Wi-Fi Signal (dBm) & SNR Quality Calculator

Understanding the Wi-Fi signal strength calculator — concept and principle

Wi-Fi tools report received signal strength (RSSI) in dBm, a logarithmic scale where values are negative and closer to zero is stronger. This calculator turns a signal reading and the noise floor into a signal-to-noise ratio (SNR), gives a plain-language quality rating, and converts the dBm value into actual power in nanowatts. Use it when surveying a home or office, choosing where to place access points, or checking whether a spot is good enough for video calls.

SNR is simply the gap between signal and noise in dB; 33 dB clears the common 25 dB target.

How it is calculated

SNR (dB) = signal (dBm) − noise floor (dBm).
Power (mW) = 10^(dBm ÷ 10); the calculator multiplies by 10^6 to show nanowatts.
Quality bands used here: −50 dBm or better excellent; −60 very good; −67 good (voice/video OK); −70 fair; −80 weak; below −80 unusable.

The principle

dBm means decibels relative to 1 milliwatt: 0 dBm = 1 mW, −30 dBm = 1 µW, −60 dBm = 1 nW. Each 10 dB is a factor of 10 in power and each 3 dB about a factor of 2. Because both signal and noise are in dBm, subtracting them gives their ratio in dB. A higher SNR lets the radio use denser modulation and faster data rates; as SNR drops, the link falls back to slower rates and retransmits more. Radio power also spreads out with distance and is absorbed by walls, so readings fall quickly as you move away from the access point.

Worked example

Inputs: signal −62 dBm, noise floor −95 dBm.
SNR: −62 − (−95) = 33 dB.
Quality: −62 is below −60 but at or above −67, so good (voice/video OK).
Power: 10^(−62 ÷ 10) = 10^−6.2 = 6.31 × 10^−7 mW.
In nanowatts: 6.31 × 10^−7 × 10^6 = 0.631 nW.

Each point is the calculator re-run with only “Noise floor (dBm)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Noise floor (dBm)	SNR (dB)
-23.8	-38.25
-47.5	-14.5
-71.2	9.25
-95	33
-119	56.75
-142	80.5
-190	128

How to read the result

A widely used target for voice and video is a signal of −67 dBm or better with an SNR of at least 25 dB. An SNR of 33 dB, as in the example, is comfortable. Below about −70 dBm, throughput drops and calls may break up; below −80 dBm the link is unreliable. Readings fluctuate by several dB, so take a few samples.

Common mistakes

Thinking −70 is stronger than −60; in dBm, the number closer to zero is stronger.
Treating the 0–100% "signal bars" of an operating system as dBm; they use vendor-specific scales.
Ignoring the noise floor; a strong signal in a noisy band can still perform badly.

Keep in mind: Quality bands are common guidance, not standards. Interference, channel width, client device and number of users all affect real performance.

Frequently asked questions

Is −62 dBm a good Wi-Fi signal?

Yes. It is better than the −67 dBm often recommended for voice and video.

What is a typical noise floor?

In quiet conditions roughly −90 to −95 dBm; busy environments can be higher.

How much does a 3 dB drop mean?

About half the received power.

Sources: IEEE Std 802.11, Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications · IEC 60027-3, Letter symbols to be used in electrical technology, Part 3: Logarithmic and related quantities, and their units

Checked 8 Nov 2026. Standard formulas and RFC/IEEE definitions, computed locally in your browser — nothing you type is sent anywhere.

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