Marine VHF Range Calculator
Last updated: September 2026
How far can a marine VHF radio transmit?
Marine VHF is line-of-sight, so range is set by the radio horizon: about 1.23 × (√h₁ + √h₂) nautical miles, where h₁ and h₂ are the two antenna heights in feet. A typical 25 W fixed-mount radio with an 8 ft antenna on a center console reaches roughly 6–10 nautical miles to a similar boat and 20 nautical miles or more to a tall Coast Guard tower. Antenna gain sharpens the signal within that horizon; it does not reach past it.
Move the sliders to see your realistic range — and why antenna height beats wattage every time.
Antenna tip height: mount height + antenna length. A center console T-top with an 8ft antenna ≈ 16ft.
Another boat ≈ 10–15ft. Coast Guard shore towers ≈ 100–300ft.
How the Radio Horizon Formula Works
VHF signals at 156–162 MHz travel in nearly straight lines and do not follow the curvature of the earth. Your effective range is the distance to your radio horizon plus the distance to the other station's horizon:
The 1.23 coefficient includes standard atmospheric refraction, which bends VHF slightly beyond the visual horizon. Real-world results vary with sea state, atmospheric ducting, and — critically — installation quality: corroded connectors and cheap coax can cut your effective radiated power in half.
Example Ranges
| Scenario | Antenna Heights | Approx. Range |
|---|---|---|
| Two center consoles | 12 ft / 12 ft | 8.5 NM |
| Center console to sportfish flybridge | 12 ft / 30 ft | 11 NM |
| Boat to Coast Guard shore station | 12 ft / 100 ft | 16.5 NM |
| Sailboat masthead to shore station | 50 ft / 100 ft | 21 NM |
Marine VHF antenna length and range chart
Antenna length sets gain and, more importantly, where the antenna ends up mounted. This chart uses the tip height each class typically reaches on the boats it is built for. “Horizon” is that antenna's own radio horizon (the other station at sea level); “To a 30 ft coast antenna” adds the 6.7 NM horizon of a typical marina or harbormaster antenna. Add your own horizon to another boat's to get boat-to-boat range.
| Antenna length | Typical gain | Typical tip height | Horizon | To a 30 ft coast antenna | Best for | Scout models |
|---|---|---|---|---|---|---|
| 3 ft | 3 dB | ~8 ft (rail or cabin top, small boat) | 3.5 NM | ~10 NM | Dinghies, skiffs, jon boats, RIBs, backup antenna | KS-21 · KS-23A |
| 4 ft | 3 dB | ~10 ft (console or gunwale mount) | 3.9 NM | ~10.6 NM | Bay boats and center consoles under 24 ft that pitch and roll | KS-41 |
| 5 ft | 3 dB | ~12 ft (console or hardtop edge) | 4.3 NM | ~11 NM | Runabouts, pontoons and cuddy cabins that want a little more reach | KS-22 · KS-50 |
| 8 ft | 6 dB | ~16 ft (T-top, hardtop or flybridge) | 4.9 NM | ~11.6 NM | Offshore center consoles, sportfish, cruisers and trawlers over 24 ft | KS-42 · KS-43 |
| Masthead / sailboat | 3 dB | ~50 ft (top of mast) | 8.7 NM | ~15.4 NM | Sailboats: the tallest mount on the water, so a short 3 dB antenna wins | Windex VHF 90 · KM-22 BS |
Horizon figures are 1.23 × √(tip height in feet), rounded. Mount the same antenna higher and the numbers move up with it — which is the whole point of the next section.
Why antenna height matters more than gain
Height is the only variable in the range formula. Doubling the tip height of your antenna from 8 ft to 16 ft moves your radio horizon from 3.5 NM to 4.9 NM, and that gain shows up on every single contact. Gain does not appear in the formula at all.
What gain does is shape the signal. A 6 dB antenna flattens its radiation pattern into a disc aimed at the horizon, so a station at the edge of range hears you more clearly than it would from a 3 dB antenna at the same height. On a small boat that rolls, that flat disc tips above and below the horizon and drops the contact, which is why the 3 dB pattern is the safer choice under about 24 ft. Our gain explainer covers the trade-off in detail.
Practical order of operations: mount as high as the boat allows, pick the gain that suits the hull's motion, then protect the result with good coax and a clean PL-259. If you are weighing the jump to 8 ft, see what an 8 ft antenna really adds.
Once you know the range you need, the next question is which antenna delivers it on your hull. Our ranked guide to the best marine antennas names one pick per boat size, from a 4 ft 3 dB for a small centre console to an 8 ft 6 dB for a hardtop, with the gain and mounting height that each one assumes.
Antennas for maximum range
Height first, then gain: an 8 ft 6 dB antenna on a T-top or hardtop is the practical range ceiling for most powerboats.
VHF range questions, answered
How far can a VHF radio transmit?
A 25W fixed-mount marine VHF with an 8ft antenna on a center console typically reaches about 6–10 nautical miles to a similar boat and 20 nautical miles or more to a tall Coast Guard tower. VHF is line-of-sight, so the limit is the radio horizon set by antenna height, not transmitter power.
What is VHF range in nautical miles?
Each station’s radio horizon in nautical miles is about 1.23 × √(antenna height in feet). Add both horizons for the total range: an antenna at 16ft (4.9 NM) talking to a 30ft coast antenna (6.7 NM) gives roughly 11.6 NM; two boats at 16ft each give about 9.8 NM.
Does a longer antenna increase VHF range?
Only indirectly. A longer 8ft antenna has more gain (6dB vs 3dB), which concentrates signal toward the horizon and improves clarity at the edge of range, and it usually mounts higher, which is what actually extends the horizon. Length alone does not push a signal past the curvature of the earth.
How far can a handheld VHF reach?
A handheld VHF (1W or 5W) held at about 5ft above the water has a radio horizon of roughly 2.75 NM, so expect about 2–5 nautical miles boat-to-boat and 8–10 NM to a tall coast station. Its short rubber antenna and low height, not its wattage, are what limit it.
How is VHF radio range calculated?
VHF is line-of-sight, so range is governed by the radio horizon: approximately 1.23 × √(antenna height in feet) in nautical miles for each station. Total range is the sum of both stations’ horizons. Two boats with 12ft antennas can communicate roughly 8.5 nautical miles; a boat and a 100ft Coast Guard tower roughly 16.5 nautical miles.
Does more wattage increase VHF range?
Not beyond the horizon. Once terrain and curvature block line-of-sight, no legal wattage (25W max marine) reaches farther. Antenna height extends the horizon; antenna gain concentrates the signal within it. Money spent on a taller mount and a quality antenna outperforms any radio upgrade.
Should I choose a 3dB or 6dB antenna?
Boats under about 24ft that pitch and roll should use a 3dB antenna (like the 4ft Scout KS-41 or 5ft KS-22) whose wider radiation pattern stays on the horizon in a seaway. Larger, more stable boats benefit from a 6dB antenna (8ft Scout KS-42 or KS-43) that focuses more energy toward the horizon for maximum range.