Magnetic Flux Density Converter (T / mT / µT / Gauss)
Magnetic flux density (symbol B) measures the strength of a magnetic field. Its SI unit is the tesla (T); the older CGS unit is the gauss (G). Enter a value in either side and the tool converts it instantly, and also fills in the full T / mT / µT / G / mG grid — making it easy to compare MRI main fields (1.5–7 T), fridge magnets (~5 mT), Earth's surface field (~50 µT) and EMF-meter readings (mG / µT) that span many orders of magnitude.
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Live value in every magnetic-flux-density unit
Tip: 1 T = 10 000 G is an exact definition (NIST SP 811). Earth's surface field is ~50 µT ≈ 0.5 G; a fridge magnet is ~5 mT ≈ 50 G; a 3 T MRI scanner is about 60 000 × stronger than Earth's field.
- µT Earth's magnetic field (25–65 µT), household appliance leakage, low-level environmental readings
- mT Fridge-magnet stickers, loudspeaker gaps, Hall-effect sensors, motor stators
- T Hospital MRI main field (1.5 T / 3 T / 7 T), strong neodymium magnets
- G CGS-Gaussian unit — still common in older physics, astronomy and lab notes
- mG EMF meter readings, ELF environmental exposure surveys, fine geomagnetic variations
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Formula
1 T = 10⁴ G (exact, NIST SP 811) 1 mT = 10⁻³ T = 10 G 1 µT = 10⁻⁶ T = 0.01 G = 10 mG 1 G = 10⁻⁴ T = 100 µT 1 mG = 10⁻³ G = 10⁻⁷ T = 0.1 µT
- · Unit definition: the tesla (T) is the SI coherent derived unit, 1 T = 1 Wb/m² = 1 kg·s⁻²·A⁻¹ (BIPM SI Brochure §2.3.3).
- · CGS-to-SI: 1 T = 10 000 G exactly, defined by the historical correspondence between electromagnetic-CGS and SI units (NIST SP 811, ISO 80000-6).
- · This tool only converts B (flux density). In CGS, the magnetic field strength H uses a different unit (oersted, Oe) with different dimensions, and is intentionally out of scope.
- · Earth's surface total field varies roughly 25–65 µT (0.25–0.65 G) depending on latitude (NOAA / IGRF); ~50 µT is a textbook mid-latitude figure.
- · WHO's ICNIRP reference level for the general public at 50 / 60 Hz is 200 µT (= 2 G); the 5 G line (≈ 0.5 mT) commonly drawn around an MRI scanner marks where ferromagnetic objects become unsafe.
- · µT and mG are typical small units on consumer EMF meters: 1 mG = 0.1 µT, so a reading of "20 mG" equals 2 µT.
Frequently asked
What is the exact ratio between gauss (G) and tesla (T)?
Exactly 10 000 gauss = 1 tesla. This is a defined (not approximate) conversion listed in NIST SP 811 and ISO 80000-6, coming from how the old electromagnetic-CGS system was mapped onto SI. Therefore 1 mT = 10 G, 1 µT = 0.01 G = 10 mG. Older physics texts and astronomy / geomagnetism papers still use gauss; modern medical imaging, engineering and most physics research use T / mT / µT as the default.
How strong is a "3 T" MRI scanner in everyday terms?
Clinical MRI scanners typically come at 1.5 T, 3 T or 7 T. A 3 T field equals 30 000 G — roughly 60 000 × stronger than Earth's ~50 µT (0.5 G) surface field. That is why MRI suites mark the "5-gauss line" (≈ 0.5 mT) on the floor: any ferromagnetic object (keys, trolleys, oxygen cylinders) that crosses it can be violently pulled into the bore, which is a well-documented accident pattern.
My EMF meter reads "20 mG" — is that high or unsafe?
20 mG = 2 µT. The WHO / ICNIRP 2010 reference level for general-public exposure at 50 / 60 Hz is 200 µT (= 2 000 mG), so 20 mG is about 100 × below that limit — elevated for ambient indoor readings but still within the common range you would see near appliances or a main breaker panel. To reduce it further, move away from the source or reduce exposure time. Note that EMF meters usually report an RMS value, not the instantaneous peak.
Why is oersted (Oe) not in the list?
Because the oersted (Oe) is a unit of magnetic field strength H, not magnetic flux density B — they are different physical quantities with different dimensions (B is in T, H is in A/m in SI). In vacuum 1 Oe ≈ 79.5775 A/m, but mixing B-units and H-units freely is a common source of errors, so this tool deliberately restricts itself to the five common units of B (T, mT, µT, G, mG).
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