EIRP Calculator (Effective Isotropic Radiated Power)

EIRP is the apparent power a perfectly isotropic antenna would need to match your directional system.

How the Math Works

The EIRP Calculator uses the fundamental formula EIRP = Pt + Gain - Loss to determine Effective Isotropic Radiated Power. This equation combines transmitter power (Pt) with antenna gain and subtracts system losses to calculate the actual radiated power as if the signal were broadcast equally in all directions from a point source. The calculation is performed in decibels (dB), where gains are expressed as positive values and losses as negative values, allowing them to be simply added or subtracted. For example, a 10W transmitter (10 dBW) with 20 dBi antenna gain and 2 dB system losses would yield an EIRP of 28 dBW (10 + 20 - 2 = 28).

Practical Applications

To use this calculator for practical wireless system design, enter your transmitter's output power in dBW or convert from watts using the formula dBW = 10 × log10(Power in watts). Add the antenna's gain in dBi, which represents how much the antenna focuses energy compared to an isotropic reference antenna. Subtract any system losses such as cable attenuation, connector losses, and filter losses. This calculation is essential for Wi-Fi network planning, satellite communications, broadcast television, and cellular tower deployments where understanding your actual radiated power helps ensure regulatory compliance and optimal coverage.

Day-to-Day Use

Understanding EIRP helps explain why your smartphone or Wi-Fi router can maintain strong connections across rooms and neighborhoods. When you stream high-definition video without buffering at your local coffee shop, or make clear video calls from your home office, EIRP calculations ensure the signal strength is sufficient to reach your device. This same principle applies to cell phone towers that provide coverage in your area, satellite dishes receiving television broadcasts, and wireless internet services delivering connectivity to rural communities. Without proper EIRP calculations, modern wireless communication would be unreliable, and many conveniences like cordless phones, wireless earbuds, and smart home devices would struggle to function properly.

Worked example

30 dBm + 12 dBi − 2 dB → 40 dBm = 10 W EIRP.

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