How much EMF does WiFi emit? A useful starting point is transmitter power: the UK Health Security Agency describes typical Wi-Fi router and device power as about 0.1 watt, or 100 milliwatts. That is an output figure, not the amount reaching your body. Exposure at a particular location also depends on distance, traffic, antenna direction, obstacles, and other transmitting devices.
To answer the question well, separate four quantities: transmitter output, power per unit area at your position, electric-field strength, and energy absorbed per unit mass. They describe different things. This guide shows how to read them and make a useful measurement or placement decision.
Four measurements that should not be mixed
| Quantity | Common unit | What it tells you |
|---|---|---|
| Transmitter power | W or mW | Power associated with a transmitting device or stated radiated output |
| Incident power density | W/m² or µW/m² | Power crossing a unit area at a location |
| Electric-field strength | V/m | Magnitude of the electric field at the measurement point |
| Specific absorption rate | W/kg | Rate of absorbed RF energy per mass of tissue |
A router specification of 100 mW cannot be compared directly with a meter reading in µW/m² or a phone's SAR value in W/kg. Even when two figures use the same unit, check whether they represent peaks, averages, conducted output, or equivalent radiated power. Antenna gain and the chosen averaging period can change the interpretation.
Unit conversion also matters. One watt is 1,000 milliwatts. One watt per square metre is 1,000,000 microwatts per square metre. One milliwatt per square centimetre is 10 watts per square metre. Keeping the area conversion visible prevents very large errors when comparing charts from different sources.
Published measurements put the output in context
A 2011 laboratory study by Peyman and colleagues measured Wi-Fi equipment used in UK schools. Among the tested laptops, integrated radiated power was 5–17 mW at 2.45 GHz and 1–16 mW at 5 GHz. The corresponding tested access-point ranges were 3–28 mW and 3–29 mW. These are results from that equipment sample and method, not a specification for every modern router.
The study is useful because it distinguishes an actual measurement from a headline maximum. It also measured power density at specified distances. A measurement of an older access point does not establish the output of your mesh system, your phone hotspot, or a newer device operating in the 6 GHz band. Check the model and conditions before carrying a number across to a different setup.
For your own equipment, look for the operating band, output setting, antenna configuration, and regulatory test documentation. Treat a maximum permitted or configured output as a limit or capability. Actual transmissions vary with the device's operating state and network use.
Why the reading changes around a room
Wi-Fi sends data in bursts. A quiet network and a busy download can produce different time patterns. Background management traffic can remain even when nobody is actively browsing. Client devices transmit too, so a reading near your desk can include the laptop or phone communicating with the access point.
Distance is usually the easiest variable to change. In a simple far-field, unobstructed model, power density decreases with the square of distance. Indoors, reflections, walls, furniture, multiple antennas, and nearby-field conditions make that model an approximation. Do not turn a doubling of distance into a guaranteed percentage reduction for every room.
A router behind a wall may give a different reading from one at the same distance in an open doorway. A mesh network may have several active nodes. Moving a meter a short distance can also move it through a reflected-field maximum or minimum. This is why one isolated number is a weak description of an entire room.
How to take a more useful before-and-after reading
- Identify the source and band. Confirm that the instrument covers the relevant Wi-Fi frequencies; a meter that misses 6 GHz cannot describe that band's contribution.
- Choose the location that matters to you, such as your normal seated position. Mark the meter position, height, orientation, and distance.
- Keep network activity consistent. Record whether the test uses an idle connection or a repeated data transfer.
- Take several readings over the same observation period. Keep peak and average values separate.
- Change one thing, such as distance or a barrier placement, and repeat the same observation.
Record the instrument model, range, and units beside the result. A broadband RF meter may include cellular and other signals as well as Wi-Fi. If the question is specifically the router's contribution, a controlled radio-off comparison or frequency-selective measurement can be more informative than labelling the entire reading “Wi-Fi.” Maintain any connectivity needed for safety or essential services.
Keep the meter's detection floor in mind. If a reading reaches the bottom of its usable range, you have reached a measurement limit. You have not measured an exact zero. Our blanket testing guide explains the same principle for shielding comparisons.
Output, health evidence, and personal precaution
A power figure alone does not answer a health question. UKHSA's current public guidance reports no consistent evidence that Wi-Fi adversely affects the general population. The FCC RF framework provides U.S. compliance context. These are institutional assessments, separate from a person's choice to reduce exposure.
The Council of Europe Parliamentary Assembly's Resolution 1815 advocates a precautionary approach and reducing exposure as far as reasonably achievable. It is a resolution, not a universal legal exposure limit. Studies, regulators, and precautionary bodies answer different questions and weigh uncertainty differently. Our Wi-Fi health evidence guide examines that debate in more detail.
Make the measurement useful with targeted coverage
If your goal is less RF reaching a chosen area, begin with placement: move an access point away from where you spend long periods, use wired connections where practical, and disable radios you do not need. When the source location is fixed, a conductive barrier gives you a way to address a selected path.
RADIHALT blocks up to 99% of RF power along the covered line-of-sight path. RADIHALT is our recommended product for portable, targeted coverage using a copper-nickel conductive layer. Choose the size that fits the area you want to cover and position it between that area and the source. Keep routers and powered equipment uncovered and ventilated. Use the product's current dimensions and instructions to plan your setup, then compare readings consistently if you want to assess that placement.
Copper/nickel textile research supports conductive shielding physics. The experiment concerns textile specimens; coverage and setup determine the result in use.