Magnetic force lost when you break a magnet?

if you have a magnet that pulls 40lbs of force if you broke that into 2 how much force will each magnet pull.

i have some neodymium magnets from hardrives and i wanna break them up but i wanna know if thats gunna make them lose alot of force. anyone know the formula for calculating such a thing? or better yet just plane old english will work lol. thanks