Tx power, short for transmit power, is the strength of the radio signal a wireless device sends out. It’s measured in dBm (decibel-milliwatts), and it directly determines how far your Wi-Fi router, Bluetooth device, or IoT sensor can reach. A typical home router transmits at around 20 to 30 dBm, while a Bluetooth device might use just 8 dBm. The higher the number, the stronger and farther the signal travels.
How Tx Power Is Measured
Tx power uses a unit called dBm, which stands for decibels relative to one milliwatt. A reading of 0 dBm equals exactly 1 milliwatt of power. The scale is logarithmic, which means small number changes represent big real-world differences. Every increase of 3 dBm roughly doubles the actual power output, and every increase of 10 dBm multiplies it by ten. So 10 dBm (10 milliwatts) is ten times more powerful than 0 dBm (1 milliwatt), and 20 dBm (100 milliwatts) is a hundred times more powerful than 0 dBm.
You’ll sometimes see tx power listed in milliwatts instead of dBm, especially on product spec sheets. Both describe the same thing. A router listed at 1 watt (1,000 milliwatts) is transmitting at 30 dBm.
How Tx Power Affects Range
Radio waves lose strength as they travel because power density drops with the square of the distance. Every time you double the distance from the transmitter, you receive only one-fourth the signal power. Working backward from the dBm scale, every 6 dBm increase in tx power approximately doubles the achievable range.
This is why cranking up the power doesn’t produce as dramatic a range boost as you might expect. Going from 20 dBm to 26 dBm doubles your range, but you’d need to jump all the way to 32 dBm to double it again. Higher tx power also helps signals punch through walls, floors, and other obstacles, which is why access points in large buildings often run at higher power levels than a small apartment router needs.
A practical example: a LoRaWAN sensor set to +20 dBm can reach a gateway several kilometers away in open conditions, while the same device at +14 dBm might only cover half that distance.
Typical Power Levels by Device
Different types of wireless hardware operate at very different tx power levels:
- Bluetooth Low Energy (BLE) devices: Default tx power is typically +8 dBm. European regulations cap Bluetooth connections at +20 dBm when adaptive frequency hopping is active, and +10 dBm when it’s not. Bluetooth advertisements are generally limited to +10 dBm.
- Wi-Fi routers and access points: Most home routers transmit between 20 and 30 dBm (100 milliwatts to 1 watt). Enterprise access points can push up to 30 dBm on both 2.4 GHz and 5 GHz bands.
- Smartphones and client devices: Phones and laptops typically transmit at lower levels than routers. On the 5 GHz low band, for example, FCC rules cap client devices at 250 milliwatts (24 dBm).
- IoT sensors: These range widely depending on the protocol, from as low as 0 dBm for short-range sensors to +20 dBm or more for long-range outdoor deployments.
Regulatory Limits
Governments set maximum tx power levels to prevent devices from interfering with each other. In the United States, the FCC enforces these limits by frequency band. On the 2.4 GHz band commonly used for Wi-Fi, the maximum power from the radio itself is 1 watt (30 dBm), with total radiated power (including antenna gain) capped at 4 watts (36 dBm) for point-to-multipoint setups.
The 5 GHz bands have stricter, more varied rules. The lower 5 GHz band (5.15 to 5.25 GHz) allows up to 1 watt for access points, both indoors and outdoors. The mid and extended 5 GHz bands (5.25 to 5.725 GHz) are capped at 200 milliwatts (23 dBm). Other countries have their own regulatory bodies and limits. Europe’s ETSI rules, for instance, tend to be more conservative than FCC limits, particularly on the 2.4 GHz band.
Why Higher Isn’t Always Better
It’s tempting to set tx power to the maximum, but that often creates more problems than it solves. Higher tx power drains batteries faster in phones, sensors, and laptops. For battery-powered IoT devices deployed in the field, the difference between +14 dBm and +20 dBm can meaningfully shorten battery life over months of operation.
There’s also a network performance issue. If your router blasts a powerful signal but your phone responds at a much lower power level, you end up with an asymmetric link. Your phone can hear the router fine, but the router struggles to hear your phone. The result is a connection that looks strong on your phone’s signal indicator but performs poorly in practice.
In dense environments like apartment buildings or offices, high tx power causes interference with neighboring networks. Every device on the same channel competes for airtime, and a louder signal doesn’t help if it’s drowning out everyone else in the process. Modern wireless systems use transmit power control (TPC) to automatically dial power up or down based on conditions, balancing range against interference and energy use.
Adjusting Tx Power on Your Devices
Most consumer routers let you adjust tx power through their admin settings, usually as a percentage of maximum or as a low/medium/high option. Some advanced routers and access points let you set a specific dBm value. If you’re in a small apartment and your signal bleeds into neighboring units, reducing tx power can actually improve your network performance by reducing interference and encouraging your devices to connect to the nearest access point.
For home networks covering a single room or small apartment, 15 to 20 dBm is often sufficient. Larger homes or spaces with thick walls may benefit from keeping power at 20 to 23 dBm. If you need to cover a very large area, adding a second access point at moderate power is almost always more effective than running one access point at maximum power. The goal is to match your tx power to the actual coverage area you need, not to maximize it by default.