| TX Power | {{ txPower }} dBm |
| TX Ant. Gain | {{ txGain }} dBi |
| TX Cable Loss | -{{ txCableLoss }} dB |
| RX Ant. Gain | {{ rxGain }} dBi |
| RX Cable Loss | -{{ rxCableLoss }} dB |
| Additional Loss | -{{ additionalLoss }} dB |
| Calculated FSPL | {{ fspl.toFixed(2) }} dB |
| Received Power | {{ rxPower.toFixed(2) }} dBm |
Free-space path loss (FSPL) describes how radio-frequency energy spreads as it travels through unobstructed air. Understanding FSPL lets you predict how strongly a signal arrives after passing a given distance at a chosen frequency, a cornerstone of reliable wireless design.
This calculator couples a reactive engine with an interactive charting layer to model link budgets in real time. Enter frequency, separation and hardware gains or losses; the algorithm instantly returns FSPL and received signal strength indicator (RSSI) while visualising distance and frequency sweeps.
Use it when planning Wi-Fi, IoT or microwave links to confirm margins before deployment. Results assume clear line-of-sight; walls, foliage or rainfall add extra attenuation.
The tool applies the Friis transmission equation under free-space conditions, combining logarithmic path-loss with antenna and feed-line terms. Computation is entirely client-side for privacy and near-instant updates.
| Symbol | Description | Typical Range |
|---|---|---|
d | Line-of-sight distance | 1 m – 100 km |
f | Carrier frequency | 100 MHz – 60 GHz |
PTX | Transmitter power (dBm) | -30 – +30 dBm |
GTX/RX | Antenna gain (dBi) | -5 – +24 dBi |
LC | Cable / other loss (dB) | 0 – 20 dB |
| RSSI (dBm) | Link Quality |
|---|---|
| > -65 | Excellent |
| -65 … -80 | Good |
| -80 … -100 | Marginal |
| < -100 | Unreliable |
All maths use native floating-point operations; complexity is O(n) for sweeps where n ≤ 60, providing fluid updates even on low-power devices.
Follow this workflow to predict signal strength quickly.
Frequency accepts megahertz or gigahertz; distance accepts metres or kilometres. Internal maths normalises to MHz and km.
A zero or negative frequency or distance produces an undefined logarithm, yielding Not-a-Number until corrected.
No. All calculations run locally in your browser; parameters persist only in the address bar for sharing.
The model matches theoretical free-space loss within 0.1 dB. Real-world conditions introduce extra attenuation not estimated here.
This tool covers line-of-sight scenarios only. For multipath or urban settings, apply terrain-specific models externally.