Walkie-talkie range calculator
Two walkie-talkies rarely reach the distance printed on the box. This calculator estimates how far a pair of handhelds really talks, from how high you hold them, how much power they put out and what stands between you. It works out three limits, then takes the smallest as the practical range.
Starts on your own numbers, pre-filled with a typical licence-exempt handheld. Pick a service to load the frequency and power its rules allow.
= 27.0 dBm · ERP, the radiated figure the rules cap. EIRP is 2.15 dB above it.
A preset sets this for you. It decides whether the 2.15 dB dipole step is added.
Above the ground you are standing on. 1.6 m is a radio held at chest height. Standing on a ridge above the ground between you acts like a much greater height.
A flat allowance added to the model. It is a coarse class, not a measurement of your trees.
Leave at 0 for a stock antenna. A short rubber duck is often −3 dBi.
−118 dBm is a conservative 12 dB SINAD figure for a consumer handheld. Amateur sets do better: the Icom IC-V80 is specified at 0.14 µV, about −124 dBm. A less negative number means a deafer radio.
Headroom for a body in the way, a wet forest or a bad moment. 15 dB is a sensible minimum for speech you can rely on.
Above is a side view: the two of you stand at the ends of your shared radio horizon, on the curve of the Earth, with the vertical scale exaggerated. The bar under the ground is that horizon, and its amber part is how far the signal really gets. Below, the same three limits as bars on a logarithmic distance scale, the binding one in amber. Power, antennas, sensitivity and surroundings move the amber marker and the lower two bars; only the two heights move the figures and the curve.
All three limits assume smooth, level ground and a standard atmosphere. The surroundings setting is a flat 0, 10 or 20 dB allowance for clutter, not a measurement of your trees, and real vegetation and buildings vary far more widely than that. Terrain overrides the lot.
Where the preset numbers come from
| Radio | Frequency | Power | Source |
|---|---|---|---|
| PMR446 | 446.1 MHz | 0.5 W ERP | ECC/DEC/(15)05 ↗ |
| FRS | 462.6 MHz | 2 W ERP | 47 CFR 95.563, 95.567 ↗ |
| GMRS | 462.6125 MHz | 5 W ERP | 47 CFR 95.1763, 95.1767 ↗ |
| 2 m (VHF) | 146 MHz | 5 W at the socket | Kenwood TH-D75A ↗ |
| 70 cm (UHF) | 440 MHz | 5 W at the socket | Kenwood TH-D75A ↗ |
Every figure comes from the document linked beside it, last checked on 2026-08-18. The presets are a selection of the common services, not a full catalogue: marine VHF, business radio and national services are left out.
How it works
- 01
Pick the radio, not the marketing
The preset fills in the frequency and the power the service actually allows. PMR446 handhelds radiate 0.5 W ERP, FRS 2 W on most of its channels, GMRS handhelds 5 W, and an amateur handheld puts out about 5 W at the antenna socket. The kilometre figure on the packaging is not an input.
- 02
Turn the power into EIRP
ERP is referred to a half-wave dipole and EIRP to an isotropic one, and the two differ by 2.15 dB. The range formulas want EIRP, so 0.5 W ERP becomes 27.0 + 2.15 = 29.1 dBm. Any antenna gain you add sits on top of that.
- 03
Work out the loss you can afford
Everything the far end needs comes off what you radiate: Lmax = EIRP + Grx − Srx − M − Lenv. A radio that hears −118 dBm, 15 dB of fade margin and open ground leave 132.1 dB of path loss to spend.
- 04
Compare three limits
Free space, L = 32.45 + 20·log10 dkm + 20·log10 fMHz, is the ceiling with nothing near the path. The two-ray model adds the ground reflection, which cancels most of the direct ray, so loss grows as 40·log10 d instead. The radio horizon, 4.12·(h1 + h2) km, is pure geometry and ignores power completely.
- 05
Take the smallest, then look at the map
The practical range is whichever limit runs out first. For two people on foot that is almost always the ground reflection, a few kilometres at best. One hill between you overrides all three, and none of these formulas knows the hill is there.
