RF exposure distance calculator
RF exposure limits cap how much radio energy a person may absorb. This calculator turns transmit power, antenna gain and frequency into the power density in front of the antenna, then into the minimum distance at which that density falls below the FCC or ICNIRP 2020 limit for the public or for trained workers.
Key-down power reaching the antenna. The duty-cycle field below averages it over the compliance window. · = 50.0 dBm
Gain toward the person. Use the main-beam figure for a worst case.
Share of the averaging window the transmitter actually radiates. The limits apply to that average, so 50 % halves the exposure and the 0.1 % of a pulse radar divides it by a thousand.
A fixed beam is the worst case, with the main lobe on the person the whole time. A rotating or scanning beam only sweeps past, and the limits are averaged over 6 or 30 minutes.
0.3–100000 MHz · 30 min averaging time
At 146 MHz the FCC and ICNIRP set the same limit: 2 W/m² for the public and 10 W/m² occupational. Switching the standard changes nothing here. They differ between 300 MHz and 2 GHz, and below 30 MHz only the FCC gives a power-density limit.
A reflecting surface can add to the direct wave. OET 65 uses a 2.56× worst case. The default assumes no reflection.
Where someone actually stands, measured from the antenna.
Side view. The antenna stands at the left, and the shaded area is the zone that has to stay clear under the limit set you picked; its edge is the green arc. The amber dashed arc is the other exposure group of the same standard. The figure stands at the distance you entered and turns amber inside the boundary. Distances are measured from the antenna along the ground scale, which is compressed so a 0.2 m and a 40 m boundary fit in one picture.
The two published tables drawn on log axes. Where a dashed ICNIRP curve lies on top of the solid FCC one the standards agree, which covers the whole 30 to 300 MHz plateau and everything above 2 GHz. They part company only between 300 MHz and 2 GHz, where ICNIRP runs lower. Below 30 MHz ICNIRP publishes no power-density level at all, so the chart starts there.
A main-beam, far-field estimate for guidance only, not a compliance report and not legal advice. It assumes the person stands in the main beam with the full antenna gain and takes the power you enter as the power reaching the antenna. Ground reflection defaults to none, which is the plain free-space figure. Switch it to 2.56 for the rooftop or ground-level worst case that OET 65 recommends. Averaging over 6 or 30 minutes is handled through the duty-cycle field, so enter the key-down power together with the share of the window the transmitter is on. The antenna setting decides whether the beam counts as parked on the person, which is the worst case and not the everyday one, or as sweeping past for beamwidth/360 of the time.
FCC and ICNIRP side by side
The two limit tables are not the same table, so both are shown here for the frequency in the form. The distances use the power, gain, duty cycle and reflection factor you entered.
| Limit set | Limit (mW/cm²) | Limit (W/m²) | Averaging | Minimum distance |
|---|---|---|---|---|
| FCC, general population (uncontrolled) | 0.2 | 2 | 30 min | 3.98 m |
| ICNIRP 2020, general public | 0.2 | 2 | 30 min | 3.98 m |
| FCC, occupational (controlled) | 1 | 10 | 6 min | 1.78 m |
| ICNIRP 2020, occupational | 1 | 10 | 30 min | 1.78 m |
- General public: both allow the same power density at this frequency
- Occupational: both allow the same power density at this frequency
- Units. The FCC publishes mW/cm², ICNIRP publishes W/m². 1 mW/cm² is 10 W/m².
- Band edges. The FCC steps at 300 and 1500 MHz, ICNIRP at 400 MHz and 2 GHz. From 30 to 300 MHz and again above 2 GHz the two agree, and between 300 MHz and 2 GHz ICNIRP comes out lower.
- Averaging. The FCC averages occupational exposure over 6 minutes and public exposure over 30. ICNIRP averages whole-body exposure over 30 minutes for both groups and keeps a separate 6-minute table for local exposure.
- Range covered. The FCC table runs from 0.3 to 100 000 MHz. ICNIRP publishes no power-density level below 30 MHz, where compliance is shown against the E- and H-field reference levels instead, and it continues to 300 GHz.
FCC values from 47 CFR § 1.1310, Table 1, as amended by 85 FR 18145 (2020). ICNIRP values from the 2020 guidelines, Table 5, whole body, averaged over 30 minutes.
How it works
- 01
Work out the radiated power
Add the antenna gain to the power reaching the antenna: EIRP = P · 10G/10. 100 W into a 6 dBi antenna radiates 398 W along the main beam, and it is the main beam that sets the safety distance.
- 02
Average over the duty cycle
Limits are averaged over 6 or 30 minutes, so a transmitter keyed for only part of that window is judged on its average power. A 50 % duty cycle halves the power density and shortens the distance by a factor of √2. A pulse radar keyed 0.1 % of the time sits three orders of magnitude below its peak, and a rotating antenna divides what is left again by 360/beamwidth, because the main lobe only sweeps past. Both factors are in the form above.
