The approximate pressure at the Sun’s core is 250 billion Earth atmospheres.
This enormous pressure is produced by the weight of the Sun’s overlying layers. Gravity compresses the central plasma so intensely that the core reaches temperatures of roughly 15 million kelvin and densities far greater than ordinary matter on Earth. These conditions allow hydrogen nuclei to collide and fuse despite their electrical repulsion.
The Sun’s main energy source is the proton–proton chain, in which hydrogen is gradually converted into helium. The fusion process releases energy that supports the Sun against gravitational collapse and ultimately emerges as sunlight and other radiation. The quoted pressure is a model-based estimate: scientists cannot place a pressure gauge inside the Sun.
The phrase “250 billion atmospheres” means about 250 billion times standard pressure at Earth’s sea level. It describes the central region, not the Sun’s visible surface, where there is no solid boundary and the pressure is vastly lower. The core itself occupies only a small fraction of the Sun’s volume but contains a substantial share of its mass and produces nearly all of its fusion energy.