Earth-sized world
Since surface gravity depends on the star's mass and radius, the method should also help astronomers work out the masses and sizes of distant stars - and any planets orbiting them.
"If you don't know the star, you don't know the planet," said co-researcher Prof Matthews of the University of British Columbia, Canada.
"The size of an exoplanet is measured relative to the size of its parent star.
"If you find a planet around a star that you think is Sun-like but is actually a giant, you may have fooled yourself into thinking you've found a habitable Earth-sized world.