Evergreen explainer · neutral data, no opinion

Fusion energy gain (Q)

Current verified value

4.1

NIF / LLNL · inertial confinement · target gain 4.13

What it measures

Energy out divided by energy in. Q=1 is scientific breakeven; a power plant needs Q well above 1. The single number for how close fusion is.

NIF / LLNLlaser / inertial, gain 4.13 (2025)Q 4.1

JET (UKAEA)tokamak, 16 MW (1997)Q 0.7

now4.1

goalQ ≈ 10

baselinescientific breakeven Q=1

engineering gain a commercial power plant needs