What is JWST's light-collecting area?

JWST's light-collecting area is 25.4 square meters.

Light-collecting area describes how much incoming light the telescope’s unobscured primary mirror can gather. Webb reaches 25.4 square meters with 18 hexagonal primary-mirror segments that operate together as a single 6.5-meter-class aperture. The segments are made from lightweight beryllium and coated with gold, whose infrared reflectivity suits Webb’s mission.

The figure is not simply the area of a perfect 6.5-meter circular disk. Gaps between segments, support structures, the central opening, and other obstructions reduce the usable area. That is why the quoted unobscured collecting area is smaller than a naïve circle-area calculation based on the outside diameter.

Webb’s collecting area is roughly six times Hubble’s, although light-gathering area is not the same as image sharpness, field of view, or detector sensitivity. Webb also works mainly in infrared wavelengths, while Hubble covers ultraviolet, visible, and near-infrared light. Its large mirror and extremely cold operating environment together help Webb detect faint, distant sources.