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Wi-Fi Link Budget & Free-Space Path Loss Calculator

Calculate received signal strength (RSSI), free-space path loss (FSPL), structural obstacle attenuation, and RF fade margins across 2.4 GHz, 5 GHz, and 6 GHz Wi-Fi channels.

Wi-Fi Frequency BandDistance Between AP and Client

AP Transmit Power (dBm)AP Antenna Gain (dBi)Client Device Antenna Gain (dBi)Obstacle / Wall AttenuationTarget Receiver Sensitivity Threshold

Select your RF parameters above and click Calculate RF Link Budget.

How the RF Link Budget & Free-Space Path Loss Formula Works

An RF Link Budget accounts for all gains and losses from the transmitter (Access Point) through the medium (air and building materials) to the receiver (laptop or smartphone):

RSSI (dBm) = P_TX + G_TX - L_TX - FSPL - L_OBS + G_RX - L_RX

Where:

P_TX (Transmit Power): Output power of the radio transmitter, typically +18 to +24 dBm (63 mW to 250 mW) on consumer routers.
G_TX / G_RX (Antenna Gain): Passive gain provided by directional or omnidirectional antenna design in dBi.
FSPL (Free-Space Path Loss): Theoretical attenuation of an electromagnetic wave travelling through vacuum or clean air: FSPL (dB) = 20·log10(d) + 20·log10(f) - 27.55 (where d is in meters and f is in MHz).
L_OBS (Obstacle Attenuation): Real-world signal absorption caused by interior drywall (-3 dB), solid wood doors (-6 dB), brick (-12 dB), and reinforced concrete (-18 dB).
Fade Margin: The critical buffer between your actual Received Signal Strength Indicator (RSSI) and the receiver sensitivity threshold. A minimum fade margin of +10 dB to +15 dB is required to absorb transient RF interference, moving human bodies, and multipath fading without dropping packets.

Signal Strength (RSSI) & Wi-Fi Modulation Quality Reference

Signal Strength (RSSI)	SNR Margin	Supported Modulation	Typical Throughput	Link Stability
`-45 dBm to -55 dBm`	≥ 40 dB	4096-QAM (MCS 12–13)	1,000–1,800+ Mbps	Flawless (Optimal Proximity)
`-56 dBm to -65 dBm`	≥ 30 dB	1024-QAM (MCS 10–11)	700–1,100 Mbps	Excellent (Gigabit Class)
`-66 dBm to -72 dBm`	≥ 22 dB	256-QAM (MCS 8–9)	350–650 Mbps	Good (Reliable HD/4K)
`-73 dBm to -78 dBm`	≥ 15 dB	64-QAM (MCS 5–7)	120–300 Mbps	Fair (Web & Streaming)
`-79 dBm to -84 dBm`	≥ 8 dB	QPSK / 16-QAM (MCS 1–4)	25–80 Mbps	Marginal (Roaming Border)
`≤ -85 dBm`	≤ 5 dB	BPSK (MCS 0) / Disconnect	< 10 Mbps	Unusable (High Packet Loss)