What is EIRP?

EIRP stands for Effective Isotropic Radiated Power (also known as Equivalent Isotropic Radiated Power). It represents the total power that a theoretical isotropic antenna would need to emit to produce the same signal strength in a specific direction as the actual antenna system being used.

In simpler terms, EIRP measures the actual radiated power from an antenna system, taking into account both the transmitter power and the antenna's ability to focus that power in a particular direction. This metric is essential for understanding how far a wireless signal can travel and how strong it will be at a given distance.

Tool description

This calculator computes EIRP from three input parameters: transmit power, antenna gain, and cable loss. It provides results in three different units (dBm, milliwatts, and watts) for flexibility in different applications. The calculation happens in real-time as you adjust the input values.

How it works

The EIRP calculation uses a straightforward formula:

EIRP (dBm) = Transmit Power (dBm) + Antenna Gain (dBi) - Cable Loss (dB)

The calculator then converts the result to linear units:

  • Milliwatts: mW = 10^(EIRP/10)
  • Watts: W = mW / 1000

Examples

Transmit Power Antenna Gain Cable Loss EIRP (dBm)
20 dBm 6 dBi 2 dB 24 dBm

Features

  • Real-time calculation as you type
  • Results displayed in dBm, milliwatts, and watts simultaneously
  • Accepts decimal values for precise calculations
  • One-click copy for all output values
  • Accounts for cable/connector losses in the calculation

Use cases

  • Regulatory compliance: Verify that your wireless setup meets FCC, ETSI, or other regional EIRP limits before deployment.
  • RF system design: Plan antenna installations by calculating expected radiated power for coverage analysis and link budget calculations.
  • Troubleshooting: Diagnose signal strength issues by understanding how cable losses and antenna choices affect your effective radiated power.

Options explained

Parameter Unit Description
Transmit Power dBm The output power of your transmitter or radio module
Antenna Gain dBi The gain of your antenna relative to an isotropic radiator
Cable Loss dB Total signal loss from cables, connectors, and other components between transmitter and antenna

Tips

  • Remember that every 3 dB increase in EIRP doubles the radiated power
  • Cable loss values can typically be found in manufacturer datasheets, usually specified as loss per meter or per foot
  • Don't forget to include connector losses (typically 0.1-0.5 dB per connector) in your total cable loss
  • For directional antennas, EIRP applies to the direction of maximum gain

FAQ

What's the difference between EIRP and ERP? EIRP uses an isotropic antenna as reference (0 dBi), while ERP (Effective Radiated Power) uses a half-wave dipole as reference (2.15 dBi). EIRP is approximately 2.15 dB higher than ERP for the same system.

Why do I need to subtract cable loss? Cable loss represents power that never reaches the antenna. Coaxial cables, connectors, and other components between the transmitter and antenna absorb some signal energy, reducing the actual power radiated.