Brinkmanship between the United States and North Korea around the subject of nuclear weapons has experts worldwide worried about heightened "tensions." On a practical level, just how expensive are these bombs?

To determine the cost of one nuclear weapon, you have to account for the costs of their production, delivery systems and maintenance.

"South Korean government analysis has put North Korea's nuclear spending at $1.1 billion to $3.2 billion overall," reported Reuters last year, "although experts say it is impossible to make an accurate calculation given the secrecy surrounding the program, and estimates vary widely."

The U.S. government believes North Korean leader Kim Jong Un has up to 60 nuclear weapons, though some independent experts say the total is smaller. If North Korea does indeed have around 60, that puts the cost of each warhead at between around $18 million and $53 million.

The U.S. nuclear program provides a more reliable picture of cost, though not all nuclear development information is public. In "Atomic Audit," published in 1998, Stephen I. Schwartz claimed the U.S. had spent $5 trillion since 1940 on developing and maintaining its nuclear arsenal.

The U.S. government is now estimated to have 6,800 nuclear weapons at its disposal, but America hasn't actually built a new warhead or bomb since the 1990s. "It has refurbished several types in recent years to extend their lifetime," says Dr. Lisbeth Gronlund, a senior scientist and co-director of the UCS Global Security Program.