How to Measure Magnification

Determine the width of the microscope's field of view by placing a slide with a graduated scale on the stage. The field of view is the area viewed under the microscope. While observing through the microscope, align the graduated scale across the field of view to measure its width.

Remove the slide with the graduated scale and place a slide with the desired specimen on the stage of the microscope. Estimate the percentage the specimen stretches across the field of view.

Multiply the percentage of the field of view occupied by the specimen by the measured width of the field of view. The result is the actual size of the specimen. For example, a specimen that stretches about half (50 percent) of a field of view that measures 1 mm across can be estimated to have a length of about 0.5 mm (1 mm x 50 percent = 0.5 mm).

Measure the size of the object in the drawing or photograph using a ruler. For objects that are not spherical, it is important to measure using the same scale such as millimeters and along the same axis of the image on the photograph and in the microscope.

Calculate the magnification by dividing the size of the recorded image by the actual size of the object. Continuing the example, if a drawing of the object measures 20 mm long and the actual length of the object is 0.5 mm, then the magnification in the drawing is 40x (20 mm / 0.5mm = 40x). This means the image is 40 times larger than the size of the object.