EIRP to ERP Calculator
Convert Effective Isotropic Radiated Power (EIRP) to Effective Radiated Power (ERP) and display equivalent power in multiple engineering units.
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Math
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Related
Enter parameters and click Calculate to view results
Formula & Theory
ERP(dBm)=EIRP(dBm)-2.15This formula is used to calculate antenna parameters for eirp to erp calculator.
Overview
The EIRP to ERP Calculator converts Effective Isotropic Radiated Power (EIRP) into Effective Radiated Power (ERP) using the standard 2.15 dB reference difference between an isotropic radiator and a half-wave dipole. It calculates ERP in dBm, dBW, watts, milliwatts, and microwatts, while also displaying the equivalent linear power ratio. This calculator is useful for RF engineers, wireless network designers, amateur radio operators, satellite communication professionals, broadcast engineers, and students performing RF power conversions, link budget calculations, and regulatory compliance checks.
Input Guide
Enter EIRP exactly in the units shown by this eirp to erp. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- EIRP — use dBm.
Output Guide
The results describe the calculated eirp to erp values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.
How This Calculator Works
The EIRP to ERP uses ERP(dBm)=EIRP(dBm)-2.15. Supply EIRP (dBm) in the displayed units, then use the calculated values as the first engineering target for this rf conversion design or analysis.
Design Notes
EIRP and ERP describe the effective transmitted power of an antenna system but use different reference antennas. EIRP is referenced to an ideal isotropic radiator, whereas ERP is referenced to a half-wave dipole. Since a half-wave dipole has approximately 2.15 dBi of gain over an isotropic radiator, ERP is always 2.15 dB lower than EIRP for the same transmitted signal. Understanding this relationship is essential when interpreting equipment specifications, comparing wireless systems, performing RF link budget calculations, and complying with regional transmission power regulations.
Build and Tuning Notes
Use the converted ERP values when comparing equipment specifications or verifying compliance with regulatory limits that are defined in ERP rather than EIRP. Confirm transmitter output power, antenna gain, and feedline losses before calculating the original EIRP, and verify final RF output using calibrated power meters or spectrum analysers where required. During system deployment, minimise cable losses, maintain proper impedance matching, and ensure that the effective radiated power remains within the legal limits for the operating frequency band.
Frequently Asked Questions
What is the difference between EIRP and ERP?
EIRP is referenced to an ideal isotropic radiator, while ERP is referenced to a half-wave dipole antenna. ERP is always approximately 2.15 dB lower than EIRP because a half-wave dipole has 2.15 dBi of gain relative to an isotropic radiator.
How do you convert EIRP to ERP?
To convert EIRP to ERP, subtract 2.15 dB from the EIRP value. The equation is ERP (dBm) = EIRP (dBm) − 2.15.
Why is the conversion offset 2.15 dB?
The 2.15 dB difference represents the gain of an ideal half-wave dipole antenna relative to an isotropic radiator. This is the internationally accepted reference offset used in RF engineering.
Where is ERP commonly used?
ERP is commonly used in broadcast engineering, amateur radio, land mobile radio systems, television and FM broadcasting, wireless communication, and regulatory documentation where transmission power is specified relative to a half-wave dipole antenna.
Why do some regulations specify ERP instead of EIRP?
Some national and regional regulators define transmitter power limits using ERP because it has historically been the standard reference for many terrestrial radio systems. Others use EIRP, especially for satellite and microwave communication.
Can I convert ERP back to EIRP?
Yes. Simply add 2.15 dB to the ERP value to obtain the equivalent EIRP. The relationship is reversible because the reference difference is constant.
Alex Warren
B.Sc. in Electrical & Electronic Engineering (EEE)
Alex specialises in antenna design and wave propagation. His expertise helps ensure these calculators present practical RF concepts, useful design estimates, and clear engineering guidance for students, HAM operators, and wireless professionals.