EIRP Calculator

Effective Isotropic Radiated Power

Calculate the total power radiated by an antenna system. This tool is essential for engineers and technicians in wireless communication, broadcasting, and satellite systems.

Practical Examples

See how EIRP is calculated in real-world scenarios.

Home Wi-Fi Router

Wi-Fi Router

A standard home Wi-Fi router setup to understand its signal strength.

P: 20 dBm, Loss: 1 dB, Gain: 3 dBi

Satellite Communication

Satellite Uplink

A powerful satellite uplink dish used for broadcasting.

P: 10 W, Loss: 3 dB, Gain: 50 dBi

Cellular Base Station

Cellular Tower

A typical cellular tower panel antenna configuration.

P: 43 dBm, Loss: 2 dB, Gain: 17 dBi

Low-Power IoT Device

IoT Device

A low-power LoRaWAN device for long-range communication.

P: 100 mW, Loss: 0.5 dB, Gain: 2.5 dBi

Other Titles
Understanding EIRP: A Comprehensive Guide
An in-depth look at Effective Isotropic Radiated Power, its calculation, and importance in wireless systems.

What is Effective Isotropic Radiated Power (EIRP)?

  • Defining EIRP
  • The Isotropic Antenna Concept
  • Key Components in EIRP Calculation
Effective Isotropic Radiated Power (EIRP) is a standard unit of measurement used in radio frequency (RF) communications to express the total power that would have to be radiated by a hypothetical isotropic antenna to produce the same signal strength as the actual antenna system in a specific direction. An isotropic antenna is a theoretical, lossless antenna that radiates power uniformly in all directions. While it doesn't exist in reality, it serves as a universal benchmark for antenna performance.
The Isotropic Antenna Concept
Imagine a point source of light in the center of a sphere, radiating light equally in all directions. This is the principle of an isotropic radiator. In the context of RF, it provides a baseline (0 dBi gain) against which all real-world antennas are measured. The 'effectiveness' in EIRP comes from accounting for the directional gain of a real antenna and the losses in the system.
Key Components in EIRP Calculation
The EIRP value is not just the power of the transmitter; it's a holistic measure of the system's performance. It is determined by three critical factors:
1. Transmitter Power Output (Pₜ): The raw power generated by the radio transmitter.
2. Antenna Gain (Gₐ): The ability of the antenna to focus power in a particular direction. It's measured in dBi (decibels relative to isotropic).
3. System Losses (Lₗ): The power lost in the system, primarily in the coaxial cable and connectors between the transmitter and the antenna. This is measured in dB.

Step-by-Step Guide to Using the EIRP Calculator

  • Entering Transmitter Power
  • Specifying System Losses
  • Inputting Antenna Gain
This calculator simplifies the process of determining your system's EIRP. Follow these simple steps to get an accurate result.
Entering Transmitter Power
First, enter the power output of your transmitter. You can provide this value in several common units: Watts (W), milliwatts (mW), dBm (decibels relative to one milliwatt), or dBW (decibels relative to one Watt). Select the appropriate unit from the dropdown menu next to the input field. The calculator will handle the conversion automatically.
Specifying System Losses
Next, input the total losses that occur between the transmitter and the antenna. This value, measured in decibels (dB), should account for the attenuation from the coaxial cable, connectors, and any other components in the transmission line. This is a crucial step, as even small losses can significantly impact the final radiated power.
Inputting Antenna Gain
Finally, enter the gain of your antenna in dBi (decibels-isotropic). The dBi unit compares the antenna's performance to a theoretical isotropic antenna. A higher dBi value indicates a more focused, directional beam. Once all values are entered, click the 'Calculate' button to see the final EIRP and ERP values.

Mathematical Formula and Derivation

  • The Logarithmic Formula (dB)
  • The Linear Formula (Watts)
  • Converting Between Units
Understanding the math behind the calculation provides deeper insight into how the system components interact.
The Logarithmic Formula (dB)
Working with decibels simplifies the calculation by converting multiplication and division into addition and subtraction. The formula is:
EIRP (dBm) = Pt (dBm) - Lc (dB) + G_a (dBi)
Where Pt is the transmitter power in dBm, Lc is the cable/connector loss in dB, and G_a is the antenna gain in dBi.
The Linear Formula (Watts)
In a linear scale (Watts), the formula involves multiplication and division:
EIRP (W) = Pt (W) * 10^((Ga (dBi) - L_c (dB)) / 10)
This form is less common for manual calculations but shows how gain and loss act as multipliers on the transmitter power.
Relationship between EIRP and ERP
Effective Radiated Power (ERP) is similar to EIRP but uses a half-wave dipole antenna as the reference instead of an isotropic antenna. A dipole antenna has a gain of 2.15 dBi. Therefore, the relationship is:
ERP (dB) = EIRP (dB) - 2.15 dB

Real-World Applications of EIRP

  • Satellite Communications
  • Wireless Networking (Wi-Fi)
  • Regulatory Compliance
EIRP is not just a theoretical concept; it's a critical parameter in the design and operation of virtually all wireless systems.
Satellite Communications
In satellite links, maximizing the signal strength at the receiver is paramount. Engineers use EIRP calculations (in what is known as a link budget) to ensure that the signal from the ground station is strong enough to reach the satellite in orbit, and vice versa, overcoming the vast distances and atmospheric losses.
Wireless Networking (Wi-Fi)
When deploying Wi-Fi networks, especially over large areas, network administrators calculate the EIRP of access points to predict coverage areas and ensure reliable connectivity. Using high-gain antennas increases EIRP, allowing the signal to travel further and penetrate obstacles more effectively.
Regulatory Compliance
Government agencies like the FCC (in the US) and ETSI (in Europe) set strict limits on the maximum EIRP for different frequency bands and applications. This is done to prevent interference between different wireless services and to control human exposure to RF energy. Calculating EIRP is essential for system operators to ensure they are legally compliant.

Common Misconceptions and Important Considerations

  • EIRP vs. Transmitter Power
  • Antenna Gain is Not 'Free Power'
  • Importance of Accurate Loss Values
Clarifying common points of confusion helps in using EIRP correctly.
EIRP vs. Transmitter Power
A frequent mistake is to equate the transmitter's power rating with the final radiated power. The EIRP can be significantly higher or lower than the transmitter power, depending entirely on the antenna gain and system losses. A high-gain antenna can result in an EIRP that is many times the transmitter's output.
Antenna Gain is Not 'Free Power'
An antenna does not create power; it only redirects it. High gain is achieved by focusing the available power into a narrower beam. This increases the power in the desired direction at the expense of coverage in other directions. Think of it like the reflector in a flashlight, which focuses the bulb's light into a bright beam.
Importance of Accurate Loss Values
The impact of cable and connector loss is often underestimated. For high-frequency signals, even a few meters of low-quality cable can introduce significant loss, drastically reducing the system's EIRP and overall performance. Always use high-quality components and account for their loss accurately.