated from V/m?

dBuV/m = 20 × log10(E_Vm × 1,000,000). This converts the field strength in V/m to decibels relative to one microvolt per meter, the unit commonly used in EMC and broadcast standards.

How are electric and magnetic field strength related?

For a plane wave in the far field, H = E/Z₀, where the free-space wave impedance Z₀ is approximately 376.730313 ohms. This relationship is not valid as a generic near-field antenna model.

Does this account for reflections or terrain?

No. The calculator assumes ideal free-space conditions with no ground reflections, multipath, or obstructions. Real-world field strengths can differ significantly due to these effects.

Can this determine RF-exposure compliance or a safe distance?

No. Compliance assessment depends on jurisdiction, frequency, averaging time, duty cycle, simultaneous sources, antenna pattern, near-field conditions and accessible geometry. Use the applicable current standard and a qualified assessment.

RF Field Strength Calculator

Calculate ideal far-field free-space EIRP, electric field (V/m and dBµV/m), magnetic field (A/m and dBµA/m), and power density. This is not an RF-exposure compliance result.

Transmitter Parameters

Transmitter Power

Antenna Gain (dBi)

Distance from Antenna

Quick Presets

Enter transmitter parameters and click Calculate

Formula Reference

E (V/m) = sqrt(30 × P_EIRP) / d

P_EIRP (W) = P_tx (W) × 10^G_dBi/10

S (W/m²) = P_EIRP / (4πd²)

E (V/m) = sqrt(376.730313 × S)

E (dBuV/m) = 20 × log10(E × 10⁶)

H (A/m) = E / 376.730313

H (dBµA/m) = 20 × log10(H × 10⁶)

Method, sources and privacy

The E/H relationship assumes a plane wave in ideal free space and is intended for far-field engineering estimates. It does not model antenna near fields, reflections, terrain, duty cycle, simultaneous transmitters or regulatory exposure averaging.

Privacy: parameters and results remain in this browser tab; this calculator sends no RF inputs to a calculation service.

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Summary

Calculate ideal far-field free-space EIRP, electric field (V/m and dBµV/m), magnetic field (A/m and dBµA/m), and power density. This is not an RF-exposure compliance result.

How it works

Enter the transmitter output power in watts (W) or dBm.
Enter the antenna gain in dBi (decibels relative to an isotropic radiator).
Enter the distance from the antenna to the measurement point in meters.
Click Calculate to apply S = P_EIRP/(4πd²) and E = √(Z₀S), with Z₀ = 376.730313 Ω.
The result shows electric field strength (V/m), power density (W/m²), and field strength in dBuV/m.
Use the unit toggles to switch between watts/dBm and meters/feet.

Use cases

Perform an ideal far-field free-space screening calculation.
Convert a calculated V/m result to dBµV/m.
Design wireless link budgets and coverage zones.
Calculate antenna field intensity for EMC pre-compliance testing.
Cross-check EIRP and inverse-square calculations.
Convert between field strength units (V/m, dBuV/m, mW/m²).
Validate antenna range test setups and calibration distances.
Estimate received signal strength in RF propagation planning.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu