EIRP / ERP Calculator
Calculate Effective Isotropic Radiated Power (EIRP) and Effective Radiated Power (ERP) from transmitter output power, antenna gain and system losses.
Transmitter Output Power
= 43.00 dBm
Antenna Gain
System Losses
Other losses: splitters, filters, jumpers, etc.
Does not affect EIRP — shown in results for reference.
| dBm | dBW | Power | |
|---|---|---|---|
| EIRP | 57.50 | 27.50 | 562.341 W |
| ERP | 55.35 | 25.35 | 342.768 W |
Formulas & Unit Conversions
EIRP & ERP
EIRP (dBm) = P_tx (dBm) + G_ant (dBi) − L_cable − L_connector − L_other
ERP (dBm) = EIRP (dBm) − 2.15
Unit conversions
dBm → W: P_W = 10^((dBm − 30) / 10)
W → dBm: dBm = 10·log₁₀(P_W) + 30
dBd → dBi: add 2.15 dB (dipole reference offset)
dBi → dBd: subtract 2.15 dB
Typical System Values
The calculated EIRP feeds directly into a link budget analysis. On the receiver side, interference margin and noise figure determine the usable SNR. High feeder losses can also introduce PIM products that degrade receiver sensitivity independently of EIRP.
| Component | Typical value | Notes |
|---|---|---|
| BTS/gNB conducted power | 43–46 dBm | Per carrier, at antenna port |
| Sector antenna gain | 14–21 dBi | Varies by frequency and beamwidth |
| Feeder cable loss | 1–4 dB | Depends on cable length and type |
| Connector loss | 0.3–0.5 dB/pair | N-type, 7/16 DIN |
| EIRP (macro cell) | 55–65 dBm | 350 W – 3 kW equivalent |
| EIRP (small cell) | 30–43 dBm | 1 W – 20 W equivalent |
Frequently Asked Questions
What is EIRP and how is it calculated?▾
EIRP (Effective Isotropic Radiated Power) is the total power a transmit system radiates in its direction of maximum gain, referenced to a theoretical isotropic antenna that radiates equally in all directions. It is calculated as: EIRP (dBm) = P_tx (dBm) + G_ant (dBi) − L_total (dB), where P_tx is the transmitter output power at the antenna port, G_ant is the antenna gain in dBi, and L_total is the sum of all passive losses (cable, connectors, splitters). EIRP is the standard metric for regulatory compliance with bodies such as the FCC, Ofcom, and ITU-R.
What is the difference between EIRP and ERP?▾
EIRP (Effective Isotropic Radiated Power) uses an isotropic antenna (0 dBi) as its reference, while ERP (Effective Radiated Power) uses a half-wave dipole antenna (2.15 dBi) as its reference. The relationship is: ERP (dBm) = EIRP (dBm) − 2.15 dB, or equivalently ERP (W) = EIRP (W) / 1.64. EIRP is the more common metric in modern cellular and 5G regulatory frameworks; ERP is still used in some legacy broadcast and land-mobile regulations.
Why does antenna gain reduce EIRP in the calculator?▾
Antenna gain does not reduce EIRP — it increases it. Only losses (cable, connector, splitter) reduce EIRP. Antenna gain is additive: a 17 dBi sector antenna on a 43 dBm transmitter with 2 dB cable loss gives EIRP = 43 + 17 − 2 = 58 dBm. Regulators typically limit EIRP to prevent interference, which is why high-gain antennas require proportional reductions in transmit power to stay within the permitted EIRP ceiling.
What are typical EIRP limits for cellular base stations?▾
EIRP limits vary by regulator and frequency band. As examples: 3GPP TS 37.105 defines conducted power limits per carrier; the FCC Part 27 rules for AWS/PCS bands set limits in terms of conducted power plus antenna gain; Ofcom's UK interface requirements typically specify maximum EIRP. For 5G NR macro cells, EIRP can reach 65–75 dBm per sector. Indoor small cells are often capped at 24–30 dBm EIRP under licence-exempt rules (e.g. EN 301 908).