Free Space Path Loss Calculator
Rx power (dBm) = Tx power (fixed 0 dBm) + TX gain + RX gain – FSPL.
What is Free Space Path Loss (FSPL)?
Free Space Path Loss (FSPL) represents the reduction in signal strength as a radio wave travels through free space without obstacles. It is a fundamental concept in RF engineering, microwave communication, satellite links, LTE, and 5G network planning.
FSPL depends only on two variables:
- Distance between transmitter and receiver
- Operating frequency
As distance or frequency increases, the signal attenuation increases logarithmically.
FSPL Formula (Free Space Path Loss Equation)
The standard FSPL formula in decibels (dB) is:
- d = distance in kilometers (km)
- f = frequency in megahertz (MHz)
- 32.44 = constant for km and MHz units
If distance is used in meters or frequency in GHz, the constant value changes accordingly.
Should Distance Be in km or m for FSPL?
In the standard engineering formula, distance must be entered in kilometers (km) and frequency in MHz. If you use meters or GHz, you must adjust the constant value in the formula.
For example:
- Distance in meters → constant becomes 147.55
- Frequency in GHz → adjust formula accordingly
Your calculator automatically converts units internally to ensure accurate results.
FSPL Example Calculation
Let’s calculate the path loss for:
- Distance = 5 km
- Frequency = 2400 MHz
Applying the formula:
FSPL ≈ 114 dB
If transmitter power is 0 dBm and both antennas have 2 dBi gain:
Received Power = 0 + 2 + 2 − 114 ≈ −110 dBm
Why FSPL is Important in RF and Wireless Communication
- Microwave link budget planning
- LTE and 5G network design
- Satellite communication systems
- WiFi coverage analysis
- RF propagation modeling
Engineers use FSPL calculations to estimate signal coverage, optimize antenna placement, and predict received signal strength.
FSPL vs Link Budget
FSPL represents only the free-space attenuation component. A complete link budget also includes:
- Transmitter power (dBm)
- Antenna gains (dBi)
- Cable losses
- Connector losses
- Fade margin
FAQ on Calculator
FSPL (Free Space Path Loss) is the signal attenuation that occurs when a radio wave propagates through free space without obstacles.
FSPL is calculated using: 20 log₁₀(d) + 20 log₁₀(f) + 32.44 where distance is in km and frequency in MHz.
No. FSPL depends only on distance and frequency. Antenna gains are included separately in link budget calculations.
Yes. Path loss increases as frequency increases.