Calculations: Free Space Loss
The can be calculated by the formula listed below which is the transmission loss between two antennas, separated by a distance. Enter the operating frequency in MHz (2400 for 2.4 GHz, 5800 for 5.8 GHz, etc.) and the distance between the two attennas in miles.
For further information on this formula, please review the figure below.
Note: The final value represents a first order approximation and should only be used as a guide. No guarantees or warranties are implied accordingly.
Free Space Loss Example

Notes: The formula for calculating free space loss is 20 * Log10 (frequency in MHz) + 20 * Log10 (Distance in Miles)