eirp calculator

What Is EIRP?

EIRP stands for Effective Isotropic Radiated Power. It is a standardized way to describe how much power your system appears to radiate in its strongest direction, compared with an ideal isotropic antenna.

In practical RF work—Wi-Fi, point-to-point links, telemetry, ham radio, and IoT—EIRP is critical because regulations are often written as a maximum EIRP, not just a maximum transmitter output.

EIRP Formula

The calculator uses this standard link-budget expression:

Where total losses can include feedline loss, connector loss, filters, lightning arrestors, and other inline attenuation.

Useful Conversions

• dBW = dBm - 30
• dBm = dBW + 30
• Watts = 10^(dBm/10) / 1000
• ERP ≈ EIRP - 2.15 dB (because ERP references a dipole instead of an isotropic radiator)

How to Use This EIRP Calculator

• Enter transmitter power and choose the correct unit (dBm, dBW, or watts).
• Add amplifier gain if your chain includes an RF power amplifier.
• Enter antenna gain in dBi from your antenna datasheet.
• Subtract realistic losses (coax, connectors, jumpers, etc.).
• Optionally add a regulatory limit in dBm to quickly check compliance.

Quick Example

Suppose you have:

• Transmitter output: 30 dBm
• Amplifier gain: 10 dB
• Antenna gain: 15 dBi
• Total losses: 2 dB

Then your EIRP is: 30 + 10 + 15 - 2 = 53 dBm. That is about 200 watts EIRP.

Why EIRP Matters

1) Regulatory Compliance

Many bands have strict EIRP caps. Exceeding those limits can lead to interference complaints, fines, or forced shutdowns.

2) Link Budget Accuracy

Underestimating EIRP can cause overdesign and unnecessary hardware cost. Overestimating it can make your predicted range look better than real-world results.

3) Interference Control

Higher EIRP increases both coverage and interference risk. Good RF engineering balances reliability with spectral responsibility.

Common Mistakes to Avoid

• Mixing dBi and dBd without converting.
• Forgetting cable and connector losses in long runs.
• Confusing transmitter power with radiated power.
• Assuming “legal in one country” means legal everywhere.
• Ignoring amplifier gain compression at high drive levels.

Final Notes

This tool is ideal for fast planning and sanity checks. For mission-critical systems, include real component tolerances, measured cable loss versus frequency, antenna pattern effects, and local legal requirements.