Wifi rssi signal strength

How to convert Wifi signal strength from Quality (percent) to RSSI (dBm)?

How should I convert Wifi signal strength from a Quality in percentage, usually 0% to 100% into an RSSI value, usually a negative dBm number (i.e. -96db )?

12 Answers 12

Wifi Signal Strength Percentage to RSSI dBm

Microsoft defines Wifi signal quality in their WLAN_ASSOCIATION_ATTRIBUTES structure as follows:

wlanSignalQuality:

A percentage value that represents the signal quality of the network. WLAN_SIGNAL_QUALITY is of type ULONG. This member contains a value between 0 and 100. A value of 0 implies an actual RSSI signal strength of -100 dbm. A value of 100 implies an actual RSSI signal strength of -50 dbm. You can calculate the RSSI signal strength value for wlanSignalQuality values between 1 and 99 using linear interpolation.

RSSI (or «Radio (Received) Signal Strength Indicator«) are in units of ‘dB’ (decibel) or the similar ‘dBm’ (dB per milliwatt) (See dB vs. dBm) in which the smaller magnitude negative numbers have the highest signal strength, or quality.

Therefore, the conversion between quality (percentage) and dBm is as follows:

 quality = 2 * (dBm + 100) where dBm: [-100 to -50] dBm = (quality / 2) - 100 where quality: [0 to 100] 

Pseudo Code (with example clamping):

 // dBm to Quality: if(dBm = -50) quality = 100; else quality = 2 * (dBm + 100); // Quality to dBm: if(quality = 100) dBm = -50; else dBm = (quality / 2) - 100; 

Check the definition of Quality that you are using for your calculations carefully. Also check the range of dB (or dBm ). The limits may vary.

Medium quality: 50% -> -75dBm = (50 / 2) - 100 Low quality: -96dBm -> 8% = 2 * (-96 + 100) 

In JS I prefer doing something like:

Math.min(Math.max(2 * (x + 100), 0), 100)

My personal opinion is that it’s more elegant way to write it, instead of using if ‘s.

1. Less than -50dB (-40, -30 and -20) = 100% of signal strength
2. From -51 to -55dB= 90%
3. From -56 to -62dB=80%
4. From -63 to -65dB=75%

Im glad I found this post cause I was looking for a way to convert the dbm to percentage. Using David’s post, I wrote up a quick script in python to calculate the quality percentage.

#!/usr/bin/env python3 import os import platform system = platform.system() if system == 'Linux': cmd = "iwconfig wlan0 | grep Signal | /usr/bin/awk '' | /usr/bin/cut -d'=' -f2" elif system == 'Darwin': cmd = "/System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -I | grep CtlRSSI | awk '< print $NF; >" else: print("Unsupported os: <>".format(system)) dbm = os.popen(cmd).read() if dbm: dbm_num = int(dbm) quality = 2 * (dbm_num + 100) print(" dbm_num = %".format(dbm_num, quality)) else: print("Wifi router connection signal strength not found") 

In order to get the highest wifi quality from where my computer is located, I moved/rotated my antenna until I received the highest quality. To see real time quality, I ran the above script using:

watch -n0.1 "python getwifiquality.py" 

I know this may be late but this may help someone in the future.

I took the value of dBm 30-90 for RSSI and correlated it to 100-0 %.

I used the basic linear equation to get the answer.

We know our x values for dBm as 30 and 90. We know our y values for % as 100 and 0.

We just need to find the slope. So we can make it linear.

m = 100-0/30-90 = 100/-60 = -5/3 b = y - mx = 0 + 5/3*90 = 150 

Final equation to put in code when you know the RSSI value.

Note I did take the RSSI value that is normally negative and multiplied by the absolute value to get positive numbers.

quality = abs(RSSI) % = 150 - (5/3) * quality 

RSSI — Received Signal Strength Indicator RSS — Received Signal Strength

RSSI is an indicator and RSS is the real value. Ok, now what do you mean by indicator, indicator mean it can be a relative value and RSSI is always a positive value and there is no unit for the RSSI.

