a ballpark estimate

a ballpark estimate/figure

a number which is only approximate, but which should be near to the correct number We're expecting sales of the book to generate around $10,000 dollars, although obviously that's just a ballpark figure.
See also: ballpark, estimate
References in periodicals archive ?
This measurement is then multiplied by a reservoir-specific factor--determined by many years' observations--to get a ballpark estimate of evaporation for the entire body of water.
To arrive at a ballpark estimate of how this might translate into urban air pollution, the investigators went back to the 1979 EPA report.