Magnification Calculator
Find magnification from image and object distances.
Magnification compares image size to object size.
How the Math Works
The Magnification Calculator uses the fundamental optical formula m = -di/do, where m represents magnification, di is the image distance, and do is the object distance. The negative sign indicates that the magnified image is inverted relative to the original object. To calculate magnification, simply divide the image distance by the object distance and apply the negative sign. For example, if an object is placed 10 cm from a lens and the image forms 30 cm away, the magnification would be -30/10 = -3, indicating the image is three times larger and inverted.
Practical Applications
To use this calculator practically, first measure or determine the object distance (the distance from the object to the lens or magnifying device) and the image distance (the distance from where the image forms to the lens). Enter these values into the calculator, ensuring both measurements are in the same units (centimeters, meters, etc.). The calculator will automatically compute the magnification. This is particularly useful for photographers determining how much a telephoto lens will enlarge their subjects, or for students working on optics problems involving lens systems.
Day-to-Day Use
Understanding magnification helps in everyday activities like selecting the right magnifying glass for reading small print or examining objects, setting up microscopes for optimal viewing, or choosing camera lenses for photography. It explains why smartphone cameras can't zoom in indefinitely and helps you understand the limitations of your reading glasses or the magnification power of different tools. Whether you're assembling tiny parts, reading fine text, or simply curious about how lenses work, this calculator demystifies the relationship between object placement and image size.
Worked example
image 15, object 30 → −0.5 (half size, inverted).
FAQ
Negative?
The image is upside-down (real image).