Tough to say without scales. Though not a sand bass I’ve had 14.75” crappie weigh 2.25 lbs and a 17” crappie weigh 2.2 lbs. The 17” looked like it was on crack. Have seen a lot between these two sizes with all weighing different up to 2.75 lbs. 18” fat as you say I’d guess 3 - 4 lbs. Always have scales.