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Free Space Path Loss Calculator
Calculators / Free Space Path Loss
Free Space Path Loss
Calculator
Calculate FSPL — the fundamental signal attenuation of a radio wave travelling through free space. Essential for RF communication link design, antenna system design, and wireless network planning. Uses the Friis transmission equation.
TX
FSPL
RX
⚙ FSPL Engine
λ = — cm in free space
Free-space propagation distance
20 dBm = 100 mW
dB
Enter known FSPL when solving for d or f
dBi
0 dBi = isotropic, dipole = 2.15 dBi
dBi
0 dBi = isotropic antenna at receiver
Additional Losses
dB
dB
dBm
Used to calculate link margin
Calculated Results
Free Space Path Loss (FSPL)
—dB
Path loss severity
—
Received Power (Pr)—
Link Margin—
EIRP—
Max Range—
FSPL (dB)—
Total path loss—
Wavelength (λ)—
Frequency (f)—
Distance (d)—
Link Status—
Enter frequency and distance above to calculate.
📖 Theory
Free Space Path Loss is the attenuation of an RF signal as it spreads out from a transmitter in free space — with no obstructions, reflections, or absorption. It increases with both distance and frequency.
FSPL Formula (dB)
FSPL = 20·log(d_km) + 20·log(f_GHz) + 92.44
d in km, f in GHz. Classic telecom form.
Friis Form (linear)
FSPL = (4πd/λ)²
Pr = Pt·Gt·Gr·(λ/4πd)²
Key Rules
Double distance → +6 dB FSPL
Double frequency → +6 dB FSPL
×10 distance → +20 dB FSPL
×10 frequency → +20 dB FSPL
📊 FSPL Visualiser
Live Charts
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◉ FSPL vs Distance & vs Frequency
Chart
Frequency
2.4 GHz
0.130 GHz
Max Dist
100 km
FSPL (dB) vs Distance
ℹ
Link Design Insights
Enter frequency and distance to see path loss insights.
Common Applications
RF Communication Links
Calculate path loss for any point-to-point radio link — cellular, microwave backhaul, ISM band, and licensed bands.
Antenna System Design
Determine required antenna gain, transmit power, and receiver sensitivity to close a radio link over a given distance.
Wireless Network Planning
WiFi cell sizing, LoRa range estimation, and 5G coverage planning all start with free-space path loss as the baseline.
Satellite Links
GPS, LEO, and GEO satellite link budgets. Free-space path loss dominates over thousands of kilometres in space.
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