Convert between decibels (dB), decibel-milliwatts (dBm), and milliwatts (mW) instantly. This tool helps network engineers, WiFi professionals, and radio enthusiasts understand signal power levels — all calculations run locally in your browser.
Decibels (dB) and decibel-milliwatts (dBm) are logarithmic units used to express power levels in networking, radio, and telecommunications. Understanding these units is essential for anyone working with WiFi signals, antenna systems, or signal strength measurements.
The formula for conversion is: P(mW) = 10^(P(dBm)/10) and inversely: P(dBm) = 10 * log10(P(mW)).
WiFi signal strength is measured in dBm and is always a negative number (because WiFi power levels are fractions of a milliwatt at the receiver). Here are the ranges you need to know when checking your connection quality with the Speed Test tool:
| dBm Range | Signal Quality | Expected Performance | mW Equivalent |
|---|---|---|---|
| -30 to -20 dBm | Excellent | Maximum speed, very close to AP | 0.001 – 0.01 mW |
| -50 to -30 dBm | Excellent | Full speed reliable connection | 0.00001 – 0.001 mW |
| -60 to -50 dBm | Very Good | Streaming, video calls, gaming | 0.000001 – 0.00001 mW |
| -70 to -60 dBm | Good | Web browsing, email reliable | 0.0000001 – 0.000001 mW |
| -80 to -70 dBm | Fair | Basic connectivity, possible drops | 0.00000001 – 0.0000001 mW |
| -90 to -80 dBm | Weak | Frequent disconnects, very slow | 0.000000001 – 0.00000001 mW |
| Below -90 dBm | Unusable | Connection unlikely | < 0.000000001 mW |
Pro Tip: A difference of just 3 dBm represents a doubling or halving of actual power. Going from -70 dBm to -67 dBm doubles your received signal power. When troubleshooting WiFi issues, even small dBm improvements can significantly impact performance. Use our Signal Strength Converter to translate between dBm and percentage.
Because decibels are logarithmic, simple rules make mental math easy. These rules apply universally whether you are calculating antenna gain, cable loss, or amplifier output:
| dB Change | Power Multiplier | Practical Meaning |
|---|---|---|
| +3 dB | 2x (double) | Double the power |
| +6 dB | 4x | Quadruple the power |
| +10 dB | 10x | Ten times the power |
| +20 dB | 100x | Hundred times the power |
| +30 dB | 1000x | Thousand times the power |
| -3 dB | 0.5x (half) | Half the power |
| -10 dB | 0.1x | One-tenth the power |
| -20 dB | 0.01x | One-hundredth the power |
Understanding typical transmit power helps you interpret signal readings. Most consumer routers transmit at 15-20 dBm on the 2.4 GHz band and 15-23 dBm on the 5 GHz band. Here's a reference for common equipment:
| Device / Class | Typical Tx Power (dBm) | Power (mW) | Notes |
|---|---|---|---|
| Smartphone WiFi | 12-15 dBm | 16-32 mW | Limited by battery and SAR regulations |
| Laptop WiFi | 15-18 dBm | 32-63 mW | Varies by adapter |
| Consumer router (2.4 GHz) | 17-20 dBm | 50-100 mW | FCC limit: 30 dBm EIRP |
| Consumer router (5 GHz) | 15-23 dBm | 32-200 mW | Channel-dependent limits |
| Enterprise AP | 20-24 dBm | 100-250 mW | Adjustable per radio |
| Outdoor point-to-point | 24-30 dBm | 250-1000 mW | With directional antenna |
A link budget calculates whether a wireless link will work by adding gains and subtracting losses along the signal path. The formula is:
Received Power (dBm) = Tx Power (dBm) + Tx Antenna Gain (dBi)
- Cable Loss (dB) - Free Space Path Loss (dB)
+ Rx Antenna Gain (dBi) - Rx Cable Loss (dB)If the received power exceeds the receiver sensitivity (typically -80 to -90 dBm for WiFi), the link will work. This is why improving antenna gain by just 3 dBi can make a marginal link reliable. For testing your actual connection performance, combine this knowledge with our Ping Test and Network Latency Test.
While this tool focuses on WiFi applications, dBm is also the standard power measurement in fiber optics. The key difference is the power levels involved:
For wired network considerations, see our guide on Cat5e vs Cat6 Ethernet and the Cable Length Calculator for maximum run distances.
You can measure your current WiFi signal strength using built-in OS tools:
netsh wlan show interfaces | findstr "Signal"Note: Windows reports signal as a percentage. Use our Signal Strength Converter to convert to dBm.
# Hold Option key and click WiFi icon in menu bar
# Or use: /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -Iiwconfig wlan0 | grep "Signal level"
# or
iw dev wlan0 linkFor a quick browser-based check, run our Speed Test to see if your throughput matches what your signal strength should deliver. Compare results using the Bandwidth Calculator.
dB (decibel) is a relative unit that expresses the ratio between two power levels — it tells you how much stronger or weaker one signal is compared to another. dBm (decibel-milliwatt) is an absolute unit that measures power referenced to 1 milliwatt. Think of dB as a comparison and dBm as an actual measurement.
For most applications, -50 to -65 dBm is considered very good and supports streaming, video calls, and gaming without issues. For basic web browsing and email, -65 to -75 dBm is acceptable. Below -80 dBm, you'll experience frequent disconnections and very slow speeds.
WiFi signal strength at the receiver is always negative dBm because the received power is less than 1 milliwatt (0 dBm). Even a strong WiFi signal like -30 dBm equals only 0.001 mW — far below the 1 mW reference point. The transmitter outputs positive dBm, but signal loss over distance makes the received value negative.
A 3 dBm change represents a doubling or halving of actual power. Going from -73 dBm to -70 dBm doubles your received signal power, which can make the difference between a flaky connection and a stable one. This is why antenna positioning and obstacle removal are so impactful.
Increasing transmit power helps to a point but has diminishing returns. Most consumer routers already transmit at or near regulatory limits. Better strategies include repositioning your router, reducing obstacles, using a higher-gain antenna, or switching to a less congested channel. Check our WiFi speed testing guide for optimization steps.
For a typical 2,000 sq ft home, you need about -65 dBm or better at the farthest point for reliable connectivity. A router transmitting at 20 dBm with standard antennas can typically cover this if placed centrally. Walls, floors, and appliances each reduce signal by 3-15 dB depending on material. Use our Signal Strength Converter to interpret readings from your device.
RSSI (Received Signal Strength Indicator) is a vendor-specific measurement that some WiFi adapters report instead of dBm. RSSI values vary by manufacturer — some use 0-100, others 0-255. There is no universal RSSI-to-dBm formula, but many adapters use approximately: dBm = RSSI - 95. Always prefer dBm readings when available as they are standardized.
About Tommy N.
Tommy is the founder of RouterHax and a network engineer with 10+ years of experience in home and enterprise networking. He specializes in router configuration, WiFi optimization, and network security. When not writing guides, he's testing the latest mesh WiFi systems and helping readers troubleshoot their home networks.
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