We can say RSSI is for common man to understand. RF values are always told in dBm and the values are negative values most of the time. To make it easy for the people to understand these negative values are converted to positive values through scaling.

Say for example, if the maximum signal strength is 0 dBm and minimum is -100 dBm . We can scale it like as explained. We can put 0 dBm and more (RSS) as 100 RSSI (i. e. maximum RSSI) and -100 dBm (or less) as 0 RSSI (minimum RSS).

long rssi = WiFi.RSSI(); rssi=-rssi; int WiFiperct; if (rssi <27)< WiFiperct =100; >else if(rssi>=27&&rssi <33)< WiFiperct=150-(5/2.7)*rssi; >else if(rssi>=33&&rssi <36)< WiFiperct=150-(5/3)*rssi; >else if(rssi>=36&&rssi <40)< WiFiperct=150-(5/3.3)*rssi; >else if(rssi>=40&&rssi <80)< WiFiperct=150-(5/3.5)*rssi; >else if(rssi>=80&&rssi <90)< WiFiperct=150-(5/3.4)*rssi; >else if(rssi>=90&&rssi <99)< WiFiperct=150-(5/3.3)*rssi; >else

This article is a more detailed explanation of mW, dBm and RSSI

According to it RSSI do not have a unit. It’s a value defined in 802.11 standard and calculated by nic card and sent to OS. The nic card vendor should provide a mapping table of dBm-RSSI values.

Sorry for the direct link, but I can not found the original page for the file link.

Mentioned pseudocode will not work all the ranges, the ranges example (-80dBm to 0, and -40dBm to 100).

Generic simple logic to map any range to 0 to 100. Usage example, for below code ConvertRangeToPercentage(-80,-40,-50)

int ConvertRangeToPercentage (int a_value_map_to_zero, int a_value_map_to_100, int a_value_to_convert) < int percentage = 0; if (a_value_map_to_zero < a_value_map_to_100) < if (a_value_to_convert else if (a_value_to_convert >= a_value_map_to_100) < percentage = 100; >else < percentage = (a_value_to_convert - a_value_map_to_zero) * 100 / (a_value_map_to_100 - a_value_map_to_zero); >> else if (a_value_map_to_zero > a_value_map_to_100) < if (a_value_to_convert >= a_value_map_to_zero) < percentage = 0; >else if (a_value_to_convert else < percentage = (a_value_to_convert - a_value_map_to_zero) * 100 / (a_value_map_to_100 - a_value_map_to_zero); >> else < percentage = 0; >return percentage; > 

Ok.. I agree. but why is then:

 Quality=29/100 Signal level=-78 dBm Quality=89/100 Signal level=-55 dBm Quality=100/100 Signal level=-21 dBm 

this does not agree with the formula percentage=quality/2 — 100.

There is no universally-agreed meaning of ‘quality’. Microsoft has one definition, described in the accepted answer, but other software may not use this definition. For example, WiFi Explorer says that -20 dBm is 100%, and even points out that «other tools show percentage values for signal strength that are far off from what you see in WiFi Explorer.»

Also, you can try inverse this Bash function which converts dBm to percentage:

#!/bin/bash function dbmtoperc < # Convert dBm to percentage (based on https://www.adriangranados.com/blog/dbm-to-percent-conversion) dbmtoperc_d=$(echo "$1" | tr -d -) dbmtoperc_r=0 if [[ "$dbmtoperc_d" =~ 7+$ ]]; then if ((1

echo $(dbmtoperc -48)% # returns 81% 

Article you point is erroneous because dBm is already a nonlinear logarithmic represent of mW. So this solution is logarithm of logarithm. So we have "signal quality is double logarithm of signal power" - this is nonsense.

@imbearr You might be right, but this values were figured by real situation. What's your solution then?

I'm prefer to use solution proposed by David Manpearl. This is simple linear convertation, it produce only even values of percent but I think we can't doing something better, because we have only integer dbm value as source.

