EIRP Calculator

About the EIRP Calculator

The EIRP (Effective Isotropic Radiated Power) calculator determines the total radiated power in the direction of maximum antenna gain, accounting for transmitter output power, antenna gain, and cable/connector losses. EIRP is the fundamental parameter in RF link budget analysis and regulatory compliance.

EIRP represents the power that would need to be fed to a hypothetical isotropic antenna (radiating equally in all directions) to produce the same signal strength in the direction of maximum gain as the actual antenna system. It combines transmitter power (in dBm or watts), antenna gain (in dBi), and feed system losses (cable, connectors, filters) into a single figure that describes the system's radiated performance.

Telecommunications engineers, amateur radio operators, and wireless system designers use EIRP for link budget calculations, regulatory compliance verification, RF safety assessments, and coverage planning. This calculator supports multiple power and gain units, computes both EIRP and ERP, and provides a complete link budget showing received power and power density at various distances.

When This Page Helps

EIRP calculation is essential for RF system design, from Wi-Fi access points and cellular base stations to satellite communications and amateur radio. This calculator simplifies link budget analysis by combining transmitter power, antenna gain, and losses into EIRP, then projecting signal strength at various distances. It's indispensable for compliance verification and coverage planning.

How to Use the Inputs

1. Enter the transmitter output power in your preferred unit (W, mW, dBm, or dBW)
2. Enter the antenna gain in dBi (isotropic reference) or dBd (dipole reference)
3. Enter total cable and connector losses in dB
4. Specify the operating frequency in MHz for path loss calculations
5. Enter a target distance for received power and field strength analysis
6. Review EIRP, ERP, free space path loss, and power density results
7. Use the link budget table to assess coverage at various distances

Example Calculation

Tips & Best Practices

• Always subtract cable and connector losses — they can be significant at frequencies above 1 GHz
• Check regional EIRP limits before deploying any wireless system
• Use dBi for EIRP calculations; convert from dBd by adding 2.15 dB
• At 5 GHz, even 10 m of standard coax can lose 6+ dB — use low-loss cable or mount the radio at the antenna
• For indoor propagation, add 10–20 dB to free space path loss to account for walls and multipath

When To Use This Calculator

Calculate Effective Isotropic Radiated Power from transmitter power, antenna gain, and cable losses with link budget and power density analysis. Use it when you need a repeatable calculation in the physics / general category and want the setup, result, and supporting values kept together. This is especially helpful when small input changes, unit choices, or rounding decisions can change the final number.

How To Check The Result

Start by confirming that the inputs match the formula shown on the page. Then compare the main output with the worked example and any secondary values shown by the calculator. If the result will be used in another calculation, keep extra precision until the final step and record the assumptions beside the number.

Practical Notes

Treat the result as a calculation aid rather than a substitute for context. For schoolwork, include the formula and substitution steps. For planning, technical, financial, or health-related decisions, verify important numbers against primary records, current rules, or a qualified professional before acting on them.

Frequently Asked Questions

• What is the difference between EIRP and ERP?

  EIRP references an isotropic antenna, while ERP references a half-wave dipole. ERP = EIRP − 2.15 dB, since a dipole has 2.15 dBi gain.

• Why is EIRP important for regulations?

  Most countries limit EIRP for each frequency band to prevent interference. For example, Wi-Fi is typically limited to 36 dBm (4 W) EIRP in many regions.

• What does dBi vs dBd mean?

  dBi is gain relative to an isotropic (point) radiator. dBd is gain relative to a dipole antenna. dBi = dBd + 2.15.

• How does cable loss affect EIRP?

  Cable loss directly reduces EIRP watt-for-watt. At microwave frequencies, even short cable runs can lose several dB, so keeping cables short and using low-loss types is critical.

• What is free space path loss?

  FSPL is the signal attenuation due to the geometric spreading of the electromagnetic wave, following the inverse square law. It increases with both frequency and distance.

• How does EIRP relate to coverage range?

  Higher EIRP extends coverage range, but the relationship is logarithmic. Doubling EIRP (+3 dB) extends range by only about 41% in free space.