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BLE Link Budget & Range Calculator — Bluetooth Low Energy by PHY

Bluetooth Low Energy link budget by PHY: data rate and Core Specification receiver sensitivity for LE 1M, LE 2M and LE Coded, path loss in free space or the ITU-R P.1238 indoor model, received power, link margin and maximum range.

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Formula

M=PTX+GTX+GRX−L−Lp−S,LpFS=20log⁡104πdfc,LpP.1238=10αlog⁡10d+β+10γlog⁡10fGHzM = P_{TX} + G_{TX} + G_{RX} - L - L_p - S,\quad L_p^{FS} = 20\log_{10}\frac{4\pi d f}{c},\quad L_p^{P.1238} = 10\alpha\log_{10} d + \beta + 10\gamma\log_{10} f_{GHz}

Reference: Bluetooth Core Specification v5.4, Vol 6, Part A, §1–§4; ITU-R P.1238-13, §3.1, Table 2; ITU-R P.525-4, Eq. (3)

S— Receiver sensitivity: −70 dBm (1M, 2M), −75 dBm (Coded S=2), −82 dBm (Coded S=8), or the datasheet value (dBm)
L_p— Path loss (dB)
\alpha, \beta, \gamma— ITU-R P.1238 distance, offset and frequency coefficients for the environment
d— Direct distance (m)
f— Frequency (Hz (free space), GHz (P.1238))

How It Works

Bluetooth Low Energy links are short, so their budget turns mostly on the receiver: which physical layer (PHY) carries the data, and how sensitive the radio is.

The four LE PHYs

The Bluetooth Core Specification defines LE 1M, the mandatory PHY, at 1 Mb/s; LE 2M at 2 Mb/s; and the coded PHY, which repeats each bit to trade rate for range: 500 kb/s with S=2 coding and 125 kb/s with S=8. A compliant receiver must reach the sensitivity of Table 4.2 in Volume 6, Part A: −70 dBm for the uncoded PHYs, −75 dBm for S=2 and −82 dBm for S=8. These are the worst a qualified radio may have, and most current radios do 20 to 30 dB better, so enter the datasheet value where you know it.

Path loss

In free space the loss is 20log⁡10(4πdf/c)20\log_{10}(4\pi d f/c): 60.20 dB at 2440 MHz and 10 m (ITU-R P.525). Indoors, ITU-R P.1238 gives a site-general model fitted to measurements,

L=10αlog⁡10d+β+10γlog⁡10fL = 10\alpha\log_{10} d + \beta + 10\gamma\log_{10} f

with dd the direct distance in metres and ff the frequency in GHz, and coefficients for offices, corridors, industrial halls and conference rooms, in line of sight (LoS) and out of it (NLoS). Through an office out of sight α\alpha = 2.39, β\beta = 30.13 and γ\gamma = 2.40, so the loss at 10 m and 2.44 GHz is 63.33 dB, and it grows by 23.9 dB for every tenfold increase in distance instead of the 20 dB of free space. Each environment also has a shadow-fading standard deviation, 5.01 dB for that office, which is shown to help choose a fade margin.

Margin and range

The received power is the transmit power plus both antenna gains, less the other losses and the path loss. The link margin is that power less the sensitivity, and the maximum range is the distance at which the margin reaches zero.

Validity

The Core Specification allows transmit powers from −20 to +20 dBm at the maximum power setting, and LE operates from 2400 to 2483.5 MHz; values outside those ranges are shown with a warning. Each P.1238 environment holds over the frequencies and distances it was measured at, such as 4 to 30 m for an office out of sight; a distance or a maximum range outside that range is flagged. The path loss is a median with no fade margin, and body and enclosure losses count only if you enter them.

Worked Example

Problem: A sensor on the LE 1M PHY transmits 0 dBm through a 0 dBi chip antenna to a gateway 10 m away across an office, out of sight. Does the link close, and how far could it reach? Then compare the LE Coded S=8 PHY, and a radio whose datasheet gives −97 dBm on LE 1M.