Airodump RXQ is really usefull in the real world conditions. "Receive Quality as measured by the percentage of packets (management and data frames) successfully received over the last 10 seconds." "Its measured over all management and data frames. The received frames contain a sequence number which is added by the sending access point. RXQ = 100 means that all packets were received from the access point in numerical sequence and none were missing. That's the clue, this allows you to read more things out of this value. Lets say you got 100 percent RXQ and all 10 (or whatever the rate) beacons per second coming in. Now all of a sudden the RXQ drops below 90, but you still capture all sent beacons. Thus you know that the AP is sending frames to a client but you can't hear the client nor the AP sending to the client (need to get closer)."

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Understanding RSSI

RSSI, or “Received Signal Strength Indicator,” is a measurement of how well your device can hear a signal from an access point or router. It’s a value that is useful for determining if you have enough signal to get a good wireless connection.

Note: Because an RSSI value is pulled from the client device’s WiFi card (hence “received” signal strength), it is not the same as transmit power from a router or AP.

Basic WiFi Lessons

Need Help Measuring WiFi Signal Strength?

Track signal strength in your environment and see how it changes over time with MetaGeek Plus!

RSSI vs dBm

dBm and RSSI are different units of measurement that both represent the same thing: signal strength. The difference is that RSSI is a relative index, while dBm is an absolute number representing power levels in mW (milliwatts).

RSSI is a term used to measure the relative quality of a received signal to a client device, but has no absolute value. The IEEE 802.11 standard (a big book of documentation for manufacturing WiFi equipment) specifies that RSSI can be on a scale of 0 to up to 255 and that each chipset manufacturer can define their own “RSSI_Max” value. Cisco, for example, uses a 0-100 scale, while Atheros uses 0-60. It’s all up to the manufacturer (which is why RSSI is a relative index), but you can infer that the higher the RSSI value is, the better the signal is.

Since RSSI varies greatly between chipset manufacturers, MetaGeek software uses a more standardized, absolute measure of signal strength: received signal power, which is measured in decibels, or dBm on a logarithmic scale. There’s a lot of math we could get into, but basically, the closer to 0 dBm, the better the signal is.

To help leverage your signal strength measurement most effectively so you can make channel planning decisions, inSSIDer displays signal strength in two ways.

The Networks Table visualizes where selected networks are located on the 2.4 or 5 GHz band in relation to other networks, and the signal strengths of each.

The Signal Strength Over Time graph shows how your network’s signal strengths changes as you move around the room or office.

Acceptable Signal Strengths

Signal Strength	TL;DR	Required for
-30 dBm	Amazing	Max achievable signal strength. The client can only be a few feet from the AP to achieve this. Not typical or desirable in the real world.	N/A
-67 dBm	Very Good	Minimum signal strength for applications that require very reliable, timely delivery of data packets.	VoIP/VoWiFi, streaming video
-70 dBm	Okay	Minimum signal strength for reliable packet delivery.	Email, web
-80 dBm	Not Good	Minimum signal strength for basic connectivity. Packet delivery may be unreliable.	N/A
-90 dBm	Unusable	Approaching or drowning in the noise floor. Any functionality is highly unlikely.	N/A

What if I have an acceptable signal strength but I’m still having problems?

If you’ve already checked your signal strength using a WiFi scanning app like inSSIDer and concluded that you have acceptable WiFi signal strength, then interference may be to blame. Your computer’s WiFi adapter can help you see some types of interference, but for finding non-WiFi interferers, you’ll need a spectrum analysis tool like Wi-Spy.

To view this video please enable JavaScript, and consider upgrading to a web browser that supports HTML5 video

The signal strength of the “MetaGeek” SSID is great (approx. -50dBm), but the actual wireless signal is being destroyed by a non-WiFi interferer, which is shown above with a large green spiky shape between channels 5 and 6.

Looking for Mobile WiFi Tools?

Wi-Spy Air is the fast, portable and accurate way to validate and troubleshoot WiFi environments. Level up your iOS or Android device with Wi-Spy Air’s onboard WiFi chipset, transforming it into a professional WiFi troubleshooting tool that's always there when you need it.

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