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Calcimator

Emergency Communication Range Calculator

Estimate two-way radio range for emergency communications based on power, antenna height, terrain, and frequency band.

Inputs

Results

Effective range (mi)

3.55

Line-of-sight range (mi)6.96
Coverage area (sq mi)39.54
HF skip range (mi)0
Range w/ 100ft antenna (mi)9.02
Repeaters for 100 sq mi3
Est. battery life (hrs)30.3
How to Use This Calculator
  1. Enter your Transmit Power (watts) and Antenna Height (ft).
  2. Input the Remote Antenna Height (ft) at the other end of the link.
  3. Select Terrain Type (flat, rolling, hilly, mountainous, or urban).
  4. Choose the Radio Band (VHF, UHF, 700 MHz, or 800 MHz).
  5. Review Effective Range (miles) and Line-of-Sight Range to plan repeater placement.

How the result changes with Transmit power (watts)

Transmit power (watts)Effective range (mi)
105.02
359.39
6512.79
9015.05

What each input means

Transmit power (watts)
Radio transmit power in watts (FRS: 0.5W, GMRS: 1-50W, VHF ham: 5-50W).
Your antenna height (ft)
Height of your antenna above ground (handheld ~6 ft, vehicle ~10 ft, rooftop ~30 ft).
Remote antenna height (ft)
Height of the other station's antenna.
Terrain type (0-4)
0=Flat/open, 1=Suburban, 2=Urban, 3=Dense forest, 4=Mountains.
Radio band (0-3)
0=FRS (UHF), 1=GMRS, 2=VHF (ham/CERT), 3=HF (ham, long-range).

What each result means

Effective range (mi)
Estimated usable communication range accounting for terrain and power.
Line-of-sight range (mi)
Maximum theoretical range based on antenna heights (no obstructions).
Coverage area (sq mi)
Circular coverage area from your position.
HF skip range (mi)
Ionospheric skip range (HF band only, conditions-dependent).
Range w/ 100ft antenna (mi)
Range if your antenna were elevated to 100 ft (repeater/tower height).
Repeaters for 100 sq mi
Number of repeaters needed to cover a 100 sq mi area.
Est. battery life (hrs)
Estimated battery life with typical 5% TX, 5% RX, 90% standby duty cycle.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Transmit power (watts) = 5, Your antenna height (ft) = 6, Remote antenna height (ft) = 6, Terrain type (0-4) = 1 = 5 input(s) provided
  2. Calculate Effective range
    Effective range = losRangeMiles * terrainFactor * powerFactor * bandMultiplier
    3.55 = 3.55
  3. Calculate Line-of-sight range
    Line-of-sight range = 1.42 * (sqrt(antennaHeightFt) + sqrt(remoteAntennaHeightFt))
    6.96 = 6.96
  4. Calculate Coverage area
    Coverage area = π * effectiveRangeMiles * effectiveRangeMiles
    39.54 = 39.54

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