Aperture Area Calculator

Aperture area is the open two-dimensional region through which light, air, radiation, or material can pass. In optics it may describe a lens, telescope objective, stop, or sensor opening. In mechanical and fluid systems it can represent a window, vent, nozzle opening, or cutout. Knowing the clear area helps compare light collection, transmission, loading, and geometric capacity even when openings have different shapes. For a circular aperture, area equals pi multiplied by the square of the radius. Because specifications commonly give diameter, this calculator divides the entered diameter by two before squaring it. A rectangular opening uses width multiplied by height. An elliptical opening uses pi multiplied by its two semi-axes; when full major and minor diameters are entered, that becomes pi times both diameters divided by four. All dimensions must be measured in the same selected unit. The output uses the corresponding square unit. A diameter entered in millimeters produces square millimeters, while dimensions in centimeters produce square centimeters. Converting a length unit changes area by the square of the conversion factor: one square centimeter equals one hundred square millimeters, and one square meter equals ten thousand square centimeters. Select the unit matching the measurements rather than converting only the displayed suffix. Clear area can differ from nominal area. Lens mounts, retaining rings, shutters, central obstructions, rounded corners, mesh, or manufacturing tolerances may block part of an opening. A reflecting telescope with a secondary mirror, for example, has effective geometric collection area equal to the primary area minus the obstruction area. Optical throughput also depends on coatings, absorption, vignetting, and incidence angle, so area alone does not fully predict received energy. Use this calculator for ideal geometric openings with circular, rectangular, or elliptical boundaries. Measure full diameters for ellipses, not semi-axis lengths, and use the unobstructed internal dimensions when clear area matters. The examples demonstrate the formulas with realistic dimensions, but design decisions should preserve suitable precision and include tolerances. For irregular outlines, divide the shape into known regions or use CAD area measurement. For multiple identical holes, calculate one opening and multiply by the count, subtracting any overlap if openings intersect.