Tower Horizon Calculator v2.0 — Waypoint Utility Web

Inputs Heights in feet

Location coordinates, U.S. street address or ZIP

Coordinates are exact; street addresses are approximate Census geocodes; ZIP codes use an approximate geographic center. Confirm the location on the map before planning a radio path.

Enter a location and select Locate, or use an FCC registration below.

FCC antenna registration (ASRN)

Optional, 7 digits; FCC record snapshot.

Enter an ASRN for an FCC lookup, or use manual inputs below.

Base elevation ft AMSL

Registered tower height ft AGL

Radiation center ft AGL

Receiver height ft AGL

AMSL = above mean sea level. AGL = above ground level. Base elevation affects only the AMSL result.

Automatic estimate: tower top minus 8 m (26.2467 ft), with a minimum of 0 ft.

Results Updated as you type

Standard radio horizon—k = 4/3 effective Earth

Geometric horizon—k = 1, no refraction

Theoretical area—Circle using the radio-horizon radius

Radiation center AMSL—Enter base elevation to calculate

Estimated populationNot availablePlaceholder — Census data not connected

Population densityNot availablePlaceholder — people per square mile

USGS 3DEP — Terrain & Line-of-Sight Analysis BETA

USGS elevations are interpolated bare-earth estimates. This models terrain visibility, not received signal strength. Use actual antenna center AGL when known. FCC lookup or coordinate entry populates the transmitter location.

1. Transmitter location & elevation

TX latitude

TX longitude

Load elevation to populate the transmitter results.

Ground elevationNot loaded

Antenna center AMSL—

2. Point-to-point receiving location

Street address (U.S. Census geocoder)

RX latitude

RX longitude

Receiver antenna height ft AGL (above ground level)

Mirrors the Receiver height input in the calculator above. Changing either field updates the other automatically.

Or click the map to set the receiver location.

Effective Earth-radius factor

Terrain samples per path

Select a receiver and run the path analysis.

Terrain path—

Minimum clearance—

Additional height to clear sampled terrain (either endpoint)—

POINT-TO-POINT REPORT

One-page Letter report with the two sites, path distance, compass bearing, geometric clearance, elevation profile, and one 30° sector centered on the link. The sector is visual context, not an antenna beamwidth or predicted coverage.

Elevation cross-section

3. 360° terrain-visibility map

PROCESSING NOTICE | USGS 3DEP

This calculation uses the USGS 3DEP ImageServer. Multipoint sampling requests 48 preselected geographic positions per radial in one query. Results can still take a minute or longer, depending on USGS response times.

Fastest uncached full scan: 12 USGS queries (12 bearings × 48 requested positions = 576 terrain positions), in four chunks of three. Full 24- or 36-bearing scans require 24 or 36 queries. Repeated scans may reuse cached results, and missing data may require extra elevation lookups. Multipoint requests are preferred, with legacy polyline fallback when the route is unavailable. Unverifiable terrain remains gray.

Compass bearings

Map background

Coarse approximation using 40 distance rings per bearing, bounded by the standard radio horizon (maximum 120 mi). This is not an FCC service contour. Unknown sample regions are shaded gray.

Estimated terrain-visible area—

Run the 360° analysis to update the map.

EXPORT & REPORTING Current calculation / current map view

Run a terrain scan to enable CSV and KML exports. PDF reports identify any incomplete results.

Map legend: Green = mostly terrain-clear Red = mostly terrain-blocked Gray = incomplete terrain data Blue dashed = theoretical horizon. Estimates reflect sampled paths and elevations only.

Method & assumptions

Distance from both antenna heights

Heights hₜ and hᵣ are in feet AGL; distances are in miles.

Radio: d ≈ 1.415 × (√hₜ + √hᵣ)
Geometric: d ≈ 1.225 × (√hₜ + √hᵣ)

The calculation uses √(2kRh) for each endpoint, R = 6,371 km, and k = 4/3 for a standard refracting atmosphere or k = 1 for geometric line of sight. Coefficients shown are rounded; calculations use the constants directly. See ITU horizon geometry.

A useful first approximation

Area = πd², a theoretical circle in square miles. Radiation center AMSL = base elevation AMSL + radiation center AGL.

Assumes a smooth Earth and similar ground elevations at both ends. These heights are not HAAT (height above average terrain). Base elevation is not added to the horizon height.

The 8 m antenna setback is a rough convenience estimate, not FCC antenna data. Enter the actual radiation center when known. Geocoded addresses and ZIP centers are approximations, not surveyed tower sites. Population and density are reserved for a future data integration.

Engineering reality check: The Earth keeps curving, no matter how inconvenient that is for the spreadsheet. And a clear terrain path is still not a guarantee that the RF signal will cooperate.

Sources & reference desk

RabbitEars is linked as a courtesy. This independent calculator is not affiliated with or endorsed by RabbitEars, the FCC, the Census Bureau, or USGS. Educational estimates only.