Heaping table spoon. Squared spoon will be less. And that's only if it is crumbled. Otherwise you can break off piece about twice the siz of the last digit on your index finger and that'll work. No need to get out a ruler it's just that a cubic inch is a common size to weight relation in cooking.
Often times cheese is divided into cubes when you buy it. Or at least it can be bought that way. Otherwise it is a measure of volume that gives you a picture of how much cheese to use.