Calculate beacon distance, RSSI, or Tx Power from any 2 inputs and convert distance between meters, cm, km, feet, yards, or miles.
Related Calculators
- Antenna dBi Range Calculator
- dBm to Range Calculator
- Receiver Sensitivity Calculator
- Link Margin Calculator
- Radio Distance Calculator
- Coupling Loss Calculator
- All Physics Calculators
Beacon Distance Formula
The beacon distance calculation uses the log-distance path loss model. This calculator uses a fixed path loss exponent of n = 2, which represents ideal free-space signal behavior.
D = 10^((Tx - RSSI)/(10*n))
RSSI = Tx - (10*n*log10(D))
Tx = RSSI + (10*n*log10(D))
- D = distance from the beacon, in meters before unit conversion
- RSSI = received signal strength indicator, in dBm
- Tx = measured power or Tx power at 1 meter, in dBm
- n = path loss exponent, fixed at 2 in this calculator
- log10 = base-10 logarithm
If you enter RSSI and Tx power, the calculator solves for distance. If you enter Tx power and distance, it solves for RSSI. If you enter RSSI and distance, it solves for Tx power. Distance values are converted to meters for the formula, then converted back to your selected unit when distance is the result.
Common Beacon Signal Reference Values
RSSI values are usually negative. A value closer to 0 means a stronger received signal.
| RSSI range | Typical meaning | Distance estimate quality |
|---|---|---|
| -30 to -50 dBm | Very strong signal, usually nearby | Better, but still affected by device orientation |
| -51 to -70 dBm | Moderate signal | Usable for rough proximity |
| -71 to -90 dBm | Weak signal | Less reliable |
| Below -90 dBm | Very weak signal | Often unstable or out of practical range |
Distance Unit Conversions Used
| Unit | Conversion to meters |
|---|---|
| Centimeters | 1 cm = 0.01 m |
| Meters | 1 m = 1 m |
| Kilometers | 1 km = 1000 m |
| Feet | 1 ft = 0.3048 m |
| Yards | 1 yd = 0.9144 m |
| Miles | 1 mi = 1609.34 m |
Example Calculations
Example 1: Calculate distance
Suppose the RSSI is -70 dBm and the Tx power is -59 dBm.
D = 10^((-59 - (-70))/(10*2))
D = 10^(11/20) = 3.5481 m
The estimated beacon distance is 3.5481 meters.
Example 2: Calculate RSSI
Suppose the Tx power is -59 dBm and the distance is 5 meters.
RSSI = -59 - (10*2*log10(5))
RSSI = -59 - 13.9794 = -72.9794 dBm
The estimated RSSI is -72.9794 dBm.
FAQs
What is Tx power in a beacon distance calculation?
Tx power, sometimes called measured power, is the expected RSSI at a reference distance of 1 meter from the beacon. For many Bluetooth beacons, this value is a negative dBm number such as -59 dBm. The distance estimate depends heavily on this value, so use the calibrated measured power for your specific beacon when possible.
Why is beacon distance only an estimate?
RSSI changes because of walls, reflections, interference, antenna direction, body blocking, and differences between phones or receivers. The formula assumes a simple signal-loss pattern. Real indoor environments rarely match that perfectly, so the result should be treated as an approximate distance, not an exact measurement.
What does the path loss exponent mean?
The path loss exponent controls how quickly signal strength drops as distance increases. This calculator uses n = 2, which represents free-space conditions. Indoor spaces often have higher values, such as 2.5 to 4, because obstacles and reflections cause additional signal loss.
