The ongoing irony in "How Much Land Does a Man Need" has to do with the fact that Pakom cannot stop trying to enlarge the amount of land he is going to acquire for his one thousand roubles. He keeps walking farther and farther, trying to enclose more and more of the rich land. He inevitably ends up getting into time trouble because the sun is setting and he is a long distance from the point he has to reach in order to make a complete circuit of the land he wishes to acquire. He has already tired himself out with his long day's walking, and then he is forced to walk faster and faster and finally to start running in order to reach his goal. The final irony is contained in the very last words of Tolstoy's story:
His servant picked up the spade and dug a grave long enough for Pahom to lie in, and buried him in it. Six feet from his head to his heels was all he needed.
That answers the question asked in the title, "How Much Land Does a Man Need?"