ERP / EIRP Calculator
Use this tool to calculate Effective Radiated Power (ERP) and Equivalent Isotropically Radiated Power (EIRP) from transmitter power, line losses, and antenna gain.
What is effective radiated power (ERP)?
Effective Radiated Power is a way to describe how much useful RF power an antenna system radiates in its strongest direction, compared to a half-wave dipole antenna. ERP is widely used in broadcast, land-mobile, public safety, and compliance documents.
In real systems, transmitter output is not the same as radiated output. Feedline losses, connector losses, filters, and antenna gain all affect the final number. This calculator combines those factors so you can estimate ERP quickly and consistently.
ERP formula used in this calculator
The calculator uses standard logarithmic RF math:
- ERP (dBW) = Tx Power (dBW) − Total Loss (dB) + Antenna Gain (dBd)
- EIRP (dBW) = ERP (dBW) + 2.15
- Watts = 10^(dBW/10)
Why the 2.15 dB difference?
A dipole has 2.15 dB gain over an isotropic radiator. So:
- To convert dBi to dBd: subtract 2.15
- To convert ERP to EIRP: add 2.15 dB
How to use this calculator correctly
- Enter transmitter power in watts, dBm, or dBW.
- Add all line and passive component losses in dB.
- Enter antenna gain in dBd or dBi, matching your antenna datasheet.
- Click Calculate to get ERP and EIRP in dBW, dBm, and watts.
Worked example
Suppose your transmitter output is 50 W, feedline loss is 1.5 dB, additional losses are 0.5 dB, and antenna gain is 6 dBd.
- 50 W = 16.99 dBW
- Total losses = 2.0 dB
- ERP = 16.99 − 2.0 + 6.0 = 20.99 dBW
- ERP in watts = about 125.6 W
- EIRP = 20.99 + 2.15 = 23.14 dBW (about 206.2 W)
Common mistakes to avoid
1) Mixing dBi and dBd
Antenna manufacturers often publish gain in dBi. If a regulation expects ERP, you need dBd. This is one of the most common causes of incorrect filings.
2) Ignoring component loss
Real systems include jumpers, connectors, duplexers, and filters. Even small losses can reduce radiated power significantly.
3) Confusing conducted power with radiated power
Conducted power at the radio output port is not the same as radiated power at the antenna. ERP/EIRP accounts for system effects between those points.
When to use ERP vs EIRP
Use whichever reference your standard, license, or authority specifies:
- ERP references a dipole (common in some broadcasting and regional regulations).
- EIRP references an isotropic radiator (common in satellite, Wi-Fi, and many global technical specs).
Quick practical checklist
- Confirm gain unit (dBi or dBd) from the antenna sheet.
- Measure or estimate cable loss at the operating frequency.
- Include all passive insertion losses.
- Document assumptions for repeatable engineering work.
Final note
This calculator is ideal for engineering estimates and planning. For certification or legal compliance, always confirm with calibrated measurements, local regulations, and your organization’s RF compliance process.