How EMF Is Measured and Why Readings Vary

What an EMF meter actually measures

An EMF meter is really two instruments in one. It measures the electric field, which is produced by voltage, and the magnetic field, which results from the flow of current. The National Cancer Institute separates them clearly: electric fields are measured in volts per meter (V/m), while magnetic fields are measured in microteslas (μT). A display that shows a single "EMF" number is usually reporting one of these fields, or a combined value, so the first step in reading it is knowing which field you are looking at.

The two fields follow different rules. Electric fields appear whenever a device is connected to power, even when it is off. Magnetic fields appear only when current flows. Electric fields are easily shielded by walls and other objects, while magnetic fields pass through buildings, living things, and most materials. That is why a sauna reading can change when a person stands between the meter and the heater, or when a wall sits between the meter and the power cable. For more on how wiring affects these fields, see EMF and electrical fields in wiring.

Units: volts per meter, microteslas, and milligauss

The display on an EMF meter can use different units. The National Cancer Institute specifies volts per meter for electric fields and microteslas, abbreviated μT, for magnetic fields. The National Institute of Environmental Health Sciences, in its own materials, gives an example in milligauss. Some hand-held meters show milligauss rather than microteslas; the conversion is 1 μT equals 10 milligauss. Knowing which unit your meter uses matters because a number written as 2.5 μT looks very different from 25 milligauss.

For radiofrequency fields, which some meters also attempt to read, the National Cancer Institute notes that these are measured in watts per meter squared (W/m²). However, most consumer sauna EMF readings focus on the extremely low frequency fields from the power wiring and heater elements, not on radiofrequency emissions. The relevant fields are the ones described by the NCI, and they are best tracked separately. If you are comparing advertised numbers, also check how terms like low EMF vs ultra low EMF are defined.

Distance and position change the reading

The strength of a magnetic field drops off dramatically as you move away from the source. The NIEHS gives a concrete example: a magnetic field measuring 57.5 milligauss immediately beside a 230 kilovolt transmission line measures just 7.1 milligauss at a distance of 100 feet, and 1.8 milligauss at 200 feet. That same principle applies inside a sauna, just at a smaller scale. A meter held against the heater cabinet will read much higher than one held on the opposite bench, even if the wiring is identical.

Position also matters for the electric field. Because electric fields can be blocked by walls and even by your own body, simply rotating the meter or stepping between the meter and the heater can change the number. For a meaningful comparison, pick a consistent spot, such as the center of the bench, and always hold the meter at the same height and orientation. Measure at that spot with the unit off and then with the heater running or the panels powered, and record both values.

The NCI explains that magnetic fields pass through most materials, but they still weaken with distance. That means the path of the wiring matters. A meter between the heater and the power panel may pick up more than a meter placed perpendicular to the wire run. If you are trying to evaluate a sauna in a showroom, remember that the surrounding building wiring, overhead lights, and other appliances also contribute to the ambient field, so an absolute reading is not a reliable measure of the sauna itself.

Why current and wiring change the numbers

Magnetic fields appear only when current flows. That means a sauna that is off produces no magnetic field from its own circuits, while the electric field may still be present because the unit is energized. When you turn on a traditional heater, the current through the heating elements and supply wires creates a magnetic field around those conductors. A meter near the heater will read higher during the initial warm-up phase, when the elements are fully powered, than when the heater cycles off to hold temperature.

Wiring layout also matters. In a residential sauna, the power cable runs from the electrical panel to the heater. That cable is a current-carrying conductor, and its magnetic field decreases with distance. If the meter is placed near the wall where the cable enters, the reading will be higher than at the center of the room. The NIEHS emphasizes that distance from the source is the main factor, so the physical placement of the meter relative to the cable run is just as important as the placement relative to the heater.

For infrared saunas, which often use multiple low-wattage emitters, the current is spread over many elements, and the magnetic field pattern can be more uniform. Still, the wiring to the control panel and the power inlet will be the strongest source. To get a consistent reading, measure at the same body position you would actually sit in, and measure with the sauna at its normal operating state, not during the initial burst of full current. Understanding this helps when you read public guidance on EMF exposure.

What a single reading does and does not tell you

A single EMF number from a meter is not a health verdict. The National Cancer Institute reviews the scientific evidence and finds that the link between low-frequency EMFs and health effects is not established; most studies show weak or no evidence for adults. The NIEHS similarly notes that the research on childhood leukemia from power-line frequencies showed a weak association, and no evidence for adult cancers. A meter reading is a measure of field strength, not a measure of risk.

That is why many sauna makers avoid publishing absolute EMF numbers. Instead, they may describe their products as low EMF or ultra low EMF. Those terms are not standardized, and the way the reading was taken can make a huge difference. If a manufacturer quotes a number, ask for the measurement conditions: what meter, what units, what distance from the unit, and what state of operation.

The practical use of a meter is comparative: does the field at your head position differ from the field near the heater? Does the reading change when you sit closer to the wall where the power enters? If you are comparing two cabins, measure both in the same way, in the same location, and note the state of the power. That gives you a useful relative sense, even if the absolute numbers are not meaningful on their own. For more on what to ask a seller, see EMF claims: what to ask the seller.

Certification marks are about safety, not EMF

When you see a UL, ETL, or similar mark on a sauna, it indicates that the product has passed electrical safety testing. Intertek, which administers the ETL mark, describes it as proof that a product has been independently tested and certified to applicable safety standards. That means the wiring, heaters, and controls are built to reduce fire and shock risk. It does not mean the product has any particular EMF level, because EMF is not a safety criterion in those standards.

You can use a certification mark as a signal of construction quality, but do not confuse it with an EMF guarantee. The only way to know the field levels at your body is to measure them yourself, or to get the manufacturer's own measurement protocol and replicate it. When you are ready to compare specific models, our sauna heater guide and infrared sauna guide go into the practical differences you should check in person.

What to pick for your use

Questions

What units does an EMF meter use for sauna readings?

Most consumer meters show electric field in volts per meter (V/m) and magnetic field in microteslas (μT) or milligauss. The National Cancer Institute defines these units directly. Radiofrequency fields are measured in watts per meter squared, but sauna EMF discussions usually focus on the lower-frequency fields from wiring and heaters.

Why does the EMF reading change when I stand between the meter and the heater?

Electric fields are easily shielded by objects, including your body. The National Cancer Institute explains that electric fields are weakened by walls and other materials, while magnetic fields pass through most objects. So the meter's reading for the electric field can drop when something blocks the direct path to the source.

Does the sauna being on or off change the reading?

Yes. Magnetic fields are produced only when current flows, so a sauna that is off produces no magnetic field from its own circuit. The electric field from the energized wiring may still be present, because it is caused by voltage. During operation, the magnetic field will be higher while the heater is drawing full current.

Is a single low EMF reading enough to trust?

No. The reading depends on the meter, the unit, the distance, and the operating state. A manufacturer's spec sheet without a clear testing protocol is not meaningful. The National Institute of Environmental Health Sciences emphasizes that field strength drops rapidly with distance, so a number taken with the meter against the heater will differ from one taken at the bench.

What does a UL or ETL mark mean for EMF?

These marks certify electrical safety, not EMF levels. Intertek's ETL mark indicates that a product has been tested to safety standards. That covers fire and shock hazards, but it does not evaluate or guarantee any electromagnetic field output.