Choose estimated distance, model RSSI or model reference power at 1 m, then enter the known values. Distances support meters, cm, km, feet, yards and miles.

Uses the log-distance model with fixed n = 2 and a 1 m reference. Enter calibrated received power at 1 m, not the transmitter’s output setting.

Use the signed RSSI reading. A value of 0 dBm is valid arithmetic.

Often called measured power or beacon Tx power. Use the value calibrated for your beacon and receiver.

Related 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 = calibrated received power at 1 meter, in dBm (not transmitter output power)
  • n = path loss exponent, fixed at 2 in this calculator
  • log10 = base-10 logarithm

Select the value to solve for, then enter the two displayed inputs. Here Tx means calibrated received power at 1 m. Distance values are converted to meters for the formula, then converted back to your selected unit when distance is the result.

Illustrative Beacon Signal Levels

RSSI values are usually negative. A value closer to 0 means a stronger received signal.

RSSI range Relative signal level Distance-model limitation
-30 to -50 dBm Higher received power No universal accuracy follows from this range
-51 to -70 dBm Lower received power Requires calibration and environmental checks
-71 to -90 dBm Still lower received power RSSI alone does not establish distance accuracy
Below -90 dBm Lowest listed received power Usable range depends on the receiver and environment

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 = 1609.344 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 conditions vary; obstacles and reflections can invalidate the fixed n = 2 assumption.