Free Space Path Loss Calculator
Calculate signal attenuation due to spreading in free space (FSPL).
FSPL Reference Table
| Distance | 900 MHz | 2.4 GHz | 5.8 GHz |
|---|---|---|---|
| 100 m | 71.5 dB | 80.0 dB | 87.7 dB |
| 1 km | 91.5 dB | 100.0 dB | 107.7 dB |
| 10 km | 111.5 dB | 120.0 dB | 127.7 dB |
| 100 km | 131.5 dB | 140.0 dB | 147.7 dB |
Free Space Path Loss Formula
FSPL (dB) = 20 log10(d) + 20 log10(f) + 32.44
where d = distance in km, f = frequency in MHz
where d = distance in km, f = frequency in MHz
Key Points
- FSPL assumes unobstructed line-of-sight propagation
- Doubling the distance adds 6 dB of loss
- Doubling the frequency adds 6 dB of loss
- Real-world loss is typically higher due to obstacles
When to Use FSPL
- Point-to-point wireless links
- Satellite communications
- Clear line-of-sight microwave links
- Initial link budget estimates