Or enter frequency manually below
MHz
Enter in MHz (2400 = 2.4 GHz)
m
Distance between transmitter and receiver
Sets path loss exponent (n)
dBm
WiFi router: 20 dBm · LTE base: 43–46 dBm
dBm
WiFi client: −70 to −90 dBm typical
Free Space Path Loss (FSPL)
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💡 Link budget tip: Received signal = Tx Power + Antenna Gains − Path Loss. For a reliable link, received signal should be at least 10 dB above receiver sensitivity. Add fade margin of 10–20 dB for outdoor links.
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Path Loss Formulas Explained
Path loss quantifies how much signal power is lost as a radio wave travels from transmitter to receiver. Two models are commonly used:
Free Space Path Loss (FSPL)
FSPL (dB) = 20×log₁₀(d) + 20×log₁₀(f) + 20×log₁₀(4π/c)
= 20×log₁₀(d) + 20×log₁₀(f) − 147.55
Where d = distance in meters, f = frequency in Hz
Simplified: FSPL (dB) = 20×log₁₀(d_km) + 20×log₁₀(f_MHz) + 32.44
Example: 2.4 GHz WiFi at 100 m → 20×log₁₀(0.1) + 20×log₁₀(2400) + 32.44 = 80 dB
Simplified: FSPL (dB) = 20×log₁₀(d_km) + 20×log₁₀(f_MHz) + 32.44
Example: 2.4 GHz WiFi at 100 m → 20×log₁₀(0.1) + 20×log₁₀(2400) + 32.44 = 80 dB
Log-Distance Path Loss Model
PL(d) = PL(d₀) + 10×n×log₁₀(d/d₀)
Where n = path loss exponent, d₀ = reference distance (1 m), PL(d₀) = FSPL at 1 m
This model accounts for real-world environments using the exponent n.
Free space: n=2 · Indoor typical: n=3–4 · Dense indoor: n=4–5
This model accounts for real-world environments using the exponent n.
Free space: n=2 · Indoor typical: n=3–4 · Dense indoor: n=4–5
Common Path Loss Exponents
| Environment | Exponent (n) | Notes |
|---|---|---|
| Free space | 2.0 | Theoretical minimum, line of sight |
| Open outdoor | 2.0–2.5 | Rural, fields, open areas |
| Suburban | 2.5–3.0 | Residential neighborhoods |
| Urban | 3.0–3.5 | Buildings, reflections, diffraction |
| Indoor open | 3.0 | Open office, warehouse |
| Indoor obstructed | 3.5–4.5 | Walls, floors, furniture |
| Dense indoor | 4.0–5.0 | Concrete walls, steel structures |
Sources & Methodology
Formulas based on ITU-R propagation models and IEEE 802.11 standard path loss models. Updated March 2026.
International Telecommunication Union recommendation for calculating free-space path loss
Path loss models and reference values for WiFi frequency bands used in this calculator
Methodology: FSPL = 20×log₁₀(d_m) + 20×log₁₀(f_Hz) − 147.55. Log-distance model: PL(d) = FSPL(1m) + 10×n×log₁₀(d). Link margin = Tx power − path loss − receiver sensitivity. Results assume isotropic antennas with 0 dBi gain. Real-world results vary with antenna gain, polarization, and local obstructions.
Last reviewed: March 2026
Frequently Asked Questions
Free space path loss (FSPL) is the signal attenuation that occurs as an electromagnetic wave travels through open space with no obstacles. It increases with both frequency and distance. FSPL doubles (adds 6 dB) every time you double the frequency, and doubles again every time you double the distance. It represents the theoretical minimum loss for any wireless link.
Higher frequencies experience more path loss. 5 GHz has roughly 6 dB more free space path loss than 2.4 GHz at the same distance. Additionally, higher frequencies have less ability to penetrate walls and obstacles — 2.4 GHz can pass through multiple walls while 5 GHz struggles after one or two. The tradeoff is that 5 GHz supports higher data rates due to wider available spectrum.
WiFi signal quality by RSSI: −30 to −50 dBm = excellent (very close to router); −50 to −60 dBm = good (reliable for all activities); −60 to −70 dBm = fair (web browsing, email); −70 to −80 dBm = weak (basic connectivity only); below −80 dBm = unusable. For video streaming you need at least −60 dBm. For VoIP calls, −67 dBm is the minimum recommended level.
A link budget is a calculation of all gains and losses in a radio link to determine if the received signal will be strong enough for reliable communication. Link budget = Tx power (dBm) + Tx antenna gain (dBi) − cable losses (dB) − path loss (dB) + Rx antenna gain (dBi) − required SNR (dB). The result tells you the link margin — how much headroom you have above the minimum required signal level.
The path loss exponent (n) describes how rapidly signal power decreases with distance. In free space n=2, meaning signal power drops as the square of distance (inverse square law). In real environments n is higher because of reflections, absorption, and diffraction. With n=4 (dense indoor), signal power drops 4× faster with distance compared to free space. Higher n means you need stronger transmit power or shorter range for reliable communication.
The Friis transmission equation calculates received power considering antenna gains: Pr = Pt + Gt + Gr − FSPL (all in dB), where Pt is transmit power, Gt is transmit antenna gain, Gr is receive antenna gain, and FSPL is free space path loss. This is the basis of all link budget calculations. Adding antenna gain directly offsets path loss — a 6 dBi antenna doubles the effective range compared to a 0 dBi isotropic antenna.
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