Pinhole Image Size Calculator

About this calculator

A pinhole camera has no lens — light rays from an object pass in straight lines through a tiny aperture and land on the film or sensor plane inverted, a principle known since antiquity as the camera obscura effect. The size of that projected image is governed by simple similar-triangles geometry: image size = object size × (image distance ÷ object distance), where image distance is how far the film plane sits behind the pinhole and object distance is how far the subject is in front of it.

This calculator takes the real-world object size and both distances and returns the projected image dimensions, letting you predict framing before you shoot. Pinhole photographers building or calibrating a camera, physics teachers demonstrating optics, and darkroom hobbyists use it to figure out how large a subject will appear on the film for a given pinhole-to-film distance, since there's no viewfinder to check the frame directly.