Formulas
- EIRP — radiated power, dBm (ERP + 2.15 dB)
- Grx — receiving antenna gain, dBi
- Srx — receiver sensitivity, dBm
- M — fade margin, dB
- Lenv — flat allowance for the surroundings, dB
- d — range, m
- h1, h2 — antenna heights above ground, m
- holds beyond the breakpoint distance db = 4·h1·h2 / λ
- dh — horizon distance, km
- h1, h2 — antenna heights above ground, m
Worked example
- EIRP = 0.5 W ERP = 27.0 dBm + 2.15 dB = 29.1 dBm
- Lmax = 29.1 + 0 − (−118) − 15 − 0 = 132.1 dB
- Radio horizon: 4.12 · (1.6 + 1.6) = 10.4 km
- Two-ray: 40·log10 d = 132.1 + 4.08 + 4.08 → d = 3 218 m
- Free space: 132.1 dB at 446.1 MHz → 216 km, a number nobody has ever measured
- → practical range ≈ 3.2 km, and one hill can halve it
FAQ
- Why does the box say 10 km when I get two?
- That figure is measured with nothing in the way at all, typically summit to summit or across open water. Held in the hand on level ground, a pair loses most of its signal to the ground reflection and manages two to five kilometres in the open, or a few hundred metres in a forest or a town.
- What does a hill between us do?
- It ends the conversation long before any of these numbers apply. All three limits assume smooth ground. A ridge that blocks the sight line adds diffraction loss that easily runs to tens of decibels, and because loss grows as 40·log10 d close to the ground, 20 dB of it cuts the range by a factor of three. No formula on this page knows the ridge is there, so check the terrain profile.
- Does more power give more range?
- Barely. Doubling the transmit power adds 3 dB, which close to the ground stretches the range by about 19 %. Ten times the power buys about 78 %. A 5 W radio does not reach ten times as far as a 0.5 W one. It reaches roughly twice as far.
- Why does holding the radio higher help more than turning up the power?
- Because height enters the ground-reflection formula twice, once for each end. Raising one radio from 1.6 m to 3.2 m adds 6 dB, exactly what quadrupling the transmit power would give. Raise both and the range doubles. A wall, a car roof or a small rise is the cheapest range upgrade there is.
- Which service may I use, and can I fit a bigger antenna?
- PMR446 is licence-exempt across most of Europe at 0.5 W ERP with a fixed antenna, so a bigger aerial is not an option. FRS is licence-free in the United States and Canada, also with a non-removable antenna. GMRS needs an individual FCC licence and does allow external antennas. The amateur bands need an amateur licence. Check your national regulator before you rely on any of this.
These numbers assume the ground between you is smooth. It never is. Waveshed draws the sight line over real elevation data, so you can see whether the ridge in the way actually blocks you.
Check your route on the map →Related guides
- LOS vs RF — which analysis do you need? — when a clear sight line answers the question and when it does not
- Heights: AGL vs AMSL — the height that counts is the one above the ground you are standing on
- Antenna height vs transmit power — why a metre of height beats a watt of power, worked through with the same formulas
Sources & further reading
- ITU-R Recommendation P.525 — Calculation of free-space attenuation ↗ — the free-space limit shown on this page
- ECC/DEC/(15)05 — PMR 446 in 446.0–446.2 MHz (CEPT ECO documentation database) ↗ — the decision itself: 500 mW ERP, integral antenna only, no individual licence
- ETSI EN 303 405 V1.1.1 — Analogue and Digital PMR446 Equipment ↗ — the harmonised standard PMR446 handhelds are tested against, with the channel plan (PDF)
- 47 CFR Part 95 — Personal Radio Services (eCFR) ↗ — § 95.563 and § 95.567 give the FRS channels and power, § 95.1763 and § 95.1767 the GMRS ones
- Kenwood TH-D75A specifications ↗ — a named 144/220/430 MHz handheld behind the 5 W figure of the amateur presets
- Icom IC-V80 specifications ↗ — receiver sensitivity 0.14 µV at 12 dB SINAD, the datasheet behind the sensitivity default
- Two-ray ground-reflection model — Wikipedia ↗ — derivation of the 40·log10 d law behind the ground limit
Related tools
Radio horizon calculator
How far a signal reaches over smooth earth, from antenna height.
Link budget calculator
Received power and fade margin from TX power, gains, losses and path loss.
How far can you see? Horizon distance calculator
Distance to the horizon from any height, and how much of a distant peak or ship the curve hides.
LoRa / Meshtastic range calculator
Maximum link distance from spreading factor, TX power, antennas and heights: free space, ground and horizon limits.