What “Q” actually means in fusion
Q is fusion energy out divided by energy in. Q=1 is scientific breakeven; a power plant needs Q well into the tens. We explain why NIF's “gain 4” and a plant's Q aren't the same number.
Fusion researchers report progress with a single ratio: Q, the fusion energy released divided by the energy put in. When Q is below 1, an experiment consumes more than it makes. Q=1 is scientific breakeven — the point where the reactions return as much energy as was delivered to the fuel.
That sounds like the finish line, but it is only the first one. A commercial power plant still has to run its lasers, magnets, cooling and controls and sell electricity at the end. For that, the plant-level gain has to be far higher — engineers usually talk about Q in the tens once every overhead is counted.
This is why NIF's headline “target gain” of about 4 and a power plant's Q are not the same number. NIF's figure compares fusion output to the laser energy that reached the fuel pellet, not to the much larger energy the whole facility drew from the wall. Both are real; they answer different questions. On this tracker we record the reported figure with its source so you can see exactly which Q is being claimed.