milligals

Milligal, abbreviated mGal, is a unit of acceleration used in gravimetry and geophysics. It is defined as one thousandth of a gal, where a gal is the unit of acceleration equal to one centimeter per second squared.

Since 1 gal equals 0.01 meters per second squared, 1 milligal equals 0.001 gal, or 1 × 10^-5 meters per second squared. In practical terms, standard Earth gravity is about 9.80665 m/s^2, which is roughly 980,665 milligals. The milligal is part of the non-SI gravitational units frequently used in the field.

Milligals are used to express small variations in the Earth's gravitational field detected by gravimeters. These measurements underpin gravity surveys in geology, mineral exploration, geodesy, hydrology, and tectonics. Data are often reported in milligals because the observable anomalies caused by subsurface density contrasts typically fall within this scale. Gravimeters must resolve changes on the order of a few milligals or less, depending on the application.

Notation commonly uses the symbol mGal. Although not part of the International System of Units, the milligal remains a standard unit in geophysics and related disciplines due to its convenience for recording gravity variations. For conversions to SI units, multiply by 1 × 10^-5 to obtain meters per second squared.