How far does Bluetooth Low Energy reach?

The Bluetooth SIG answers the question with a span rather than a number: “more than a kilometer. Less than a meter.” Its range page explains that Bluetooth is designed to support a wide range of distances, so that product designers can choose what suits their use case. A wearable that should only talk to the phone in your pocket and an industrial sensor across a yard are both valid Bluetooth Low Energy designs.

So the useful question is not “how far does BLE reach?” but “how far will these two devices reach here?” That depends on a short list of factors.

The SIG lists the main ones:

• Radio spectrum. Lower frequencies travel farther but carry less data. Bluetooth uses the 2.4 GHz ISM band (2400 to 2483.5 MHz), which the SIG describes as a balance between range and throughput that is available worldwide.
• PHY. The physical layer sets the modulation and whether error correction is used. LE 1M and LE 2M are uncoded; the LE Coded PHY adds forward error correction so the receiver can decode a weaker signal, at a lower data rate.
• Receiver sensitivity. This is the weakest signal a receiver can still demodulate. The specification requires a minimum of -70 dBm to -82 dBm depending on the PHY, and the SIG notes that real implementations usually do much better, with average LE Coded implementations reaching -103 dBm.
• Transmit power. Bluetooth supports transmit powers from -20 dBm (0.01 mW) to +20 dBm (100 mW). More power means a longer reach and more energy used. Regulators in each market can set a lower ceiling, which the SIG’s technology overview notes devices must not exceed.
• Antenna gain. Antenna design, placement and package size change how well a device sends and receives. The SIG says Bluetooth devices typically achieve antenna gain from -10 dBi to +10 dBi.
• Path loss. Signal strength falls with distance and with what is in the way. The SIG lists humidity and rain, walls, windows, and obstacles of glass, wood, metal or concrete, as well as metal structures that reflect and scatter radio waves.

These factors add up along the link. A strong transmitter cannot make up for a deaf receiver behind a concrete wall, and a sensitive receiver gains little if the other device whispers through a poor antenna.

A module’s data sheet describes the module, not the product it ends up in, and a phone is a harder case than most. Its antenna has to share a small case with other radios, and the SIG notes that antenna location, package size and design can greatly affect performance. The phone may also be in a pocket, a bag or a vehicle.

Apps also control only part of the radio budget. On Android, an app can request an advertising transmit power level: AdvertiseSettings.ADVERTISE_TX_POWER_HIGH is documented as the level with the largest visibility range of the advertising packet, and extended advertising sets accept a transmit power from -127 to 20 dBm through AdvertisingSetParameters.Builder.setTxPowerLevel.

Range is also not symmetric. Each direction of a link has its own transmitter, antenna and receiver, so device A may hear device B at a distance where B can no longer hear A. A connection needs both directions to work.

Published distances vary widely. In a 2017 post on the SIG’s blog, Martin Woolley reported an informal test in which a basic Android phone received notifications from a BLE microcontroller at over 350 metres, in a setting with many people and trees in the way, using Bluetooth Core 4.0. The author described the environment as sub-optimal for radio, so the result shows that LE 1M can reach a long way, but it is one informal measurement, not a typical figure.

Treat any single distance figure as a data point, and ask what PHY, transmit power, antennas and environment produced it.

To find the range that matters for your product:

1. Test the exact devices you will ship, in the place they will be used, at several distances and orientations.
2. Test both directions, and test with a connection carrying real traffic, not only with advertisements.
3. Note the received signal strength (RSSI) and the error or retry rate as you move apart, not only the point where the link drops.

If the range is not enough, there are three main levers: use a PHY with more coding, raise transmit power within legal limits and the battery budget, or add hops. The SIG’s range page also links an online range estimator for planning. In a mesh, multi-hop relay lets messages reach devices far beyond one radio link, as long as enough participating devices sit in between. Each of these choices has costs in battery and in throughput.