“Tactical nuclear weapons are often called “battlefield” or “theater” weapons to distinguish them from much more powerful strategic nuclear weapons, but they are far more destructive than conventional weapons. During the Cold War, tactical nuclear weapons had yields ranging from tens or hundreds of tons of TNT to thousands of tons. These weapons came in many forms: gravity bombs, short-range missile warheads, anti-aircraft missiles, air-to-air and air-to ground missiles, anti-ship and anti-submarine torpedoes and even demolition devices or mines. Reportedly, the smallest tactical weapon in the Russian nuclear arsenal has a yield of about one-third the size of Hiroshima or Nagasaki bombs, or equivalent to about 5,000 tons of TNT.
There are a few ways that such a tactical nuclear weapon could be used to fire the kind of “warning shot” envisioned in Russian military doctrine. These options come with increasing degrees of risk for the U.S., Ukraine and its allies, and for Russia.”
https://www.politico.com/news/magazine/2022/05/16/scenarios-putin-nukes-00032505