How much mass does the Sun convert into energy each second via fusion?

The Sun converts about 4.26 million tonnes of mass into energy each second via fusion. In its core, roughly 600 billion kilograms of hydrogen are fused into helium every second. The helium nucleus has slightly less mass than the four hydrogen nuclei that formed it; about 0.7% of the original mass becomes energy according to E = mc².

That mass deficit powers the Sun's luminosity of approximately 3.846 × 10²⁶ watts. The energy eventually travels outward through the radiative and convective zones before escaping from the photosphere as sunlight and other radiation. Neutrinos also carry some energy directly away from the core.

A common mix-up is confusing the mass converted into energy with the total amount of hydrogen consumed. The Sun processes about 600 million tonnes of hydrogen per second, but only around 4.26 million tonnes becomes energy; most ends up in helium. This enormous rate is still tiny compared with the Sun's mass, roughly 1.989 × 10³⁰ kilograms.