In this paper, we describe how 3D Euclidean measurements can be made in a pair of uncalibrated images, when only minimal geometric information are available in the image planes. This minimal information consists of a line in a reference plane, and the vanishing point orthogonal to it. Given such limited information, we show that the length ratio of two objects perpendicular to the reference plane can be expressed as a function of the camera intrinsic parameters. Assuming that the camera intrinsic parameters remain invariant between two views, we perform Euclidean metric measurements directly in the perspective images.