Step 1 - Path loss (ITU-R P.1238, office NLoS): L = 23.9 log₁₀(10) + 30.13 + 24.0 log₁₀(2.44) = 23.9 + 30.13 + 9.30 = 63.33 dB

Step 2 - Received power: P_RX = 0 + 0 + 0 − 0 − 63.33 = −63.33 dBm

Step 3 - Margin with the Core Specification sensitivity: M = −63.33 − (−70) = 6.67 dB Maximum range: 19.02 m

Step 4 - LE Coded S=8 (−82 dBm): M = 18.67 dB, maximum range 60.43 m, beyond the 30 m the office NLoS coefficients cover, so it is flagged

Step 5 - A −97 dBm datasheet sensitivity on LE 1M: M = 33.67 dB

In free space the same 10 m would cost 60.20 dB. Indoors the extra 3.13 dB and the steeper slope cut the range at −70 dBm from 30.92 m to 19.02 m.

Practical Tips

  • ✓Enter your radio's datasheet sensitivity for the PHY you use; leave the field at 0 to see the Core Specification minimum.
  • ✓Pick the ITU-R P.1238 environment that matches the room, and keep the distance inside its range: 4 to 30 m for an office out of sight.
  • ✓Keep at least one shadow-fading standard deviation of link margin, more for a link that must not drop.
  • ✓Use the LE Coded PHY only where the range is needed: at S=8 the throughput falls to 125 kb/s.

Common Mistakes

  • ✗Budgeting with the Core Specification sensitivity and concluding that BLE reaches only a few metres. The −70 dBm requirement is a floor for compliance; a datasheet value is usually 20 dB or more better.
  • ✗Using free-space loss indoors. Walls and furniture make the loss grow faster with distance, so a free-space range can be more than half again too long.
  • ✗Expecting the coded PHY to cost nothing. S=8 gains 12 dB of sensitivity by sending each bit eight times, so a packet takes about eight times as long and uses more energy.
  • ✗Leaving out body and enclosure losses. A wearable or a device in a metal box can lose several decibels that never appear in a datasheet.

Frequently Asked Questions

It depends on the PHY, the radio and the building. With 0 dBm, no antenna gain and the Core Specification minimum of −70 dBm, an office out of sight limits LE 1M to about 19 m; a radio with −97 dBm sensitivity, or the coded PHY, reaches much farther.
The Core Specification requires at least −70 dBm on the LE 1M and LE 2M PHYs, −75 dBm on the coded PHY with S=2 coding and −82 dBm with S=8 coding. Real radios are usually much better than these minimums.
It is the long-range PHY introduced in Bluetooth 5. It codes each bit at 1 Msym/s with forward error correction, giving 500 kb/s with S=2 or 125 kb/s with S=8, in exchange for 5 or 12 dB of extra sensitivity over LE 1M.
The Core Specification allows a maximum power setting between −20 dBm and +20 dBm, in power classes 1 to 3. Regional regulations may set a lower limit.
It uses the site-general model of Recommendation ITU-R P.1238, with the coefficients for offices, corridors, industrial halls and conference rooms in line of sight or out of it, valid over the frequencies and distances each was measured at.

Methodology & References

References

  • Bluetooth Core Specification, Version 5.4 — Bluetooth SIG, 2023 — Vol 6, Part A: §1 (LE PHYs and rates), §2 (2400–2483.5 MHz), §3 and Table 3.1 (transmit power), §4.1 and Table 4.2 (receiver sensitivity) link
  • Recommendation ITU-R P.1238-13, Propagation data and prediction methods for the planning of indoor radiocommunication systems — ITU-R, 09/2025 — §3.1, Eq. (1) and Table 2, site-general basic transmission loss coefficients link
  • Recommendation ITU-R P.525-4, Calculation of free-space attenuation — ITU-R, 08/2019 — §2.2, Eq. (3) link

Uses the Core Specification sensitivities (−70, −70, −75 and −82 dBm) and rates (1, 2, 0.5 and 0.125 Mb/s) for the four LE PHYs, reproduces the 60.20 dB free-space loss at 2440 MHz and 10 m, and the ITU-R P.1238-13 office NLoS coefficients exactly.

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