POWER
About a tenth of a watt
UKHSA says Wi-Fi signals are very low power, typically 0.1 watt, in both the device and the router, at frequencies broadly the same as FM radio and mobile phones.
See the numbersYour router and devices talk to each other with radio waves.
Some of that energy is absorbed by people nearby, which is why health agencies have measured it. The UK Health Security Agency's view is that Wi-Fi exposure is small compared with international guidelines.
- About 0.1 watt
- Mostly silent
- Well within guidelines
- Measured, not guessed
THE SHORT ANSWER
Low power,
short bursts.
UKHSA sees no reason to stop using Wi-Fi.
It says no extra action is needed to cut exposure.
TIME
Mostly not transmitting
In lessons at 6 schools, the 146 laptops studied were sending radio signals only 0.08% of the time on average. Access points averaged 4.79%.
Check each device
DISTANCE
Further from the body
UKHSA says Wi-Fi exposure is likely to be lower than from a mobile phone held for a voice call, because Wi-Fi antennas tend to be further from the body.
What it meansGeneral information only, not medical advice. For advice about your own health, speak to a doctor, pharmacist or other qualified health professional.
FOUR THINGS TO KNOW
Use it
with confidence.
UKHSA says no additional action is necessary, communally or individually, to reduce Wi-Fi exposure further. These points explain why.
It is the same kind of signal
Wi-Fi uses bands near 2.4, 5 and 6 GHz, broadly the same frequencies as FM radio and mobile phones.
Heating is the known effect
WHO and ICNIRP both say heating is the main effect of radio waves. Everyday levels are very much lower than those needed for significant heating.
Distance does the work
Wi-Fi antennas usually sit further from the body than a phone held to your ear, which is one reason exposure tends to be lower.
Look at other causes too
WHO says evidence does not support a link between low-level fields and symptoms such as headaches or fatigue, and some may come from noise or other factors.
TWO NUMBERS WORTH KNOWING
How strong it is,
and how often.
One figure from UKHSA's guidance,
one from its measurements in schools.
0.1 watt
Typical output power of a router or device
That is 100 milliwatts, in both the user device and the router. UKHSA's measurement programme found Wi-Fi exposures small in relation to the ICNIRP guidelines.
WI-FI AND HEALTH · UKHSA
0.08%
Average share of time spent transmitting
Applying measured duty factors, the maximum time-averaged power density from a laptop was 220 microwatts per square metre at 0.5 metres.
146 LAPTOPS · KHALID ET AL. 2011
ICNIRP says the only substantiated health effect of radio-frequency fields is heating of tissue, and its limits are set below the threshold where that becomes harmful, with extra conservative margins.
A QUICK DEVICE CHECK
How often is it
actually sending?
Wi-Fi sends data in short bursts, and guidelines allow exposure to be averaged over time. Pick a device to see the share of time it was transmitting during real school lessons.
Measured with radio packet capture in 6 UK primary and secondary schools. Homes will differ with how the network is used.
WHY THE SURFACE MATTERS
Higher frequencies
stay nearer the skin.
Radio waves can pass into the body, and the higher the frequency, the less deeply they go. UKHSA notes that at higher frequencies the absorbed energy, and any heating, becomes more confined to the body surface.
ICNIRP limits cover all frequencies up to 300 GHz, well beyond Wi-Fi's 6 GHz. They are set in relation to the levels known to cause harm, with conservative margins added for scientific uncertainty, and measured public exposures remain well within them.
In conversation
Questions people ask
Is Wi-Fi harmful to health?
UKHSA says there is no consistent evidence that exposure to radio signals from Wi-Fi devices adversely affects the health of the general population, and sees no reason why Wi-Fi should not continue to be used.
How powerful is a Wi-Fi router?
UKHSA gives a typical figure of 0.1 watt (100 milliwatts) for both the router and the user device.
Is Wi-Fi in schools safe?
The Health Protection Agency, now UKHSA, measured networks in schools and found exposures small in relation to ICNIRP guidelines. UKHSA sees no reason not to use Wi-Fi in education.
Is Wi-Fi exposure more than a mobile phone?
UKHSA's study found Wi-Fi devices generally have lower time-averaged output power than mobile phones, and exposure is likely to be lower than a phone used for a voice call.
What about electromagnetic hypersensitivity?
WHO says there is little scientific evidence to support it: people did not show consistent reactions under properly controlled conditions, and there is no accepted biological mechanism.
Sources
Each figure on this page comes from the sources below.