"EMF" gets used as if it were one single thing. It isn't. When we test a product or a home, we're actually measuring three different physical phenomena — electric fields, magnetic fields, and radiofrequency (RF) fields — and each one is created differently, behaves differently, and is measured with a different unit. Understanding the difference is the single most useful piece of background knowledge for reading our database.
First, the big picture: it's all non-ionizing
Everything we measure at EMF Results sits on the low-energy end of the electromagnetic spectrum. That matters, because the spectrum splits into two very different halves. Ionizing radiation — X-rays, gamma rays, and the upper end of ultraviolet — carries enough energy to knock electrons off atoms and damage DNA directly. Non-ionizing radiation — everything from power-line fields up through radio, Wi-Fi, and visible light — does not.
The fields from your wiring, appliances, phone, and router are all non-ionizing. The open scientific questions around EMF are about whether long-term, low-level exposure has subtle effects — not about the kind of direct damage ionizing radiation causes. That's why we publish measurements with context instead of alarm: the honest position is that the fields are real, measurable, and worth understanding, and that health agencies such as the FDA and WHO have found no consistent, credible evidence of harm at everyday exposure levels. Research is ongoing, and our job is to give you the numbers.
Electric fields — pressure from voltage
An electric field exists wherever there is voltage — electrical "pressure" — whether or not any current is actually flowing. A lamp that's plugged in but switched off still produces an electric field, because its cord is energized all the way to the switch. We measure electric fields in volts per meter (V/m).
Three things are worth knowing about electric fields:
- They exist even when nothing is "on." Household wiring in the walls, plugged-in power strips, extension cords, and chargers all create electric fields around the clock.
- They're easy to shield. Walls, trees, furniture, and even your own body block or distort electric fields significantly. This is why readings change so much as you move a meter around a room.
- They fall off quickly with distance. A strong field an inch from an ungrounded cord is often unremarkable a few feet away.
Typical sources in a home: wall wiring behind a headboard, ungrounded lamps and cords, power strips near a desk or bed, and some older electronics.
Magnetic fields — the footprint of current
A magnetic field appears only when current actually flows. Switch a device on and the magnetic field appears; switch it off and the field is gone. We measure magnetic fields in milligauss (mG) — internationally you'll see microtesla (µT), where 1 µT = 10 mG.
Magnetic fields behave very differently from electric fields:
- They pass through almost everything. Walls, wood, brick, and even most metals do little to stop a power-frequency magnetic field. If a breaker panel or a large appliance sits on the other side of a bedroom wall, the field comes through.
- They track how much current is being drawn. A space heater pulling 12 amps produces a much larger field than an LED lamp pulling a fraction of one.
- They drop off fast with distance. Readings right against a running appliance motor can reach hundreds — occasionally more than 1,000 mG — yet fall to background levels within a few feet. Everyday environments mostly range from about 1 mG to low double digits.
Typical sources: appliance motors (refrigerators, fans, hair dryers), breaker panels, transformers and power bricks, building wiring errors, and overhead power lines.
RF fields — wireless communication
Electric and magnetic fields from wiring oscillate at 60 Hz — sixty cycles per second. Radiofrequency fields oscillate millions to billions of times per second, which is what lets them carry information through the air. Your Wi-Fi router works around 2.4 and 5 GHz; your phone uses a range of cellular bands; smart meters typically use 900 MHz and 2.4 GHz.
Because RF is radiated energy traveling through space, we measure it as power density — how much energy passes through a given area — in microwatts per square meter (µW/m²).
- It follows the inverse square law. Double your distance from an RF source and the power density drops to roughly a quarter. This is why distance is the dominant variable in nearly every RF record we publish.
- It's bursty. Many sources transmit in pulses — a router beacons about ten times a second, a smart meter chirps briefly on a schedule, and a phone transmits hard during calls and uploads but far less when idle. That's why we record both peak and average readings.
- Behavior beats wattage. A weak signal can make a phone transmit at maximum power, while a strong signal lets it whisper. Operating mode matters as much as the device itself.
Typical sources: phones, Wi-Fi routers and mesh nodes, Bluetooth devices, smart meters, cordless phones, baby monitors, and nearby cell towers.
Side by side
| Electric field | Magnetic field | RF field | |
|---|---|---|---|
| Created by | Voltage (device can be off) | Current flow (device must be on) | Wireless transmission |
| Unit we use | V/m | mG | µW/m² |
| Blocked by walls? | Largely, yes | Barely at all | Partially (varies by frequency) |
| Typical sources | Wiring, cords, power strips | Motors, panels, power lines | Phones, routers, smart meters |
| Best mitigation | Unplug, distance, grounding | Distance | Distance, duty-cycle awareness |
Why we measure them separately
A single "EMF number" for a product would be meaningless — the three field types don't add up, don't behave alike, and don't come from the same parts of a device. A laptop's power brick is mostly a magnetic-field story; its Wi-Fi card is an RF story; its ungrounded charger cord is an electric-field story. That's why every record in our database logs RF peak and average (µW/m²), magnetic field (mG), and electric field (V/m) as separate values, along with distance and operating mode.
For comparison purposes, our ratings band RF readings as Low below 500 µW/m², Moderate from 500–3,000, and High above 3,000 — and magnetic readings as Low below 4 mG, Moderate from 4–10, and High above 10. These are comparison bands built from commonly referenced exposure guidelines, not medical thresholds; you can read the full reasoning on our How We Test page.