Yes. For a fisheye, the simplest practical method is to measure the angle directly rather than relying on image scale.

Mount the camera on a tripod in an open area. Mark the point on the ground directly below the camera. Then find the leftmost and rightmost positions in the scene that are just barely still visible in the frame. A simple way is to have a person walk to each side until they are at the edge of the image, and mark those spots on the ground.

Now draw or stretch lines from the tripod’s ground point to the left and right marks. Measure the angle between those two lines with a protractor or by basic triangle geometry. That angle is the horizontal field of view.

This works well for fisheye lenses because it measures the actual angular coverage of the system, not the changing magnification across the image. A tape measure on a wall can also work in principle if you know the distance and visible width, but the direct angle-measurement method is more robust and avoids issues caused by fisheye distortion.