Nanotesla — geomagnetic anomaly units
1 nT = 10⁻⁵ Gauss = 10⁻⁹ T. Small numbers — but big enough to map buried pipelines, unexploded ordnance and archaeological features.
Geomagnetism lives four decades below MRI physics. The tools are the same (measure B), but the units — nanotesla — reflect signals millions of times smaller than a fridge magnet.
The exact factors
1 T = 10⁹ nT > Earth's total field: 25 000–65 000 nT depending on latitude > Diurnal variation: 20–80 nT > Solar storm: hundreds of nT for hours
Where each is used
Nanotesla: geological surveys, archaeological prospection, UXO clearance, borehole logging. Gamma (γ): a legacy CGS unit, 1 γ = 1 nT exactly. Milligauss: sometimes used in older US survey literature (1 mG = 100 nT).
Worked example — buried oil drum
A 200 L steel drum buried 2 m deep creates a magnetic anomaly of ~10–30 nT at the surface. Instrument noise floor is ~0.1 nT, diurnal drift ~5 nT/hr — surveys correct for base-station reference readings to keep signal above noise.
Recap
nT for geomagnetism. Correct for diurnal drift. Same physics as MRI, six orders of magnitude smaller.
Try the converters mentioned in this article
FAQ
Is 'gamma' still used?+
In older survey reports, yes. 1 γ = 1 nT — the switch was purely nomenclature.
How sensitive are modern magnetometers?+
Fluxgate ~0.1 nT, proton precession ~0.01 nT, SQUIDs down to femtotesla in shielded rooms.
This article was written by The Turbo Unit Converter engineering desk (Applied metrology & engineering units) and last reviewed on 2026-07-07 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.