- 03
Look up the limit for your frequency
The permitted power density changes with frequency. Both the FCC and ICNIRP are strictest between roughly 30 and 300 MHz, where a standing adult is close to whole-body resonance and absorbs the most energy.
- 04
Solve for the distance
Set the far-field power density equal to the limit and solve for the distance: d = R · EIRP / (4π · Slim) . That is the closest anyone may stand in the main beam.
- 05
Sanity-check the geometry
The formula only holds a few wavelengths out from the antenna. Add the reflection factor where ground or a roof can throw the wave back, and remember that the vertical pattern usually puts far less than the main-beam gain onto the ground.
Formulas
- S — power density, W/m²
- P — time-averaged power at the antenna input, W
- G — antenna gain toward the point of interest, linear (G = 10GdBi/10)
- d — distance from the antenna, m
- R — ground-reflection factor (1, 2.56 or 4)
- Slim — power density permitted by the limit set, W/m²
- 1 mW/cm² = 10 W/m²
Worked example
- EIRP = 100 · 106/10 = 398 W
- FCC general population at 146 MHz: Slim = 0.2 mW/cm2 = 2 W/m2
- d = 398 / (4π · 2) = 3.98 m
- FCC occupational: Slim = 1.0 mW/cm2 → d = 1.78 m
- with the 2.56 ground-reflection factor: 3.98 · 1.6 = 6.37 m
FAQ
- How far do I have to stay from a transmitting antenna?
- Far enough that the power density drops below the limit for your frequency. For 100 W into a 6 dBi antenna at 146 MHz that is 3.98 m for the general public and 1.78 m for trained workers, in free space and on the main beam. Double the power and the distance grows by only √2.
- Does this calculation hold close to the antenna?
- No. The 1/d² model is a far-field model. It needs a distance of at least a few wavelengths, and for a large aperture of size D at least the Rayleigh distance 2·D2/λ. Nearer than that, the field has to be measured or modelled in the near field, and the number here can be optimistic.
- Would a radar not break these limits instantly?
- Its peak does, its time average does not, and the limits are written against the average. Take a 25 kW pulse radar at 3 GHz with 1 µs pulses at 1 kHz, which is a 0.1 % duty cycle and 25 W on average, feeding a 30 dBi antenna. With the beam parked on you the boundary sits at 14.1 m. Let the antenna turn and its 1.5° beam points your way for 1.5/360 of every revolution, which divides the exposure by 240 and pulls the boundary in to 0.91 m. A 1 MW air-traffic radar on a 34 dBi antenna works out at 141 m with the beam stopped and 9.1 m once it rotates. That is why such sites still have fences and interlocks, since the rotation can be halted for maintenance, and it is also why nobody has to stand 141 m from a working one. Set the antenna to fixed for anything that points at one spot, and to rotating with its beamwidth for anything that sweeps.
- Should I enter ERP or EIRP?
- Neither. Enter the power actually delivered to the antenna and its gain in dBi. The calculator forms the EIRP itself. If your figure is ERP, referenced to a dipole, multiply it by 1.64 to get EIRP, or add 2.15 dB to a gain given in dBd.
- Why do exposure limits depend on frequency?
- Because the human body absorbs radio energy unevenly. A standing adult is close to whole-body resonance between roughly 30 and 300 MHz, so the same power density heats tissue more there than at 2.4 GHz. Both limit tables are at their strictest in that band and relax on either side.
- Are the FCC or ICNIRP limits the ones that apply to me?
- That depends on where the station is. The FCC table applies in the United States. ICNIRP is the basis for the EU recommendation and for many national rules. Germany implements its own requirements through the BEMFV, and Switzerland adds installation limits under the NISV. Check the rule that applies to your site. This calculator is guidance, not legal advice.
Exposure distance is only half of a siting decision. Waveshed puts the same antenna on real terrain and shows where its signal actually lands, free in your browser.
Model the site on the map →Related guides
- Antenna patterns & the sensor panel — the vertical pattern decides how much of the main beam ever reaches head height
- Plan radio coverage (RF / ITM) — the same power, gain and height, seen as coverage instead of exposure
Sources & further reading
- 47 CFR § 1.1310 — Radiofrequency radiation exposure limits ↗ — the FCC maximum permissible exposure table used here, current text on eCFR
- FCC OET Bulletin 65 — Evaluating Compliance with FCC Guidelines for Human Exposure to Radiofrequency Electromagnetic Fields ↗ — prediction equations, far-field caveats, the 2.56 ground-reflection factor, and Equation (2) on p. 11, the time-averaging rule the rotating-antenna factor follows from
- ICNIRP Guidelines for Limiting Exposure to Electromagnetic Fields (100 kHz to 300 GHz), 2020 ↗ — the publication page for the 2020 guidelines, with the FAQ and the translations
- ICNIRP 2020 guidelines, full text (Health Phys 118(5):483–524, PDF) ↗ — Table 5 holds the whole-body reference levels, averaged over 30 minutes, used here
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